Proceeding of the Second National Conference of the Ethiopian Fisheries and Aquatic Sciences Association (EFASA) February 20-21, 2010, Bahir Dar, Ethiopia
“Management of shallow water bodies for improved productivity and peoples' livelihoods in Ethiopia”
Bahir Dar, 2010
Management of shallow water bodies for improved productivity and peoples' livelihoods in Ethiopia
19- 22 February 2010 Second National Conference of the Ethiopian Fisheries and Aquatic Sciences Association (EFASA) Bahir Dar Ethiopia
Published by EFASA Addis Ababa Ethiopia Website: https://www.aau.edu.et/index.php/efasa-home Email: [email protected]
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Title : Management of shallow water bodies for improved productivity and peoples' livelihoods in Ethiopia Publisher : The Ethiopian Fisheries and Aquatic Sciences Association (EFASA), Addis Ababa, Ethiopia
Copyright : EFASA, 2010 All right of the publisher are reserved by law. This publication is however free for all non-commercial education purposes. Any other uses require official consent and approval of EFASA.
ISBN : 978-99944-819-1-0
The articles in this proceeding can be referred to as for instance:
Ayalew wondies (2010): Current land use practices and possible management strategies in shore area wetland ecosystem of Lake Tana: Towards improving livelihoods, productivity and biodiversity conservation. In: Management of shallow water bodies for improved productivity and peoples' livelihoods in Ethiopia . Editors: Seyoum Mengistu and Brook Lemma, EFASA, Addis Ababa University Printing Press, Addis Ababa, 9-16.
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Table of contents
Preface
Acknowledgments
Opening remarks : Dr. Brook Lemma, President of EFASA 1
Keynote address : His Excellency Ato Alemu Admas, Deputy Bureau Head, Bureau of Agriculture and Rural Development, Bahir Dar, Amhara region, Ethiopia 4
Opening speech : Ato Tesfaye Mengist, Process Owner for Extension, Bureau of Agriculture and Rural Development, Bahir Dar, Amhara Region, Ethiopia 7
Part ONE: Oral presentations
Current land use practices and possible management strategies in shore area wetland ecosystem of Lake Tana by Ayalew wondie 9
Enhancing wetland ecosystem services through engineering interventions: a management plan for treatment of municipal waste water, Bahir Dar Gulf of Lake Tana, Ethiopia by Gorraw Goshu 17
Assessment of current fish status of Koga River and Dam, Mecha Woreda, West Gojjam, Ethiopia by Mihret Endalew Tegegnie 24
National Aquaculture development strategies of Ethiopia: a road map to building a healthy and dynamic aquaculture sub-sector by Hussien Abegaz Issa 31
The aquaculture boom in the west shoa zone, oromia, Ethiopia by Daba Tugie 40
The effect of stocking density and supplementary feed on growth performance of Nile Tilapia (( Oreochromis niloticus Linneaus, 1758) in cage culture system in Lake Elen, Ethiopia by Abebe Tadesse, Abebe Getahun and Seyoum Mengistu 48
Pond fish farming in practice: challenges and opportunities in Amhara region b y Chalachew Aragaw 61
Fish post-harvest losses and the possible ways to reduce the losses in Lake Koka by Yared Tigabu 69
Comparative of growth performance in pond culture of four Nile tilapia (Oreochromic niloticus) strains collected from different Ethiopian freshwater lakes by Kassaye Balkew Workagegn and Gjoen Hans 74
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Technical and socio-economic characteristics of fishing activities fish handling and processing in Ethiopia by Abera Degebassa 104
Economic analysis of capture fishery: The case of Lake Babogaya by Lemma Abera Hirpo 108
Part TWO: Poster presentations
A comparative study on the effect of three drying methods for better preservation by Abera Degebassa and Tesfaye Alemu Aredo 117
The effect of supplementary feeding on water quality during cage culture practice of Oreochromis niloticus in Lake Kuriftu, Ethiopia by Ashagrie Gibtan, Abebe Getahun and Seyoum Mengistu 123
Growth of Labeobarbus spp. in aquaria and pond conditions by Belay Abdissa, F. N. Shkil, K. F. Dzerzhiskii, Wondie Zelalem and Mesfin Tsegaw 133
Growth, mortality and recruitment of Clarias gariepinus in the northern part of Lake Tana by Belay Abdissa 139
Species composition and relative abundance of fish species in major rivers of Amhara region,Abay and Tekeze basins, Ethiopia by Dereje Tewabe and Goraw Goshu 146
The biodiversity of fish communities of nine Ethiopian lakes along a north-south gradient: threats and possible solutions by Eshete Dejen, J. Vijverberg and Abebe Getahun 155
Benthic macroinvertebrate metrics in relation to physic chemical parameters in some selected rivers in Ethiopia by Getachew Beneberu and Seyoum Mengistu 161
Assessment of downstream dispersal of juveniles of the migratory riverine spawning Labeobarbus spp. of Lake Tana b y Wassie Anteneh, Abebe Getahun and Eshete Dejen 172
Ecological assessment of Dibankobahir wetland ecosystem in North West Amhara Region, Ethiopia by Yezbie Kassa 181
Survey of anthropogenic impact on rift valley water bodies: The case of Lake Zeway, Langanoo and Abijata Mathewos by Mathewos Hailu , Getachew Senbete, Megersa Hindabu and Birhanu Taddese 210
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Preface
The Ethiopian Fisheries and Aquatic Sciences Association (EFASA) has been around for the last three years only. Since then it has conducted conferences and sponsored international ones such as the Pan-African Fish and Fisheries Association (PAFFA) at the Economic Commission for Africa Hall in 2008 and the aquaculture conference organized by the British Council and the Development Partnership in Higher Education (DelPHE) at Bahir Dar in 2009. It has published the proceedings of its national conferences. The first one is available at its website and the second is this one you are now reading. To achieve these goals bringing together all the members under one umbrella of EFASA was not an easy task and as well carrying out the day-to-day activities of the association. Thanks to all EFASA members who have always showed the motivation and interest to remain at standby to cooperate and EFASA always remains indebted to all those institutions and individuals who assisted it financially and technically in all its endeavors.
This proceeding presents works of many young Ethiopians who had to conduct their research with the obvious hardships we see in developing countries. If there are any shortcomings in their research reports, please realize that it is not lack of capacity in the persons as such but the hardships to conduct research, lack of field and laboratory facilities and the subsistence way of life they carry on with. They proceed this way and EFASA continues to bring their efforts to daylight until such time as our country pulls through development to reach where other countries have done so.
On behalf of the Executive Committee of EFASA and myself I seize this opportunity to congratulate all the authors for their achievements and the supporters that provided them with the financial and technical resources. As President of EFASA I strongly believe with the utmost confidence that EFASA members will continue to produce usable knowledge and technologies in the field that will contribute their shares towards the benefits of the general public and the development of this nation.
Brook Lemma, PhD President of EFASA
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Acknowledgments
The Ethiopian Fisheries and aquatic Sciences association (EFASA) would like to extend its heartfelt gratitude to the following institutions that have supported it to finance the second Annual Conference on "Management of shallow water bodies for improved productivity and peoples' livelihood in Ethiopia" to be held from 20-21 February 2010 in Bahir Dar.
1. Bureau of Agriculture and Rural Development, Rural Capacity Building Project, Amhara Regional State, Bahir Dar 2. Amhara Regional Agricultural Research Institute, ARARI 3. Food and Agriculture Organization Sub-Regional office for Eastern Africa, Addis Ababa 4. Development partnership in Higher Education (DelPHE), UK 5. Ambo University 6. Haramaya University 7. Addis Ababa University 8. The Ethiopian Quality Standards Authority, Addis Ababa 9. The Ethiopian Agricultural research Institute (EAIR) 10. Department for international Development (DFID) 11. The British council 12. and others
EFASA extends its acknowledgements to the Regional Organizing Committee composed of Ato Alayu Yalew and Ato Belay Abdissa from Bahir Dar Fisheries and Aquatic Life research Center, Dr. Ayalew Wondie, Bahir Dar University, and Ato Chalachew Argaw from Bureau of Agriculture and Rural Development.
EFASA, 2010
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Ma nagement of shallow water bodies ..., EFASA 2010
Opening remarks by the President of EFASA
• His Excellency, Ato Alemu Admas, Deputy Bureau Head, Bureau of Agriculture and Rural Development • Dear Ato Tesfaye Mengist, Process Owner for Extension, Bureau of Agriculture and Rural Development • Dear invited guests • Ladies and gentlemen
It is a great pleasure and honor for me to welcome you all to this Second Annual Conference of the Ethiopian Fisheries and Aquatic Sciences Association (EFASA) organized under the theme of "Management of shallow water bodies for improved productivity and peoples' livelihoods in Ethiopia" to be held here in BahirDar from today February, 19-22, 2010.
In its efforts to meet its objectives with success, EFASA organizes the annual conference to bring together scientists, development agents, government institutions, non-governmental organizations and the general public who make their livelihoods in this sector of the country’s economy with the attempt to exchange new ideas, technologies and to bring into the spotlight this area of development that has been left aside for a long time now. As was witnessed in Zwai last year at the first national conference, this year EFASA made its purposeful choice to come to BahirDar because any impact made at BahirDar will make a difference in food security and improved livelihoods of the people. Obviously, aquatic resources that are rich in their food values for children, the sick and the aged and that has remained untapped for so long will surely make a difference if we continue giving it the attention it deserves.
Since the Zwai first national conference, the Ethiopian Government issued Charities and Societies Proclamation No. 621/2009 which EFASA took as a great opportunity to make itself known as one of the national professional associations to be recognized as one that stands for the service of national and international interests. It then worked relentlessly to re-organize its thinking and work strategy and produced all the necessary documents and justifications and obtained its legal status among renowned sister associations of the nation.
As this national and international service of EFASA was proven in the past when it took the leadership to organize the Pan-African Fish and Fisheries Association (PAFFA) at the Economic Commission for Africa, Addis Ababa in 2008, it is now doing the same this year with the organization of a half-day workshop tomorrow, 21 February 2010, on behalf of Development of Partnership in Higher Education (DelPHE), Department for International Development (DFID) and the British Council, all from UK. This is again a landmark for EFASA to take such great leaps in so short a time of its formation. It the coming year 2011, EFASA envisages hosting another international conference under the theme of “Spirulina for Africa” which is initiated and organized by the prominent Ethiopian scientist Dr. Amha Belay. At present EFASA is informed that this conference has acquired some international funding and is finalizing the list of participants. EFASA, as host of such an international conference is looking forward to it with great expectations and as a major window of opportunity again to radiate itself into the international arena. Incidentally I must mention that Dr. Amha Belay is the first person who initiated aquatic science research at Addis Ababa University and in whose footsteps we all thrive today.
EFASA has represented its members at various conferences organized in different parts of the country. Among the many the most prominent was the one conducted at Ambo University when it launched the first aquaculture masters program in Ethiopia. At this conference EFASA members and
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Ma nagement of shallow water bodies ..., EFASA 2010 leadership have participated in presenting relevant scientific papers, shared their experiences in curriculum development and provided their commitment to the continued support of the program in teaching, research and other scientific and technical supports.
EFASA has also launched its website with very basic information such as the list of members together with their emails and telephone numbers to facilitate horizontal communication, proceedings of the First National Conference held at Zwai and the abstracts of this BahirDar conference. This website can be accessed by the abbreviated name of the association and admittedly requires a lot of inputs to really portray the actual face of EFASA and its intentions that reach out to national and international issues.
Despite these and other great successes, EFASA, as it is so young, faces problems in establishing an office, and employing personnel who can handle the paper work. This burden is borne at present by the office bearers, which quite honestly is taxing a lot of their time.
In all its efforts EFASA is not alone. The assistance it obtains from Addis Ababa University, where it sits, and the Biological Society of Ethiopia, and many others is such a force that EFASA could not have made it alone. This year the technical and financial support EFASA obtained from the following government and international organizations is highly appreciated. These are:
1. The Amhara Bureau of Agriculture and Rural Development, Rural Capacity Building Project, Bahir Dar 2. The Amhara Regional Agricultural Research Institute, ARARI, Bahir Dar 3. Food and Agriculture Organization Sub-Regional office for Eastern Africa, Addis Ababa 4. Bahir Dar Fisheries and Aquatic Life Research Center, Bahir Dar 5. Development Partnership in Higher Education (DelPHE), Department for International Development (DIFD) and the British Council, UK 6. Ambo University 7. Haramaya university 8. Addis Ababa University 9. The Ethiopian Quality Standards Authority, Addis Ababa 10. The Ethiopian Agricultural research Institute (EAIR) 11. and others like Ato Mulat Basazinew, who is supplier of fishing gears. EFASA also extends its acknowledgements to the Regional and Central Organizing Committees composed of
1. Ato Alayu Yalew, and 2. Ato Belay Abdissa from Bahir Dar Fisheries and Aquatic Life Research Center, 3. Dr. Ayalew Wondie from Bahir Dar University, and 4. Ato Chalachew Argaw from the Bureau of Agriculture and Rural Development. 5. Ato Ashagre Gibtan, Department of Biology, AAU, PhD candidate 6. Ato Akewak Geremew, Department of Biology, AAU, PhD candidate
EFASA is really proud to have such dedicated members on whom it can always count on and whose examples it believes will be picked up by many organizers to come, as today they have set the pace on which we have always to build on.
Dear conference participants!
Please allow me to inform you that
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Ma nagement of shallow water bodies ..., EFASA 2010
1. This conference has such a crowded schedule that all paper presenters and moderators will have to stick to the time schedule. 2. All participants keep in mind that the decision reached at Zwai last year to invite the farming community to our conference and make our presentations in the language they understand prevails, while still the transparencies are in English. Last but not in any way least, I must seize this opportunity to thank the Executive Committee members of EFASA who always came to meetings, shared their views at critical moments of decision making and made their time available for EFASA’s activities. I also seize the time to thank our honorable guests Ato Alemu Admas and Ato Tesfaye Mengist and all conference participants for coming here despite your busy schedules and for giving me your time to listen to this speech.
Thank you all so much!!!
Brook Lemma, Dr. President of EFASA Bahir Dar 21 February 2010
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Ma nagement of shallow water bodies ..., EFASA 2010
Keynote address by Representative of the Bureau of Agriculture and Rural Development of the Amhara Regional State
• Excellencies, • Distinguished Participants, Ladies and Gentlemen,
I am pleased to welcome all of you to Bahir Dar town on behalf of myself and the BoARD of the Amhara National Regional State. First and foremost, I would like to thank Dr. Brook Lemma, President of EFASA for his kind invitation to me to attend and deliver a keynote address at this very important conference. My keynote address will focus on extension intervention in Amhara Region in general and an overview of fisheries and aquaculture in particular. The Federal Government of Ethiopia had initiated the Agricultural Development -led Industrialization (ADLI), the Plan for Accelerated and Sustainable Development to End Poverty and the Sustainable Development and Poverty Reduction Program. These are pillars of our agricultural development policy at national level. Agricultural extension intervention was started in Ethiopia in 1953 following the establishment of the Imperial Ethiopian College of Agriculture and Mechanical Arts, currently named Haromaya University, assisted by Oklaboma State University of the United States of America. The college was given the mandates of conducting teaching, research and extension activities. The objectives of the extension activity were to transfer the research outputs, import and introduce technologies and improved agricultural practices to farmers. In 1963, the mandate of agricultural extension was transferred to the then Ministry of Agriculture and posted as a department at a national level and extension supervisors assigned at provincial level. Currently, during the first 4 years after the change of Government in 1991, the previously started extension services under PADEP programmes have continued. Meanwhile, a critical evaluation and review of the past extension approaches was done in order to develop a new extension system for the country. As a result, new extension system called Participatory Demonstration and Training Extension System (PADETES) was developed in 1995 based on the Agricultural Development-led Industrialization (ADLI) strategy formulated by the FDRE in 1993. This extension system is the first of its kind in the country’s extension history to be developed by the Government without foreign assistance. The main features of PADETS include:- • Increasing production and productivity of small-scale farmers through research generated information and technologies. • Empowering farmers to participate actively in the development process. • Increasing the level of food self-sufficiency. • Increase the supply of industrial and export crops. • Ensure the rehabilitation and conservation of natural resource base of agriculture. • Encourage farmer's organization. To address the farmer's need and farming system and also to utilize the potentials of the different agro-ecologies, three divisions (teams) are organized under the Agricultural Extension Department at Federal level. These are:- • Moisture reliable areas Extension Division. • Moisture un-reliable areas Extension Division. • Pastoral areas Extension Division. To conclude, in the history of Ethiopian agriculture, various extension intervention programs have been implemented in the form of fully-fledged programs or as pilot projects. Unfortunately, the impacts of all of these development interventions were not that much significant in terms of improving the life of the rural population in general and the mode of farming and productivity in
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Ma nagement of shallow water bodies ..., EFASA 2010 particular. It is only recently especially after the introduction of PADETES that interventions began to penetrate into rural areas with the aim of improving the ’s lives.. Based on the 2007 census conducted by the Central Statistical Agency of Ethiopia (CSA), the Amhara Region had a population of 17,214,056 of whom 8,636,875 were men and 8,577,181 women; urban inhabitants number 2,112,220 or 12.27% of the population. With an estimated area of 159,173.66 square kilometers, this region has an estimated density of 108.15 people per square kilometer. The CSA of Ethiopia estimated in 2005 show that farmers in Amhara had a total of 9,694,800 head of cattle (representing 25% of Ethiopia's total cattle), 6,390,800 sheep (36.7%), 4,101,770 goats (31.6%), 257,320 horses (17%), 8,900 mules (6%), 1,400,030 asses (55.9%), 14,270 camels (3.12%), 8,442,240 poultry of all species (27.3%), and 919,450 beehives (21.1%). The potential of fishery and aquaculture in the region is very high. In the rivers and lakes alone, we can produce about 26, 000 tons per year. As far as fish farming is concerned, the lands and the waters of the Amhara National Regional State (ANRS) are very favorable to expand fish farming from cold to warm water fish species. The Region’s standing surface water resources, comprised of many ponds, reservoirs constructed for irrigation and power generation, and lakes, can provide numerous opportunities for fish farming throughout the regional state. For fish farming, we need land and reliable water and labor. We have all these inputs in our region. There are many big rivers, lakes and man-made lakes in the region. Among the known rivers: Abay, Tekez, Angereb, Shinfa, Guang and Ayma rivers have a diversified fish fauna including Nile Perch. Lake Tana has an area of 3500 km 2. It is the largest lake in the country and situated in the north- western highlands at the altitude of approximately 1800 m. Several rivers enter the lake; Gumara, Rib, Little Abay, Arno Garno. Megech, Dirma, etc. The Blue Nile is the only outflow. After 30 km, this river plunges down 40-meters-high water falls, isolating Lake Tana and its tributaries from other parts of the Nile basin. The fishery on Lake Tana is characterized by a specific combination of gears and fishing crafts. Presently the most frequently used fishing gears are gill nets, scoop nets, traps, cast nets and hooks. Of the total fish production in 2000 Eth.C, 8.42 million Birr was generated from export market and 51 million from domestic market. Total income from the sales of fish generated for the region was 59.4 million. Therefore, the contribution of fisheries to the regional GDP is encouraging. Our objective for expanding aquaculture is to improve food and nutritional security of the large segments of the rural poor communities. Fish farming in the region started 7 years ago. The result so far is very encouraging. We have about 300 fish farmers in the region. But shortage of fish seed is becoming a limiting factor. The regional government is very much interested to establish one government fish hatchery and we are seeking technical and financial support. For sustainable development of fisheries and aquaculture, the The Amhara National Regional State has issued the policy instruments for the benefit of the present and future generations' fishers in the Amhara National Regional State. There are also, many investment incentives for the investor to enter this business. The Amhara National Regional Government encourages the private sector to participate in aquaculture and fishery investment. EFASA is a professional and technical association composed of scientists, fishery officers, extension workers and non-governmental organizations. The Government’s interest both at federal and regional level is to develop this sector so that it will play its part for agricultural development. However, to develop this sector, BoARD is very much willing to collaborate technically with EFASA in order to solve the increasing problems of our fisheries and aquaculture development. We know that EFASA may have great opportunity to contact national and international organizations in terms of fisheries and aquaculture. We are very hopeful that this professional association will promote our fisheries and aquaculture development effort and provide solutions for its constraints. Finally, I would like to once again thank EFASA for giving me the opportunity. My vision is to see EFASA as an association that will deliver appropriate development support for the policy makers and
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Ma nagement of shallow water bodies ..., EFASA 2010 also to serve as a vehicle to connect the three pillars of development (Teaching-Research and Extension). Thank you and I wish you a successful conference and a wonderful stay in Bahir Dar.
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Ma nagement of shallow water bodies ..., EFASA 2010
Opening speech by the Deputy Head of the Bureau of Agriculture and Rural Development of the Amhara Regional State
• Dear Ato Tesfaye Mengist, • Process Owner for Extension, Bureau of Agriculture and Rural Development, Bahir Dar, • Dear Dr. Brook Lemma, President of the Ethiopian Fisheries and Aquatic Sciences Association (EFASA), • Dear invited guests, • Conference participants, • Ladies and Gentlemen.
I feel very much honored to be invited here at this august second national conference of the Ethiopian Fisheries and Aquatic Sciences Association (EFASA) to be held here in Bahir Dar as of today 20 to 21 February 2010. It is also a landmark opportunity to have with us representatives of Development of Partners for Higher Education (DelPHE), the Department for International Development (DFID) and the British Council of the United Kingdom who as major stakeholders join us at this conference signifying that what we do here at Bahir Dar has international importance.
The Amhara Bureau of Agriculture and Rural Development highly appreciates what EFASA is doing as it moves annually from one center of focus to the other to promote knowledge and technology generated by researchers, extension agents and farmers engaged in fisheries and aquatic sciences. My office took this as a great opportunity to express the commitment it has to the field and has supported the organization of this conference so that it has arrived to this successful day that has brought us all together.
As I have learned from the conference program and the book of abstracts handed out by the organizers, that there are a wide range of papers that are going to be presented that include fishes and fishery practices, recent developments in aquaculture, fishery products marketing and the associated problems, fishery policy issues, and aquatic sciences papers. These interactions in the coming two days will get a lot of information across not only to the scientific community but also to policy makers, fish market agents, farmers and extension agents who reach out always to assist the community in its fight against food insecurity and reduction of poverty. I also believe that the scientific community here in this hall and elsewhere in the world will get added value through the media and the web to go further in researching new unexplored grounds of fishes, fisheries and aquatic sciences.
My Bureau has learnt that EFASA being a young association of only two years of service has made great achievements in addressing this sector of national development, which has been neglected for so long. Today, the days are gone in the Amhara Region when water and the associated resources were believed to be inexhaustible and always resilient to absorb all the wastes we dump in them. The farmers in the region have developed the technology not only to harvest and wisely use water but also put some fish seeds in them to feed their children and make some supplementary incomes to support their families. This is made possible through the relentless efforts of the regional administration that always generates the right decision at the right time, the efforts of the scientific community that provides us with the usable data and the extension workers that turn science into action and more knowledge by building aquaculture capacity in the farming community. This is for me and my colleagues in the Bureau a noble addition to the efforts made to reduce poverty and build on food security for the general public. During your excursion, I hope you will have the opportunity to visit the ponds managed by farmers, the associated technologies and the bright future the farmers envisage from the aquaculture practices they are embarking on as part of their integrated farming system.
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Ma nagement of shallow water bodies ..., EFASA 2010
Dear conference participants! I realize that you have come a long way from different parts of Ethiopia and also from around the world, despite your other duties and responsibilities that are of equal importance. This very clearly demonstrates the commitment you have to the development of the sector and the emergence of the Ethiopian people with success from poverty and problems of food security. I would also like to take this opportunity to convey to you that during these two days of the conference, my Bureau and the Amhara Regional Administration will provide you all the support you need to ensure that your deliberations come to successful completion as you have planned it when you left home to come here.
With these short remarks and with all the confidence I have that you will deliver the job ahead of you with great success, I declare this conference on "Management of shallow water bodies for improved productivity and peoples' livelihoods in Ethiopia " open.
Thank you!
Alemu Admas Deputy Bureau Head, Bureau of Agriculture and Rural Development, Bahir Dar
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Ma nagement of shallow water bodies ..., EFASA 2010
Part one Oral Presentations
Current land use practices and possible management strategies in shore area wetland ecosystem of Lake Tana: Towards improving livelihoods, productivity and biodiversity conservation
Ayalew Wondie (PhD), Bahir Dar University
ABSTRACT : This paper presents the current status of Lake Tana buffer zone based on research outputs and field observations. 6% of the earth’s surface is wetlands (Maltby, 1986, WCMC, 1992). 1% (345,000 km 2) of Africa’s landscape is covered by wetlands (Finlayson and Moser, 1991). Besides theirs multifunctional values, wetlands are the most productive ecosystem in the world. For example papyrus in tropical Africa can produce 143 tonnes/hectare as compared to maize and sugar cane (60 -70 t/ha). In Ethiopia, wetland covers about 2% (13,699 km 2) /Tesfaye 1990, Hillman and Abebe 1993/. With the exception of coastal and marine related, all forms of wetlands are represented in Ethiopia. More than 50 % of these wetlands are major lakes (7,444 km 2) and the rest are swamps and marshes. Lake Tana as a wetland is one of the largest and rich in biodiversity . In this paper, habitat characterization and mapping of the shore area of the lake were made on the basis of land use and vegetation cover. Area percentage/coverage of each habitat in the shore area of the lake weres assessed. Quadrants were used to quantify the major plant species. Major macrophyte types both at community and species level were determined. Four major habitats were identified based on land use and nature of the landscape. The first is sand beach which is dominated by sand mining, fish landing sites and pasture land. Secondly, rocky shore area with forest dominated by horticulture, fishing, fuel wood, and monastery. Thirdly, farm land including sediment loaded river mouths dominated by Teff cultivation. The last one is urban shore area which is characterized by shoreline recreation, boating and manufacturing. Three dominant plant communities were identified so far throughout the shore area of the lake, namely tree (e.g. Syzgium guineense) and shrubs dominated in rocky shore areas, Scirpus and Potamogeton species dominated in the north and east shore area, and Cyperus and Typh a dominated in the southern gulf shore area of the lake. About 50 major plant species were identified. Herbaceous plants showed a zonation of vegetation along a hydrological gradient from emergent plants at the water/land interface to rooted, floating-leaved and then submerged plants at the interface between the swamp and open water. The ecotones between lakes and terrestrial ecosystems are crucial for protection of the lake ecosystem against anthropogenic impacts. The transition area has the same function for a lake as the membrane has for a cell: it prevents, to a certain extent, penetration of undesirable components into the lake. The most outstanding threats to Lake Tana shore areas stability are agriculture, industrial pollution, and over-harvesting of wetland resources. Therefore, it is crucial to preserve the shore ecotones around the lake and the wetlands in the watershed as well. There is a need to develop integrated aquatic farming systems with emphasis on local knowledge so as to improve food security and livelihoods.
Key words : Biodiversity conservation, Lake Tana, land use, shore areas, wetlands.
Introduction Wetlands comprise 6% of the earth’s surface (Maltby, 1986; WCMC, 1992). 1% (345,000 km 2) of Africa’s landscape is covered by wetlands (Finlayson and Moser, 1991). Besides their multifunctional values, wetlands are the most productive ecosystem in the world. For example papyrus in tropical Africa can produce 143 tonnes/hectar as compared to maize and sugar cane (60 -70 t/ha). In Ethiopia, wetland covers about 2% (13,699 km 2) /Tesfaye 1990, Hillman and Abebe 1993/. With the exception of coastal and marine related, all forms of wetlands are represented in Ethiopia. More than 50 % of these wetlands are major lakes (7,444 km 2) and the rest are swamps and marshes. Healthy ecosystems are a fundamental requirement for sustainable development and biodiversity conservation. Biological resources support human livelihoods, and make it possible to adapt to changing needs and environmental conditions. Wetland livelihood systems provide multiple services, satisfying the needs of the local community while providing fundamental ecological services for the
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Ma nagement of shallow water bodies ..., EFASA 2010 larger catchment population. Fishery, livestock husbandry, small scale agriculture and wetland biomass harvesting are the main livelihood activities for people living in river and lake regions. The ecotones between lakes and terrestrial ecosystems are crucial for protection of the lake ecosystem against anthropogenic impacts. The transition area has the same function for a lake as the membrane has for a cell: it prevents, to a certain extent, penetration of undesirable components into the lake. The trade-off between environmental protection and development is most acute in fragile ecosystems such as wetlands. Wetlands are of value because they play an important role in maintaining environmental quality, sustaining livelihoods and supporting biodiversity. However, recently the wetland biological resources have been severely affected due to both natural and human elements, resulting in a decline of the wetland system’s ecological functions and self-restoration ability. This decline is associated with a decrease in the area of the body due to sedimentation, local water pollution, and a general reduction in biological quality. Furthermore, demographic changes and increasing poverty have led to more invasive activities which have damaged the overall resource values. Nowadays, rain-fed agriculture is increasingly unreliable due to erratic rainfall. Therefore, poverty related pressures; encroachment and misguided development schemes have led to environmental degradation that has compromised basic ecosystem services (e.g. fish habitat, chemical and sediment retention). If this trend continues, the future livelihoods and food security of millions of people is at risk. Lake shore areas are highly productive and their macrophytes are a very important component in the trophic structure of lakest. In addition, macrophyte vegetation serve as ecological buffer zone which moderate changes in the shore area of the lake by regulating nutrient, sediment flow and recycling. The various macrophyte species in the shore areas are not distributed at random; each has its microhabitat, especially on water level gradient. This study aimed to investigate the status of Lake Tana shore area in terms of land use and biodiversity so as to evaluate the loss of functions and services in the system.
Objectives The general objective is to assess the current status of Lake Tana shore area in relation to land use activities so as to evaluate the changes of buffering functions associated with threats to the wetland resources and recommend appropriate management options. The specific objectives are: • To characterize/classify/ specific habitats on the basis of land use and nature of the landscape throughout the whole lakeshore, • To map the area coverage of each habitat in the lake shore area, • To identify major macrophyte types both at community and species level, • To identify zonation of aquatic vegetation along a hydrological gradient, and • To identify major anthropogenic threats and impacts in the lake shore area.
Materials and methods Description of the study area : Lake Tana, Ethiopian’s largest lake is geographically situated in the northwestern highlands of the country and is the origin of the Blue Nile. It was formed from blocking of volcanic activity in the upper Blue Nile. Lake Tana is a shallow, turbid, mixed and meso- oligotrophic lake. About 65% of the catchment is seasonally flooded extensive wetland. The catchment area of the lake has a dendritic type of drainage network. Five major permanent rivers, Gelgel Abbay (Small Blue Nile), Gumara, Rib, Megech and Dirma, as well as more than 30 seasonal streams feed the lake, whereas the Blue Nile River is the only outlflow from Lake Tana. Lake Tana has emerged as one of the global top 250 lake regions most important for biological diversity (Lakenet, 1999). The lake and its catchment is known for its rich biodiversity, suchas more than 300 bird species (Shimelis Aynalem, date; Nega Tassie, date; Negash Atnafu, date); above 26 species of fishes (de Graaf,date; Abebe Getahun, date; Eshetie Dejen, date); 85 and 25 species of
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Ma nagement of shallow water bodies ..., EFASA 2010 phytoplankton and zooplankton, respectively (Ayalew Wondie and Seyoum Mengestou, 2006; Eshetie Dejen, 2004). It is also a major world cultural and archaeological site. Moreover, the catchment has critical national significance as growth corridor in the region and the country as well. These include vast water resources potential for irrigation; enormous potential to develop hydroelectric power (including export to neighboring countries); rich potential for development of high value crops such as rice and livestock production; high potential for ecotourism and other livelihood strategies outside farming. In the last two decades, human population pressure associated with climate change and merging development schemes, the lake have shown a decline in its wetland system’s ecological functions and self-restoration ability. Besides agricultural and urbanization impacts, the interest for hydropower and irrigation started during the construction of regulatory weir of chara chara at the outlet, and has then proceeded by diversion of Tana-Beles (operation stage) and damming of inflowing rivers such as Megech, Rib and Gumara ( projects undertaken). The commercial fishery consists of an endemic flock of large Labeobarbus spp. (Cyprinidae), Oreochromis niloticus (Cichlidae), Clarias gariepinnus (Clariidae) and Varicorhinus beso (Cyprinidae). In Lake Tana, fishery activity is highly affected by habitat degradation as compared to resource depletion Sampling and data collection: The study was conducted during both dry season (April–May 2008) and wet season (October–December 2008). On the basis of landscape type and land use activities, four major habitats were selected. Water level, water transparency and nutrient concentration were measured during sampling period. In addition, temperature, conductivity and dissolved Oxygen concentration were measured. Habitat area coverage in percent was delineated using Google earth satellite image and evaluated by ground observation during field survey with GPS. In total, 4 habitat zones (16 transects) were identified based on land use and nature of landscape along the lake. (1) Sand beach dominated by sand mining, fish landing sites and pasture land. (2) Rocky Bank: shore area forest dominated by coffee, fishing, fuel wood, and monastery.(3) Muddy Bank ( farm land): including sediment loaded river mouths dominated by pastureland, Teff and Maize cultivation. Vegetation type is more of annual and exotic weeds. (4) Urban shore area characterized with various shoreline developments such as recreation, boating and manufacturing . Zonation of aquatic vegetation along a hydrological gradient was estimated using field site observation. Macrophytes were photographed by digital camera in the field and species identification was made using standard keys (Prescott 1962). Questionnaire interview, focus group discussion and personal observation were employed to understand the perception of local communities (farmers, fishers, etc), shoreline developers, extension agents and local governors on the level of degradation and its impact in the shore area. Factors such as age, level of education, absence/presence or size of farmland, number of livestock and household size were considered in the analysis. Sampling procedures and sample sizes were made considering nature habitat and vegetation community type and but not political boundaries such as zones, woredas and kebeles. Multistage purposive samplings, which represent each of the major livelihood system, was made as follows (Table 1).
Table 1 : Sampling procedures and sample sizes for socioeconomic survey in the study area
Representative Livelihood/occupation Sample size/respondants/ Habitat sites in a habitat category in each site in each category Delgie Farmers 10 Fishers 5 Extension agents 2 Local governors 2
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Representative Livelihood/occupation Sample size/respondants/ Habitat sites in a habitat category in each site in each category Sandy Enfranz Farmers 10 Fishers 5 Extension agents 3 Local governors 3 Rocky Zegie Farmers 8 Fishers 5 Extension agents 2 Local governors 2 Dengel Ber Farmers 8 Fishers 5 Extension agents 2 Local governors 2 Korata Farmers 8 Fishers 5 Extension agents 2 Local governors 2 Muddy Dembia shore Farmers 10 area Fishers 7 (Dirma-Megech Extension agents 4 watershed) Local governors 4 Fogera shore area Farmers 10 (Rib-Gumara Fishers 7 Watershed) Extension agents 4 Local governors 4 Gelgel Abbay Farmers 10 shore area Fishers 7 Extension agents 4 Local governors 4 Urban Bahir Dar City Shoreline developers 10 City administration 5 Relevant governmental institution 5
Results and discussion
Habitat characterization : Three habitats which have distinct characteristics were identified. Sand beach dominated by sand mining, fish landing sites and pasture land. Rocky Bank: shore area forest dominated by coffee, fishing, fuel wood, and monastery. Urban shore area was also included. Muddy Bank (farm land): including sediment loaded river mouths dominated by pastureland, Teff and Maize cultivation. Vegetation type is more of annual and exotic weeds (Fig 1).
Dirma R. Dirma Delgi Gorgora R. Megech Arno-Garno R.
Lake Tana Rib R.
Dek Gumera R. Kunzila
Gelda R. . R y a Zegie b A l e g l e B G lu e Ni le Bahir R. 10 km Dar
Fig. 1: Map showing habitat characterization of Lake Tana shore area
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Shoreline vegetations and other communities: Three dominant plant communities were identified throughout the shore area of the Lake Trees (e.g. Syzgium guineense) and shrubs dominated in rocky shore areas, Scirpus and Polygonum species dominated in the north and east shore area, and Papyrus and Typha dominated in the southwestern gulf shore area of the lake (Fig. 2).
Fig. 2 . Characterization of Lake Tana shore area by their dominant vegetation communities
A total of over 50 macrophyte species belonging to over 15 families were recorded in Lake Tana shore area (Table 2). Only 2 submerged and floating macrophytes and 15 emergent ones were recorded in the northern part (8 transects) of the lake. 3 and 10 more species of submerged and emergent species were recorded in the south western zones, respectively. Therefore the southwestern zone is found to be in a better condition as compared to northeastern zone. This is because of population pressure and accessibility of infrastructures which results in overall degradation of the environment. Among environmental variables, water turbidity (clarity), lakewater level, turbulence and nitrogen concentration were the most important (Table 2). In Lake Tana water level from the shore area declined during dry season exposing 0.5–1 km shoreline from the lake. During this season, exposed soils were cleared of emergent vegetation and used for agriculture. In spite of their dynamics in abundance and diversity with seasonal changes, macrophytes are quite different in substratum selection. The survey indicated most submerged macrophytes grow in the south-western part of the lake where there is no wind current and urban fringes. Similarly in Lake George, papyrus formed large fringing floating swamps, and flourished in water with conductivity of 200 µS (Maclean, et al., 2004).
Table 2 : Mean spatial and temporal variations in physico-chemical parameters of Lake Tana and emergent, submerged and floating shore areas.
Wet season Dry season Parameter Z K DM RG GA D BD Z K DM RG GA D BD Temp. ( 0c) 22 23 25 24 23 26 24 23 24 26 24 24 26.5 24 Depth (m) 0.5 0.6 0.4 0.3 0.8 0.6 0.7 0.4 0.5 0.2 0.1 1.4 0.4 1.2 DO (mg/l) 4.0 4.5 3.5 3.6 5.0 4.4 3.8 5.0 5.8 3.7 3.9 5.5 4.6 4.0 Cond. 201 228 241 245 251 230 287 198 220 233 244 250 235 289 (µS/cm) pH 6.8 6.5 7.1 7.3 7.8 7.0 6.5 6.7 6.8 7.3 7.4 7-6 6.9 6.9 SRP 0.8 0.7 0.6 0.7 0.9 0.6 0.9 0.9 0.95 0.6 0.5 0.7 0.5 0.7 NO 3-N 0.7 0.6 0.9 0.8 1.5 0.9 1.2 0.6 0.4 0.4 0.3 0.8 0.5 1.0 Legend: Z-Zegie, K-Korata, DM-Dirma-Megech shore area, RG- Rib-Gumara shore area, GA- Gilegel Abbay, D- Delgi, BD- Bahir Dar City
Since there was no significant spatial difference in the major physico-chemical parameters among different sies of the lake water; habitat substratum and land use activities were considered the major
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Ma nagement of shallow water bodies ..., EFASA 2010 operators. In spite of the limited presence and number of the submerged and floating macrophytes recorded, they are quite different in their habitat selection. For example, Ceratophyllum species is foundt throughout the lake shore, as it has wide range of tolerance while Nymphea species grow best in habitats that are wind-protected (calm condition), shaded and higher clarity areas. In shallow calm parts in the shore area of the lake, especially at the river mouths, head of blue Nile river and pocket sites at the west zone, Pistia spp ( water lettuce) and Sagittaria spp (common arrowhead) are common. The occurrence and abundance of Scirpus spp in the north and east habitats is becausethis species is known to be tolerant of shallow water and waterlogged soils as compared to Typha and Cyperus sp. Water level fluctuation is considered by many authors ast the most important factor that controls the distribution of shoreline and aquatic vegetation (Springuel et al. 1990, 1991; Ali, 2004). The present study also revealed that these same factors play, together with anthropogenic activities, an important role in governing the distribution of the shoreline vegetation. In Lake Tana aquatic ecosystem, it appears that stress to macrophytes is produced by high turbidity due to sedimentation process and direct conversion of shore areas to agricultural and other purposes. In addition, population pressure, low level of awareness, lack of wetland regulation and enforcement are othert important factors. Zonation varied both spatially and temporally. During dry season where water level declined and water clarity increased, the zonation from deep water was Nymphacae – Potomageton and Ceratophyllum – emergent vegetation (e.g. papyrus). Papyrus and other emergent plants were floating on the surface even in the deep-water zone (Fig 3).
Fig. 3 : Vegetation zonation of the fringes of Lake Tana
Socioeconomic survey results showed a high concern among older respondents and positive perception about lake shore conservation, although they are ignorant about zonation of buffer zone and their ecological role. Surprisingly, birds and other wildlife were considered as pests, especially by the younger generation. This is because more than 50% of the young (below 30 years) were landless and have keen interest to exploit whatever opportunities were present in the lakeshore wetlands. Fishers have better perception towards the cause for the decline of their fish resources (Tilapia and Labeobarbs ) its habitat alteration (60%) when compared to fishing technology (30%), marketing (10%). However, less priority and attention were given by local governors and extension agents to the management of the lake and shore area vegetation as well. Even in most woredas, the local administrators distributed the buffer zone and grazing areas to landless young people.
Conclusion
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In general, threats to Lake Tana shore areas stability are agriculture, industrial pollution, and over- harvesting of wetland resources. Two decades ago, papyrus completely encircled the lake. In addition to poor linkage among institutions and lack of coordination, limited capacity to manage and monitor project and programme activities, the fast growing towns associated without appropriate waste disposal systems and the low regeneration capacity of the inflowing rivers to neutralize toxicity or dilute the waste material (due to low volume of rivers) has increased the threats that endanger t the lake resources. The overall input and output of the system can be shown with the following diagram (Fig. 4).
Social pressures •Population growth rate •Fallacy of policies and institutional supports •Subsistence economy system •Poverty
Center of gravity Natural •Extensive vulnerability Feature of the lake inflowing rivers •shallow •low in productivity •Multipurpose •Migratory nature •Rich in biodiversity •upstream Deforestation •Waterborne •Rich water sources (rivers, •Downstream diseases streams, lake, rain and ground sedimentation sources)
Consequences •Significant loss of species •Loss of productivity •Poverty and social chaos •Affected natural cycles of ecosystem elements (e.g., breeding, nursery)
Fig. 4 : Conceptual framework and its consequences in Lake Tana ecosystem.
Recommendations • Monitoring of vegetation communities with a high degree of ecological preservation is needed. o Change in land use/cover using remote sensing and GIS analysis o Detailed field survey/inventory on biodiversity and socioeconomic activities • Encourage already existing knowledge through promotion of wise use utilization vs conservation. • Support developmental research which will be bring environmentally friendly investment i.e alternative livelihoods such as finger pond farming, cage culture, forage harvest. In general, need to develop integrated aquatic farming systems. • Use of opportunities such as the positive attitudes of the elders, fishers and irrigation associations, graduate research, civic societies (e.g. EFASA) and current higher global attention to the environment to develop management tools.
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• An integrated watershed management approach of the lake and its surroundings rather than focusing only on the lake; an integrated watershed management is good opportunity to apply the win-win approach. • Lake Tana is the home to commercial fish and globally threatened intact flocks of cyprinds. Currently the lake supports dense and poor local communities. The efforts needed to meet the needs of an additional million people over the next decades will be immense. The water level of the lake over the last 10 years has dropped by about 1-2m.This condition (not invasive water hyacinths) has caused difficulty to shipping and the fishing industry. Furthermore, the high silt load has had noticeable impact. • It is clear that the development of the lake's resources can only be meaningful and sustainable when the following principles are met: precaution, prevention, integration and public participation . We have to work together to increase awareness of the costs of inaction i.e. of the price economies to be paid for lax environmental management and ecological degradation. • A number of potential management and policy challenges may significantly affect the aquatic system and fisheries in the lake. Measures to try to restore and stabilize the fish ecology in the lake might have unforeseen effects, because the huge, complex ecosystem is not understood completely. Attempts to develop innovative aquaculture, dams, irrigation and hydropower schemes might have unforeseen effects on the ecosystem, as did the introduction of exotic species in the past. The scale of any proposed aquaculture needs to be limited until the requirements and impacts of the system are well established.
Acknowledgments I acknowledge the Ministry of Science and Technology for funding this research, Bshir Dar Water Resources Bureaus and Bahir Dar University.
References Ali, M (2004). Aquatic and shoreline vegetation of Lake Nubia, Sudan. Acta Bot.Croat . 63 (2), 101-111 Biswas, A.K. (1991). Effective monitoring of lake waters. In: Guidelines on Lake Management, Volume 2: Socio-Economic Aspects of Lake Reservoir Management, Hashimoto, M., and Barret, B.F.D., eds. Otsu, Japan: International Lake Environment Committee and United Nations Environmental Program. International Water Management Institute, IWMI (2008). Improved water and land management in the Ethiopian highlands and its impact on downstream stakeholders dependent on the Blue Nile. Working paper. Maclean, I.M.D., M. Hassall, R.Boar, R. and O. Nasirwa. (2003). Effect of habitat degradation on avian guilds in East African papyrus Cyperus papyrus L.swamps. Bird Conservation International, 13: 283-297. Springuel, I., M.M.Murphy, K.J., (1990). Aquatic macrophyte growth in relation to water level regime in the river Nile and its impoundments in Upper Egypt. Proc.8 th Symp. on aquatic weeds. Europ. Weed Res. Soc ., Uppsala, 199-201 Springuel, I., EL-Hadidi, M.M. (1991). Vegetation gradient n the shore of Lake Nasser in Egypt. Vegetation 94:15-23. Zinabu, Gebre Mariam, (1994 ). Long-term changes in indices of chemical and productive status of a group of tropical Ethiopian lakes with differing exposure to human influences . Arch. Hydrobiol . 132:115-125.
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Enhancing wetland ecosystem services through engineering intervention: A management plan for treatment of municipal wastewater, Bahir Dar Gulf of Lake Tana, Ethiopia
Goraw Goshu, Amhara Regional Agricultural Research Institute. E-mail: [email protected]
ABSTRACT : Design of natural wetland that receives influent of Bahirdar municipality, near Saint George church, Bahirdar gulf area was done to enhance the inherent capacity of the wetland for treating waste water. Free water surface constructed wetland (FWSCW) - first order decay model was used to design constructed wetland mainly for removal of pathogens (FC), total nitrogen (TN), total phosphorous (TP), and total 0 suspended solids (TSS) and biological oxygen demand (BOD 520 C). Maximum concentrations of log 6 CFU per 100 ml of FC, 41 mg/L of TN, 1mg/L of TP, 405 mg/L of TSS and BOD 5 values of 300 mg/L recorded in the peak rainy season and an annual waste water discharge of 696 m 3 per year were considered for design purposes. FWS- CW having an area of 68 m 2 and a wetland aspect ratio of 2:1 will have expected performances (removal efficiency) of 99.9 % for FC, 76 % for TN, 90 % for TP, 93 % for TSS and 90 % for BOD 5 respectively. It is recommended that similar engineering interventions should be done to take advantage of the enhanced wetland ecosystem services to treat point sources of pollution in Bahirdar gulf of Lake Tana in particular and the country at large, and realize achievement of MDG of environmental sustainability .
Key words : Bahir Dar gulf, ecological engineering, ecosystems biotechnology, tropical area, wastewater treatment .
Introduction Constructed wetlands are engineered systems that have been designed and constructed to utilize the natural processes involving wetland vegetation, soils, and the associated microbial assemblages to assist in treating wastewaters. They are designed to take advantage of many of the same processes that occur in natural wetlands, but do so within a more controlled environment (Vymazal, 2005). Constructed wetlands include FWS, as well as the more recently developed subsurface flow systems (SFS). The latter systems involve subsurface flow through a permeable medium. In Europe, free water surface constructed wetlands (FWS-CW) are the oldest designs and the most common systems are designed with horizontal sub-surface flow (HF-CWS) (Brix, 1994, Vymazal 2001a) but vertical flow (VF CWs) systems are getting more popular at present. Nevertheless, FWS-Cw design was considered due to, among others, the cost and lack of technical know-how of the current designs in Europe. The general concept behind free water surface constructed wetlands (FWS - CW) involves the treatment of waste water using constructed wetlands of free water surface (FWS) type, in order to eliminate the pathogens (FC), biological oxygen demand (BOD), and suspended solids (TSS) that are contained in the waste water. The different parameters being used in FWS, basically focus on efficiently removing the pathogens and stripping inorganic nutrients so that the water become less harmful for the lake ecology as well as for other uses. As the water flows through the medium, it will be purified during contact with the wetland components . Wastewater treatment although important from public health, ecological, aesthetic and other points of view, is generally given a low priority, especially in developing countries where there are many competing demands on the limited funds for development. High cost of construction and maintenance of sewage treatment plants is a deterrent factor (Shinny, et al., 2004). For many years natural water bodies, particularly wetlands, have been used as disposal for waste water, taking the advantages of the natural capacity of this system to treat the water, but uncontrolled discharge have caused low efficiency, pollution and finally to disappearance of many wetlands. Most of the untreated wastes find their way to the nearest water source. Constructed wetlands can be a good solution to pollution problems, both in terms of treatment of waste water and avoid pollution of the natural environment. The harmful effects of chemical treatment also make ecological alternatives attractive
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There are some waste stabilization ponds constructed to treat effluents of some industries at a national level. However, these systems are not performing efficiently and sustainably, among others, escalating costs of operation. Moreover, the enforcement mechanisms from environmental authority side are not as expected. The practice and idea of treating wastes with very cheap natural systems of wetlands is generally lacking in Ethiopia and is poorly reported. The Lake Tana environments are under growing stress from point and diffuse sources of pollution, and especially, the largest share of pollution comes from Bahirdar city since it has no centralized sewerage system and most of the sewerage lines have been directed to the lake. The wastewaters released from Felegehiwot hospital and from the municipality near St.George are major public health risk factors as substantial amount of vegetables supplied for the city are grown using this untreated water. Therefore, the general objective of this study was to propose a management plan for the treatment of waste water near St. George, Bahirdar gulf of Lake Tana through the implementation of a FWS constructed wetland. The specific objectives are 1) to design a FWS constructed wetland that can treat the water II) to remove pathogens from waste water and use the water for irrigation III) and to remove organic matter and nutrients from entering lake Tana thereby reducing eutrophication and ensuring environmental sustainability, and IV) To establish a model FWS-CW.
Materials and methods General description : The FWS-CW was deigned to enhance the inherent ecosystem services of wetlands in the shore areas of southern part of Lake Tana, Bahirdar Gulf area. The Lake Tana region is a region in the north-western highlands of Ethiopia experiencing changes in the environmental balance forced partly by climate change, but mostly by the persistence of unsustainable production and consumption systems (Teshale et al, 2002). Lake Tana and its adjacent wetlands provide directly and indirectly a livelihood for more than 500,000 people (Gordon et al, 2007) and about three millions people live in the catchment.The pollution load into the lake has been made worse by the fast growing urban centres around the lake, especially Bahirdar City. The city found adjacent to the south extreme end of the lake harbours about 163,000 inhabitants (CSA 2006) and is currently expanding rapidly, with a lot of new construction taking place, including on the shore areas of the lake. The area of the city is Ca.29, 855 hectares (NUPI, 1996). It is a regional administrative capital and a commercial centre- drawing in migrants from the surrounding rural areas. Bahirdar has no centralized sewerage system and the majority of the population uses dry pit latrines. About a quarter of the total households have no other form of sanitary facilities and use open fields. There is no specific disposal site of the sewage and it is often disposed directly into agricultural land to be used as fertilizer. The existing factories discharge the effluent without any treatment. There is no organized site for solid waste disposal. The majority of the households in the town dispose garbage within the compound or into the open field and on the streets. Over 50% of the households dispose off on open fields while only approximately 39 % have a sort of garbage pit (WSSA, 2005). Waste from hotels, bars, restaurants and other commercial establishments is carried away by carts and disposed off in some other distant, but residential or commercial area. Sampling, laboratory and data analysis for determining input parameters for the wetland design : Water samples were collected from the sewerage line that joins Lake Tana near St. George using acid–washed 2 litre polyethylene bottles for chemical analysis and using autoclaved glass bottles with butyl rubber stoppers for microbial analysis based on standard procedures (APHA, 1995). In-situ measurements of electrical conductivity, pH, and total dissolved solids were made. pH was measured with coupled pH/mV/ Meter (Model CE 370 pH meter 01186, EU). Electrical conductivity and TDS were measured with Cond/TDS meter (Model CE 470 Cond Meter 01189).TSS was determined by gravimetric techniques (APHA, 1995). The procedure of SAK 254 / UV 254 determination was according to the manual on chemical water analysis by Matsche and Stumwohrer, (1996).Analyses of, ammonia; nitrite and nitrate samples were done immediately after collection with a mobile water analysis kit photometrically.
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Results Table 1 : Levels of faecal indicators (log CFU/100 ml) HPC (log CFU/1 ml) in Bahirdar gulf of Lake Tana. ND refers to non detectable (n = 22). TC: total coli forms, FC: faecalcoiforms, CP: Clostridium perfringens , HPC: heterotrophic plate count
Statistical tools TC FC E. coli CP HPC Maximum 6.3 6.2 6.1 4 4 Minimum 2.4 ND ND ND 1.1 Median 3.1 1.4 1.3 1.6 2.3 % Occurrence 100 86 82 90 100
Table 2 : Some physico-chemical characteristics of Lake Tana water, Bahirdar gulf area.Concentrations and standard errors of chemical parameters of pooled data (n = 22)
SAK NH 3 NO 2 NO 3 TDS TSS EC Statistical 254 nm (mgl -1) (mgl -l) (mgl -l ) (PPT) (mgl -l) pH (µS Cm -1) tools (m -1) Minimum 8.2 ND ND ND 0.04 1 6.8 130 Maximum 48.0 12 0.366 3.6 0.42 34 9.0 1200 Median 16.9 0.66 0.039 1.630 0.07 9.5 8.15 140 Mean 20 1.99 0.051 1.48 0.10 11.41 7.98 293 Std. Error 2.28 0.74 0.015 0.22 0.02 1.93 0.14 67.1 of Mean
Table 3 : Some physico- chemical characteristics of the wastewater (Aug. 2009) Temp. Cond. Statistical tool pH TDS n (0C) (µScm -1) Range 22-25 6.4 - 6.9 120 - 640 0.06 - 0.3 6
Table 4 : Input parameters used for the FWS-CW design Parameters Value Source Catchment runoff 0 Rousseau, 2006 Infiltration 0 Rousseau, 2006 Water depth 1.2 m Rousseau, 2006 o BOD 520 C 300 mg/l Original data TSS 30 mg/l Original data FC/TC 10 6CFU/100 ml Original data TO Coldest 17 Original data TN 41 Original data TP 1 mg/l Oroginal data Discharge(Q) 691 m 3/yr Yemenu,2005
Performance expectations (removal of contaminants) and design equations : Contaminants removal in this wetland (FWS) is described by a first–order model
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Ce = effluent number of FC (number / 100 ml) Ci = Influent number of FC (number/100 ml) C* = background number of FC (number/100 ml) q = hydraulic loading rate (m/year) Kt = first order temperature dependent removal rate (m/year)
O Kt is defined according to the temperature of the coldest month e in Bahirdar, which is 17 C and based on the value of K 20 given by Kadlec, 1997 as cited in Rousseau, 2006, also C* defined according to Kadlec, 1997 as cited in Rousseau, 2006.
Table 5: Parameter values for first order model of FWS constructed wetlands (Kadlec, 1997 in Rousseau, 2006) and measured input parameters values for first order model to compute q.
Parameters FC BOD TN TSS NH 4-N NO 3-N TP K20 (m/year) 75 34 22 3000 18 35 12 C* (mg/l) 300 3.5 + 0.05Ci 1.5 5+0.16Ci 0 0 0.02 C* (mg/l) 300 18.5 1.5 9.8 0 0 0.02 Θ 1.00 1 1.05 1 1.04 1.09 1
Table 6 : Summary of q, K 17 and proposed area for different contaminants computed based on first order linear model, A = Q/q
2 Parameters q (m/year) K17 (m/year) Area (m ) Pathogens (FC) 10.32 75 67.41 TN 12.36 19 56.27 TP 11.1 12 62.7 BOD 10.632 34 65.46
Area needed and aspect ratio of the wetland: Based on the previous information the horizontal area (m 2) of the wetland was determined using the quantity of WW coming into the wetland near ST. George (Ca. 696 m 3 per year) over the hydraulic loading rate for pathogens obtained by the first order model (See Table 6). Here we consider the average Q~Q because it does not vary significantly as follows:
The aspect of the wetland includes the dimensions (m) for the width and length, based on the recommendations of a ratio of 2:1(Wood et al ., 1995) in Rousseau (2006). A = L (m)*W (m), assume the ratio 2:1 2W 2= 67m 2 →→→ W = 5.8 m and L= 67/5.8 = 11.62m
Removal efficiency: Removal efficiency (RE) is computed as:
RE = (1 - )*100
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1.2m 11.62m 0.5m
Fig. : Model reporesenting sludge converion into environmentally friends form.
Table 7 : Removal efficiency of FWS-CW of the various contaminants computed based on the above formula
Parameters C in C out RE FC 106 10 3 99.9 TN 41 10 75.6 TP 1 0.1 90 BOD 300 30 90
Further considerations of the management plan include: • Process variables for loading rates of BOD, FC, TP, TN and TSS (Table 6), • hydraulic loading rate: The quantity of waste water that could be applied every day to the wetland was estimated using the following equation, where Q is equal to the amount of WW produced and A is the area of the wetland HLR = Q/A = 10.38m /year, and • Hydraulic retention time: The estimation of the needed residence or retention time of the water inside the wetland, was estimated using a relation between the depth and the hydraulic loading rate, we obtained a value of 42 days, so the water will stay in the wetland for 42 days in order to meet all the quality requirements before it is released to the lake. HRT = 1.2m/10.38m/year 0.11year = 42days.
Physical design factors Vegetation : The major benefit of plants is in transferring of oxygen to the root zone. Their physical presence in the system (the stalks, roots and rhizomes) penetrate the soil or the support medium, and transport oxygen deeper than it would naturally travel by diffusion. Perhaps most important in the FWS wetlands are the submerged portions of the leaves, stalks, and litter which serve as the substrate for attached microbial growth. It is the responses of this attached biota that is believed to be responsible for much of the treatment that occurs. The emergent macrophytes that can be potentially used for wastewater treatment in the shore areas of Lake Tana include Cyperus papyrus, Typha spp .etc Vector control in free water surface wetlands : FWS provide an ideal breeding environment for many insect pest species, particularly mosquitoes. However, biological control of mosquito larvae is possible and some studies have also reported that area coverage of FWS with duckweeds ( Lemna spp. ) is inversely related to mosquito density.
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Harvesting of vegetation : For free water systems, dry grasses are sometimes burned of annually to help maintain the hydraulic profile of the wetland and avoid build up of grassy-hillocks, which encourage channelization .An earlier harvest of plants prior to translocation of nutrients by the plant, or several harvests per season would be more effective for nutrient removal purposes. Harvesting may be desirable to reduce the excessive accumulation of litter that could shorten the life span of A FWS wetland. Operation and maintenance : Clogging, odor nuisance and the mosquito are some of the problems that coulde result from poor operation and maintenance of the FWS-CW. Daily monitoring and adjustment of flow, water levels, water quality and biological parameters plus less frequent repair of pumps, dikes and control structures, vegetation management, removal of solids and cover estimates and observations on plant growth are necessary. In addition to the above activities, measures like lowering loading rates, giving resting times for clogging; reducing oxygen demand (BOD, NH 4) by pretreatment for odor nuisance and temporary drying of the beds, lower water depths, open water areas, insecticides and biological control should be taken to solve the problems of mosquito larva.
Economics and reuse possibilities The major costs of FWS-CW are land acquisition, earth moving and liners in case of high hydraulic conductivity. The benefits-reuse possibilities are water reuse, nutrient harvesting, habitat value and human use including integrated wetland production. Unlike temperate areas, land is inexpensive and labor cost is also cheap in tropical areas. Nevertheless, it is assumed that land will be available from the municipality free of charge. The following running and investment costs are required.
Activity Unit Quantity Unit cost Total cost Excavation Man-days 600 50 30000 Planting Man-days 10 1000 1000 One person Months 12 300 3600 Technical person Man-days 20 100 2000 Compaction(red soil) m3 10 300 3000 Plastic tubes No. 30 100 3000 Concrete works No. 3 10000 30000 Contingency (5%) 3630 Total 75860 ** It is assumed that land will be acquired free of charge from BahirDar municipality in the shore areas of Bahirdar
Conclusion and recommendations The FWS-CW has more than 75 % expected performances for all parameters that need to be tested on ground. FWS-CW has wider implications regarding sustainable utilization and conservation of wetland resources of Ethiopia through assuring ecological roles. Implementation of the development plan before onset of rainy season is essential. Further work on the possibility of integrated wetland production should be sought. Environmental modeling works on optimizing removal efficiency of FWS – CW should follow application of this model.
References American Public Health Association (1995).Standard Methods for the Examination of Water and Wastewater, 19th ed. Washington: American Public Health Association, D.C. Birx, H., (1994). Functions of macrophytes in constricted wetlands. Water sci.Technol .35, 11-17 CSA. (2006). Central statistical authority of Ethiopia. National population and Housing Census.
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Gordon, A., Demissie, S.,Tadesse, M. (2007). Marketing systems for fish from Lake Tana, Ethiopia: opportunities for improved marketing and livelihoods. IPMS (Improving productivity and Market Success) of Ethiopian Farmers Project Working paper 2.ILRII (International Livestock Research Institute), Nairobi, Kenya.49pp. Matsche, N., Stumwohrer, K. (1996). UV absorption as control - parameter for biological treatment plants. Wat.Sci.Tech .33 , 211-218. NUPI. (1996). Bahirdar master plan final report (Executive summary).National urban planning Institute, Addis Ababa, Ethiopia. Polpraset.c, S. Veenstra and Ir.P.Vandersteen.(2001). Wastewater treatment II: Natural systems for waste water management. Asian Institute of Technology, AIT Bangkok-Thailand. IHE - Delft-The Netherlands. Shiny K.J., Remani K.N., Nirmala E., Jalaja T.K. and Sasidharan (2004).Biotreatment of waste water using aquatic invertebrates, Daphnia magna and Paramecium caudatum . Bioresource Technology 96:55.58 Shuiping C., Wolfgang G., Friedhelm K., Manfred T. (2001). Efficiency of constructed wetlands in decontamination of water polluted by heavy metals. Ecological Engineering 18:317–325 Rousseau, D. (2006). Wetland for water quality: Design of constructed wetlands for water treatment .Lecture notes.IHE DELFT-The Netherlands. Teshale, B., Lee, R., Zawdie. (2001). Development initiatives and challenges for sustainable resource management and livelihood in the Lake Tana region of Northern Ethiopia. Proceedings of the wetland awareness creation and activity identification workshop in the Amhara National Regional state. 23 rd January, Bahirdar. Amhara National Regional State, wetland action/ EWNRA: 33 – 45. Vymazal J.(2001 a). Types of constructed for waste water treatment: their potential for nutrient removal .In: Vymazal J.2005.Horizontal sub-surface flow and hybrid constructed wetlands systems for waste water treatment. Ecological engineering 25:478-490. Vymazal J.(2005).Horizontal sub-surface flow and hybrid constructed wetlands systems for waste water treatment. Ecological engineering 25:478-490. WSSA (2005). Towns’ water supply and sanitation study. Phase 1, Volume 3.Bahirdar.Water Supply and Sewerage Authority (WSSA), Ethiopia. Yemenu, A. (2005).Characterization of domestic wastewater disposal as point source pollution in southern gulf of Lake Tana, North-western Ethiopia. MSc thesis. Addis Ababa University, School of Graduate Studies. 88 pp. Yitaferu, B. (2007). Land Degradation and Options for Sustainable Land Management in the Lake Tana Basin (LTB), Amhara Region, Ethiopia. PhD thesis. Centre for Development and Environment (CDE).Geographisches Institut, Universitat Bern.
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Assessment of current fish status of Koga River and Dam, West Gojjam, Ethiopia
Miheret Endalew Tegegnie (M.Sc.): Amhara Regional Agricultural Research Institute, Bahir Dar Fish and Other Aquatic Life Research Center, P. O. Box 794, Bahir Dar, Ethiopia, [email protected]
ABSTRACT : Koga River is located at N 11.58 91° and E 37.37 97° and it is a tributary river to Gilgel Abaywhich nflows into Lake Tana that serves as spawning ground for the migrating Labeobarbus fish species. The pre-feasibility and feasibility study documents of the Koga River dam lack adequate fishery information during thes study and recommends it's requirementy in the future. Based on this gap statement, fish sample assessment was carried out for eight sampling periods (three samplings in 2006, four samplings in 2007 and one sampling in 2008) at four sampling sites starting from the confluence of Koga and Gilgel Abay Rivers upstream up to the Koga reservoir. The objectives of the survey was (1) to assess the current fish status of Koga River for one year through identifying the fish species composition, size, and abundance in the dry and wet seasons, (2) to characterize the fishery and assess impacts related to the reservoir construction upstream of the Koga River and propose measures to develop and sustain the fishery, (3) to create awareness among the different stakeholders through training workshops and /or other means of popularization as conditions permit. Gillnets of different mesh size for fish sample collection and other field equipment were used. The collected fish data and environmental parameters were analyzed. 279 individuals belonging to ten species, three genera and two families were identified from the four sampling sites, six species 106 (15%), two species 35 (5%), and 254 (37.74%) weren identified from Gilgel Abay and Koga confluence, Abay Gulit, Dengia ber and Koga dam, respectively. The highest species diversity was recorded from Gilgel Abay and Koga confluence followed by Abay Gulit sampling site and diversity decreased upstream towards the reservoir, whicht may be due to natural factors and upstream damming. The base flow immediately below the reservoir is highly reduced without considering the biodiversity requirement in general and the fish in particular. The local community subsistence fishing activity is open access without regulation and the open access resource use prevailing at present and uncoordinated water resources development activities will cause degradation of fish resources in particular and other natural resources in general. The different stakeholders involved in the development activities of Koga reservoir should be aware to develop, manage and sustain the Koga River and reservoir fishery and other living resources for the generations to come.
Key words : Diversity, fishery, Koga Reservoir, Koga River.
Introduction The Koga watershed (Fig. 1) with area coverage of 27,850 ha is situated between latitudes 11°10’ and 11°25’ north and elevation varying from 1890 to 3200 meters above sea level (Acres 1995). The Koga watershed falls in Woina Dega and Dega climatic zones with the majority being Woina Dega with distinct dry and wet season, the dry season between November and April and the wet season between May and October. Koga River is located at N 11.58 913° and E 37.37975° in Mecha Woreda, West Gojjam Zone in Amhara National Regional State. Koga River is one of the tributaries of Gilgel Abay that flows into Lake Tana and is used as spawning ground for the migrating Labeobarbus fish species. The upstream part of Koga River is under construction for dam that conserves the rainy season Koga river discharge for later irrigation to release during the dry season 3 (Fig. 2). The dam has 21.5 m height, 1860 m length, and a storage capacity of 77 Mm , with the spillway designed for a discharge of 336 m 3/s at a reservoir level of 2016.8 m. Further, the dam design was for provision of low-level outlet to release the dry season compensation with flow rate 1 m3 /s to the Koga River, irrigation off take 9.1 m 3/s, bottom outlet 31 m/s depending on the silt burden . There appears no designed structure of any fish path for upstream and down stream movement of fish. The Koga dam has a submergence area of 1700 ha comprising of Bojed plain, a wetland use per dry season grazing by the local community as well as outsiders, infrastructure to irrigate 7000 ha of command area with main and secondary canal network of length 16.7 km and 120 km, respectively. With this background the Bahir Dar Fishery and Other Aquatic Living Research Center planned to conduct the current fish status assessment at Koga River and the reservoir. The objectives of the Page | 24
Ma nagement of shallow water bodies ..., EFASA 2010 assessment were to identify the fish species, composition, size, abundance; characterize the fishery and assess impacts related to the reservoir construction upstream and create awareness among the different stakeholders to sustain and enhance the fishery resources in the Koga River basin.
Materials and methods Study Area : Koga River is located at N 11.58 913° and E 37.37975° in Mecha woreda West Gojjam Zone of the Amhara National Regional State. Koga River rises in the hills north of the Wezem Mountains and flows a distance of some 49 km to the point where it joins the Gilgel Abay that eventually discharges into Lake Tana. Gilgel Abay is considered as spawning ground for the migrating Labeobarbus fish species (Bahir Dar Fish and other Aquatic Life Research Centre). The upstream part of Koga River is under construction for reservoir. The reservoir would conserve the rainy season Koga river discharge for later irrigation release during the dry season. The fish status assessment was carried out at the confluence of Koga and Gilgel Abay Rivers (N 11.37 54, E 37.03 21), Abay Gulite (N 11.21 28, E 37. 04 32), Dengia Ber below the dam, with pools and rifles having >2 meters depth and confluence of Koga and Burka rivers (N 11. 20 31, E 37. 08 39) at the dam site. Data Collection and Analysis : Gillnets (6, 8, 10 andand 12 cm stretched mesh size) 25 m length and 2 m width were used and set for 12 hours during the night and lifted in the morning. ll of the fishes caught were identified to species level on site with the help of identification key (Nagelkerke et al., 1994). Measurements of fork length, total weight were taken using measuring board and sensitive balance. Each fish was sexed and dissected;. The gonad maturity stage of each fish was determined and recorded. Different field and laboratory equipment were used for the collection and analysis of different environmental parameters. GPS, Geographic Positioning System, (Garmin eTrex Venture TM personal navigator), oxygen meter, (Oxy guard International A/S (Denmark)), pH meter, (model 3050 ELE, electric Products (China)) and Conductivity meter (Hanna, Model H1 98312) were used for the measurement of environmental parameters. Water transparency was measured with Secchi Disk and measuring rope. Mecha Woreda Office of Agriculture and Rural development experts on livestock and extension were contacted and consulted for availability of fishery activity on Koga River. Libraries at the Regional Bureau of Water Resources Development, the Amhara Regional Agricultural Research Institute and Bahir Dar Fish and Other Aquatic Life Research Center were consulted for relevant literature.
Results Fish Species Diversity from Koga River and Koga Dam: A total of 674 fish specimens (Table 1 ) Male 293, Female 371 and 10 unidentified were collected. Ten species (Tables 2 and 3 ) belonging to three genera and two families were identified from the four sampling sites. Among the identified of ten species, eight species were Labeobarbus species (270 in number, 40.06 %) and two species were non-Labeobarbus species (404 in number, 59.94%). Wen the species, number and percentage is considered, (Table 4 and 5) ten species 279 (41.45 %) , six species 106 (15%), two species 35 (5%), 254 (37.74%) weren identified from Gilgel Abay and Koga confluence, Abay Gulit, Dengia ber and Koga dam, respectively. The most abundant Labeobarbus species include Labeobarbus intermidius , Labeobarbus nedgia , Labeobarbus crassibarbis and Labeobarbus brevisephalus, respectively. Clarias gariepinus and Varicorhinus besso species were caught together with the Labeobarbus species . Clarias gariepinus and V. beso were common in all the sampling sites. The highest number (223) of Clarias gariepinus was caught in the uppermost sampling site where Burka River was completely enclosed by the reservoir and Kurt Bahir was connected through Gibit River during wet season; these areas are well known sources for Clarias gariepinus . As expressed by the local people peak C. gariepinus migration occurs at the beginning of July when the Kurt Bahir and Koga flood plain are connected through the Gibit River. This movement may be related to spawning period for C. gariepinus . The
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Labeobarbus species was not found in the upper two sampling sites, namely, Dengia Ber immediately below dam site and Koga dam. The assessment work indicated that the diversity increased closest to the Gilgel Abay River which is considered as spawning ground for Labeobarbus species. It is reasonable to see higher diversity at sites that are closer to the spawning ground of Gilgel Abay even though the diversity may be dependent on the magnitude of sampling, the gear type applied in sampling and the time of sampling. The highest species diversity was recorded from Gilgel Abay and Koga confluence followed by Abay Gulit sampling site. As it is well known, a river system plays a vital role in the life cycle of migratory fish species. It is a route where spawners reach their spawning grounds, and fish in their young life history stages reach their feeding, shelter, refugee grounds. For such species, an obstruction like a Koga reservoir can spell fate. Koga reservoir not only prevents migration upstream, but also fish migrating downstream may not survive the effects of passage if led into irrigation ditches where they may be stranded and die. Under such situation fish death is unavoidable due to lack of fish passage structure and screening mechanism in the Koga dam construction design. Fish diversity decreased upstream towards to the Koga reservoir that may be due to natural and upstream damming-related factors. The base flow has been decreased from the reservoir downstream to Dengia Ber sampling site but the fish and biodiversity requirement were not taken into consideration. The environmental parameters (Table 6) did not show significant difference among the sampling sites conforming that the stated parameters are more or less similar but the base flow immediately below the reservoir is highly reduced without considering the biodiversity requirement in general and the fish in particular.
Discussion Fish species abundance in the Koga River and Koga dam : The most abundant species from all sampling sites was C. gariepinus constituting more than 45.25% and the abundance increased in the upstream, particularly very significantly at the Koga dam site. Labeobarbus species has 40.06 % composition and the abundance increased downstream towards the Abay and Koga confluence, and V. beso with 14. 69% composition was more or less evenly sampled in all sampling sites. The C. garipinus species is the most fished species and the local people are more dependent for their consumption and marketing at local level. The upper sampling site /dam site/ indicated also the number of C. gariepinus specimens was 223 (73.11%) when compared with the other three sampling sites. The number of Labeobarbus species increased downstream becausefor the reason that Labeobarbus species migrates in the Gilgel Abay River. Labeobarbus Intermidius is the most dominant species among the Labeobarbus species followed by Labeobarbus nedgia . Labeobarbus intermidius and Labeobarbus nedgia species collected in the Koga River were most probably dwelling in the river. This riverine- dwelling behavior of this species was also reported from Megech River basin (Wassie Anteneh, 2005) and in Ribb River (Abebe Getahun et. al, 2008), but this requires further research and verification. The current fishery resource status in the Koga River is not well studied and the inadequacy of the information on the fish resources has been stated in the pre-feasibility and feasibility study of Koga dam. The fish resource is in open access and the local community exploits it at subsistence level without adequate information of the fish resource and regulatory mechanism. The local people report a relatively high fishing activity during the wet season that may have direct relation to Labeobarbu s fish species migration, which remains to be confirmed in future. Presently the most frequently used fishing gears in Koga River and other nearby rivers and tributaries by the local communities are gill nets; scoop nets, traps, and hooks that are not controlled and managed. Illegal poisoning with Birbira (Milletia ferruginia ) is also used during the dry season when the river water flow level is at lowest level and poisoning with Birbira (Milletia ferruginia ) during dry season play significant role in devastation of the fish indiscriminately in the river course (pers. communication). Scoop nets are mainly used during the rainy season because gillnets are difficult to Page | 26
Ma nagement of shallow water bodies ..., EFASA 2010 set at flooding period where the river is at its maximum water level and with strong velocity. Traps, hooks, and scoop nets contribute little to the total catch in the local community fishing activities. The gill nets used by the local communities are either nylon monofilament gillnets (7 to 9 cm stretched mesh size, 20 to 30 m long) made locally by the fishers themselves and called traditional nets. Multi-filament nets (10 to 12 cm stretched mesh sizes, 50 m long) called modern nets are some times purchased at Bahir Dar (personal Communication). The traditional fishers use the above stated fishing gears in the Koga River mostly during the end of the wet season where flooding is minimized. The engagement of the local community in fishing on the river contributes in benefiting them for food security, getting cheap and good source of protein, economic and social aspects in job creation and income generation. The Bahir Dar Fish and Other Aquatic Life Research Center have also carried out preliminary fishing survey on Koga River at different sites Dam effect on fish and biodiversity : Dam building generally has a major impact on fish and biodiversity. These include among others: upstream and downstream migrations, accessibility of the quality and quantity of habitats, changes in water discharge, possible fish damage in irrigation canals, hydraulic turbines, over spillways and increased upstream and downstream predation, when fish are being delayed and concentrated due to the presence of the dam and, the habitat becoming more favorable to certain predatory species, including fishers. The negative effects of these obstructions have been much more significant than water pollution, over-fishing and habitat destruction in the main rivers preventing migration between feeding and breeding zones.
Conclusions and recommendations In spite of the large aquatic resources of social, ecological, genetic, environmental and economic values in the region, the research and development effort for conservation, development and management so far done is inadequate and uncoordinated. This situation may be due to inadequate attention by different stakeholders. Policy-makers, development actors, researchers, funding agencies, higher learning institutions and the public lack awareness of the nature of the aquatic systems and the resources they contain. As a result, there is virtually inadequate scientific information on the aquatic ecosystem and wetland resource base used by different stakeholders for different purposes. The unpracticed and fragmented aquatic ecosystem and wetland use policy in terms of conservation, management and development in an effective way on the available resource base is also a serious problem that requires adequate attention by the different stakeholders. If captured fishery and aquaculture are developed and sustained, the important contribution to food security and poverty reduction is enhanced. The aquatic ecosystems that support these resources need to be managed and maintained. In the face of growing pressure from diverse human interference on the aquatic resources as stated earlier, better information on the role of these ecosystems in sustaining capture fishery and developing aquaculture is required. Efficient use of this information in policy processes, development, management, researches and conservation at different levels may mitigate the existing situation .
Table 1 : Total sample of fish by sex
Sex Male Female Unidentified 293 371 10
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Fig. 1: Koga Watershed site Map (left). Fig. 2 : Koga dam under construction (right).
Table 2 : Species of fish identified from the different sampling sites of Koga River and Koga Dam.
Family Genus Species Cyprinidae Labeobarbus Acutirostris Cyprinidae Varicorhinus Besso Cyprinidae Labeobarbus Brevicephalus
Claridae Clarias Garipienus
Cyprinidae Labeobarbus Crassibarbis Cyprinidae Labeobarbus Gorguarir Cyprinidae Labeobarbus Intermedius Cyprinidae Labeobarbus Megastoma Cyprinidae Labeobarbus Nedgia Cyprinidae Labeobarbus Tsanensis
Table 3 : Occurrence and total number of species of fish from the different sampling sites of Koga River and Koga Dam
G. Abay and Koga Species Abay Gulit Dengia Ber Koga Dam Confluence Labeobarbus acutirostris Varicorhinus besso Labeobarbus brevicephalus Clarias garipienus Labeobarbus crassibarbis Labeobarbus gorguarir Labeobarbus intermedius Labeobarbus megastoma Labeobarbus nedgia Labeobarbus tsanensis
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Table 4 : Total abundance of species from all the sampling sites of Koga River and Koga Dam
Species Number Labeobarbus acutirostris 1 Varicorhinus besso 99 Labeobarbus brevicephalus 12 Clarias garipienus 305 Labeobarbus crassibarbis 13 Labeobarbus gorguarir 4 Labeobarbus intermedius 189 Labeobarbus megastoma 1 Labeobarbus nedgia 45 Labeobarbus tsanensis 3
Table 5 : Spatial distribution of fish in Koga Dam
Sampling Site No. Species Total number % G. Abay and Koga confluence 10 279 41.45 Abay Gulit 6 106 15 Dengia ber 2 35 5 Koga dam 2 254 37.74
Table 6 : Physico-chemical parameters of the sampling sites.
Temp.( 0C) Oxygen Sites pH Conductivity(uS/cm) (mg/l) G. Abay and Koga confluence 18.73 6.73 7.63 109.74 Abay Gulit 18.7 6.2 7.8 140.53 Dengia Ber 20.1 6.87 7.8 166.5 Koga Dam 20.14 6.95 7.63 190.7
Acknowledgements I am thankful to the BahirDar Fisheries and Other Living Aquatic Resources Research Center, the Amhara Regional Agricultural Research Institute, Amhara Region Bureau of Water Resources Development, West Gojjam Zone Administration, Mecha Woreda Agriculture and Rural Development Office. The Bahirdar Fisheries and Other Living Aquatic Resources Research Center researchers (Belay Abdissa, Goraw Goshu, Wondie Zelalem), technical assistants (Beniam Hailu, Birhan Mohamed) fishermen (Temesgen Minaye, Ayenew Gediff, Tiruneh Atanaw), and vehicle drivers, Asnake Aynekulu, Habtamu Muche and Habtamu Degu are acknowledged.. I am very hankful to Ato Mulat Workineh (at Abay and Koga confluence), Qeise Degu Worku (at Abay Gulit), and Ato Bekel Meles and Ato Genanew for their fishing service and guarding our nets during the night setting.
References Abebe Getahun, Eshete Dejen and Wassie Anteneh (2008). Fishery Studies of Ribb River, Lake Tana Basin, Ethiopia * Final Report VOL. 2, Presented to the World Bank-financed Ethiopian-Nile Irrigation and Drainage Project Coordination Office, Ministry of Water Resources
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Pre-feasibility study of the Birr and Koga Irrigation project, Koga Watershed and irrigation study main report Acres International Limited (Canada) in association with Shawel Consult International, Annex B Livestock, March 1995, (Ethiopia) Feasibility study of the Birr and Koga Irrigation project Koga Watershed and irrigation studies Acres International Limited (Canada) in association with Shawel Consult International Annex B Livestock, March 1995 (Ethiopia) Preliminary Fish survey on Koga River Amhara Region Agricultural Research Institute, Bahir Dar Fish and Other Aquatic Life Research Center November 2005, (Bahir Dar, Ethiopia) Preliminary Fish survey on Koga River, Amhara Region Agricultural Research Institute, Bahir Dar Fish and Other Aquatic Life Research Center, April 2006 (Bahir Dar, Ethiopia) Amhara Region Agricultural Research Institute, Bahir Dar Fish and Other Aquatic Life Research Center three years strategic plan (2004- 2006) Bahir Dar, Ethiopia. Amhara Region Agricultural Research Institute, Bahir Dar Fish and Other Aquatic Life Research Center internal reports (Bahir Dar, Ethiopia). Rural Development Policy and Strategy Federal Democratic Republic of Ethiopia Ministry of Information 2004, Ethiopia. Federal Democratic Republic of Ethiopia (2003) Fisheries Development and Utilization Proclamation No 315/2003 Federal Negarit Gazeta - 9th Year No 32 4th February of the Addis Ababa, pp. 2084 Wassie Anteneh, (2005) Spawning migration and Reproductive biology of labeobarbus (cyprinidae: teleostei) of Lake Tana to Dirma and Megech Rivers, Ethiopia. M.Sc.Thesis, Addis Ababa University, School of Graduate Studies
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National aquaculture development strategy of Ethiopia: A roadmap to building a healthy and dynamic aquaculture sub-sector
Hussein Abegaz Issa, P.O.Box 62347, Addis Ababa, Ethiopia
ABSTRACT: The National Aquaculture Development Strategy of Ethiopia (NADSE) has been prepared against a background of changing perspective on aquaculture region-wide. The Government of Ethiopia has taken a bold and multi-faceted approach to the national development process, with the central policy objectives focusing on the eradication of poverty, hand in hand with decentralization and macro-economic growth. This integrated approach has yielded a range of simultaneous policy initiatives that impact directly on the development of the agricultural sector and on the livelihoods of the rural poor. Despite this and the increased emphasis by government, the private sector, and development partners, aquaculture in Ethiopia remains generally underdeveloped. The country’s rich freshwater resource base with a potential to support a vibrant aquaculture industry remains untapped. The Rural Development Strategy (RDT) and “Plan for Accelerated and Sustained Development to End Poverty (PASDEP)” are the fundamental basis for aquaculture sub-sector strategy. In addition, there are other supportive policy documents and proclamation (Fish Resources Development and Utilization proclamation 315/2003), which will facilitate the development in aquaculture. This strategy provides a set of guidelines that stipulate roles and responsibilities for the various stakeholder groups, notably the public and private sectors as well as civil society. It is envisaged that this strategy will facilitate development of viable and sequential aquaculture plans. The strategy seeks to highlight the interrelationships between the public and private sectors and to help both the private and public sectors be more aware of their respective roles. It proposes, among others, means and methods of addressing critical issues relating to aquaculture development vis-à-vis input supply (i.e., production and delivery of feeds and seeds as well as the availability of farm credit) and access to extension support and markets. The strategy clearly delineates the specific roles and responsibilities of the private and public sectors. All these issues are addressed within the context of prevailing macro and micro-economic, social and cultural conditions involving a wide range of partners in the public and private sectors. In general, the strategy has provided the guidelines for the rational and sustainable development and expansion of the sub-sector. Implementing this strategy starts from creating awareness of it among all stakeholders .
Key words : Aquaculture strategy, Ethiopia, policy, gender issues.
Introduction The total annual fish production from rivers, small and large reservoirs was estimated to be 13,000 tones in 2007. The total annual production potential from different waterbodies is predicted in the range of 41,000 to 49,000 tones. It is reported that in some lakes, the production is rapidly declining while the demand for fish is increasing, especially in the big cities. The Federal Government of Ethiopia had initiated the Agricultural Development Led Industrialization, the Plan for Accelerated and Sustainable Development to End Poverty and the Sustainable Development and Poverty Reduction Programme. These developmental frameworks however do not provide a specific framework for the sustainable development of aquaculture in the country. They are not comprehensive and do not provide guidance to the development of aquaculture, neither at regional nor national level. In order to develop aquaculture sector of the country, developing clear strategy is the priority task. Its successful implementation, must take cognizance of the environmental and socio-economic conditions. The Ministry of Agriculture and Rural Development and the Food and Agriculture Organization of the United Nations / Sub-Regional Office for East Africa, took the initiative to prepare a National Aquaculture Development Strategy for Ethiopia . The state of the aquaculture industry: Culture based fisheries is a dominant type of aquaculture practice in Ethiopia. It involves stocking of newly constructed reservoirs with fingerlings collected from existing water bodies mainly with Tilapia. Semi industrial aquaculture practices are at an infant stage of development. This consists of extensive aquaculture operations in several small rural based
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Ma nagement of shallow water bodies ..., EFASA 2010 fishponds with sizes between 100-300m 2. Fish culture cages and pens have not begun yet. A national data on various aspects of aquaculture including total production is yet not available. Candidate species for aquaculture include Tilapias ( O. niloticus ) and the African catfish ( Clarias spp. ). Limited research activities are underway. The aquaculture capabilities of several other species present in the fresh water rivers and reservoirs are yet to be explored. Different types of institutions such as the Ministry of Agriculture and Rural Development and Environmental Protection Agency promote and regulate aquaculture development. Aquaculture is not part of existing irrigation, farming and water harvesting schemes in the country. A lot of work remains to be undertaken in promoting aquaculture. Few Universities and ATVET Colleges offer courses in aquaculture as a part of the fisheries graduate programme, but none offers aquaculture as a full graduate programme in their curricula to produce more skilled workers locally. Aquqculture development objectices: The overall objective of the strategy is to define a regulatory framework and to build a strong basis for the development of aquaculture in the country. The strategy seeks to integrate the aquaculture industry into the agricultural sector and to facilitate development of viable aquaculture plans. It also aims to provide a framework in which the aquaculture industry can be developed in an economically, socially and environmentally sustainable manner. Aquaculture development is to be targeted as an activity to ensure food security, alleviate poverty of rural farmers and to provide fish for domestic consumption and industry. Aquaculture development is to be planned, and executed as a business or commercial activity on a scale that contributes to profitability and is market oriented.
Definition of the strategic framework Identification of high potential aquaculture zones : A first step in determining where resources to develop aquaculture could be successfully used is the identification of potential areas. This screening should be supplemented with a comparison of existing aquaculture activities, including the concentration of existing producers and the presence of government and other infrastructures 1. Based on biophysical and socio-economic potential, aquaculture zones may well be subdivided into areas that correspond to input supply/delivery. For example, to the extent that private seed supply comes from specialized private hatcheries, these hatcheries will operate within areas circumscribed by the economic ability to deliver seed to producers. Definition of types of aquaculture : Commercial aquaculture can be defined as the farming of aquatic organisms, including fish, molluscs and crustaceans and aquatic plants with the goal of maximizing profits. Thus, the distinction between commercial and non-commercial aquaculture operations relies primarily on the existence or absence of a business orientation and on how factors of production such as labor will be paid. An aquaculture system is a combination of type of culture unit, level of intensity, culture species and scale or size of exploitation. Categorizing fish farmers and farms according to relative sizes, degree of capitalization and profit motivation is always difficult. In the aggregate, these categories are part of a spectrum that covers the full scope of production systems. If this spectrum reflects production intensity and investment level, individuals at the low end will likely internalize their aquaculture activities with little contribution to the public purse and little benefit from public services. Conversely, individuals at the high end of the scale may make important contributions to national aquaculture production but have relatively little need of public support. For the purposes of this strategy framework, producers have been divided into two categories: commercial and non-commercial. Commercial producers can be small medium or large-scale, and are active participants in the market. They purchase inputs (including capital and labour) and engage in off-farm sales of the fish produced. For these individuals, aquaculture is a principal economic activity. Non-commercial producers may also purchase inputs, mainly seed and feed, but rely chiefly on family labor and on-farm sales of the produce. An additional feature of non-commercial
1 Aguilar-Manjarrez, J. & S. S. Nath, 1998. A strategic reassessment of fish farming potential in Africa. CIFA Technical Paper 32. FAO, Rome. Page | 32
Ma nagement of shallow water bodies ..., EFASA 2010 aquaculture is the variety of enterprises comprising the farming system; i.e. undertaken to diversify production, improve resource use and reduce risks of such events as crop or market failure.
Formulation of the national aquaculture dvelopment strategy As a result of field visits to collect data, consultations with various interest groups and review of background reports and documents, the principal constraints of aquaculture development in Ethiopia were identified. The constraints could also be regarded as the principal issues, the critical success factors or the essential elements to be addressed in a sustained manner for a smooth take-off of the aquaculture industry in Ethiopia. The major amount of aquaculture production in the country at the moment is from the stocking and harvesting of reservoirs. Therefore, culture based fisheries was included in the analysis although not in its entirety. This analysis also applies to small-scale fish farming as well as to anticipated development of commercial aquaculture activities. The constraints identified relate to the following issues; availability and access to inputs, training, education, capacity building, extension/outreach services and research. Other critical constraints listed for redress concern fish health management, gender, access to land or aquaculture zones by enterprises, industries and fish farmers, legal and regulatory frame work, improved marketing of fish, public-private partnerships in aquaculture development, public awareness creation about the potentialities of aquaculture, policy issues, monitoring, control and evaluation of industry. The first draft NADSE report was produced after a series of meetings held by two TCDC consultants and a national Task Force of seven members set up by the Ministry of Agriculture and Rural Development (MoARD). The critical success factors or constraints were the first issues to be identified followed by the interventions required to address each of them to develop aquaculture in Ethiopia. At several follow-up meetings, the list of constraints and interventions were reviewed until a final list was agreed upon for the preparation of the draft strategy. A stakeholder consultative workshop was held to present and adopt the draft strategy. The stakeholders were selected to reflect the different interests involved in aquaculture management and development. Their views and recommendations were incorporated in updating the draft strategy. Government, represented through its ministries, departments and agencies, was identified as a major public stakeholder whose policies, activities and decisions are very crucial. All the other stakeholders were classified as private sector practitioners. The interventions required from each stakeholder have also been spelt out as part of the strategy. Key issues : A key factor for the successful implementation of the strategy is Government commitment at different levels. This will be manifested in the institution of vital measures such as the provision of tax incentives, formalizing public-private sector partnerships and roles, and in the implementation of the recommendations of the strategic framework. The government and the private sector should not play conflicting roles in hatchery and table fish production and in running fish farms. Any Government intervention should be for a very limited period at the beginning of strategy implementation. Government should limit its involvement in aquaculture development to monitoring, control and evaluation, and the creation of an enabling environment for the private sector to operate. The culture of ornamental species for export could also be an important source of revenue for the country. Introductions should be carefully considered to curtail any adverse consequences on the environment. Efforts should be intensified to increase fish consumption in the country so as to stimulate the growth of the aquaculture industry. The adoption of the following recommendations will also enhance the successful implementation of the strategy. • Establishment of the NADSE implementation committee. • Development of government-private partnerships in supplying services and inputs for the industry. • A review of the Investment Code and regulations to make it attractive to investors and financial institutions to pay special attention to aquaculture.
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• The setting up of intervention targets and benchmarks for the successful establishment and development of aquaculture in Ethiopia. • Avail necessary manpower and finance to implement the strategy. NADSE implementation committee : For rapid and successful implementation of the strategy, it is recommended that an implementation committee should be set up composed of different institutions. The following institutions have been proposed as members: • Ministry of Agriculture and Rural Development (2) • Ministry of Water Resources • The Environmental Protection Agency • National Regional Bureau of Agriculture and Rural Development (4) • The Institute of Biodiversity and Conservation • Ethiopian Agricultural Research Institute • Addis Ababa University • The Food and Agriculture Organization Sub Regional Office for Eastern Africa. It was also recommended that the MoARD directorate responsible for fisheries and aquaculture should appoint the chairperson for the committee. The secretary for the committee will be a fishery extension officer from the same directorate. It was strongly recommended that the committee implement the strategy and draw up an action plan immediately. It was further noted that private commercial operators be invited to join the committee whenever this was possible.
Elements of the strategic framework of and the role of the government and private sectors regrading the availability and access to Inputs
With regard to fish seeds government agents should: • Establish and strengthen model seed production centers till the private sector takes over. • Encourage commercial farmers and hatcheries to produce quality seed for the entire sub-sector. • Set up proper seed distribution centers and channels. • Support capacity building on seed production and distribution. • Maintain quality brood stock of selected culture organisms corresponding to the identified production systems. • Identify and select suitable candidate species for aquaculture. Private sector should: • Produce and distribute quality and traceable seed. • Maintain all data concerned with production, distribution and sales of fish seeds. • Adopt latest technologies on hatchery management and seed production.
With regard to fish feeds government agents should: • Develop guidelines on quality feed production and storage. • Facilitate the establishment of modern feed processing and formulating industry. • Educate private sector for the preparation of species specific fish feeds and their storage Private sector should: • Be aware of the Government strategy regarding different production systems within aquaculture zones. • Produce and distribute quality feed at affordable price to fish farmers. • Disseminate information on feed availability, quality, efficiency and price to the public sector. • Monitor feed performance, get feedback and keep records.
With regard to capital investments , government agents should: • Inform the lending institutions on the advantage and profitability of aquaculture.
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• Make information accessible on the other possibilities of financing. • Set up a developmental fund for aquaculture activities. • Evaluate the technical merits of investment proposals submitted to lending institutions for funding. • Advise fish farmers on where and how to access financial assistance. • Interact with the funding institutions to negotiate preferential interest rates for aquaculture development. • Encourage farmers to prepare feasible aquaculture business plans. The private sector should: • Build a capacity to organize business plans and management skills. • Develop strong and acceptable feasibility reports with all prerequisites for developing a business proposal. • Lending institutions should finance viable aquaculture businesses. Government and private lending institutions should: • Provide credit assistance for fish farmers based on quality proposals. • Monitor the disbursed funds through appropriate machinery. • Support farmers to establish savings and credit schemes to promote aquaculture business.
With regard to fishing gears and other aquaculture equipment government agents should: • Initiate and support the establishment of local fishing gear manufacturing factories. • Monitor fishing gear standards. • Educate farmers the use of nets while handling different stage of fish in fishponds. • Demonstrate the advantage and the use of other aquaculture equipments in fishponds. The private sector should: • Produce standard fishing gear materials and fishing gears. • Upgrade skill and knowledge of making and mending of fishing gears. • Demonstrate the operation and maintenance of gears and other aquaculture equipments for durability
To promote extension and outreach services , governmen agents should: • Establish and support national and regional aquaculture information networks in order to enhance outreach activities. • Provide technical assistance through an efficient aquaculture outreach programme. • Demonstrate and disseminate aquaculture technologies. • Train and equip aquaculture service providers. • Strengthen farmers training centers and associations to allow for ease of information delivery and sharing of best practices. • Facilitate communication channels amongst different aquaculture stakeholders. • Play a pivot role in outreach programs. • Maintain all activities and reports relating to out reach programs. • Facilitate farmer internships including farmer-to-farmer contact to enhance learning. Fishery and aquaculture professional organizations should: • Act as forum for information exchange among stakeholders. • Rationalize the marketing and purchasing of inputs, as well as to exert social control on service suppliers. • Defend the collective interests and lobby for appropriate intervention of the public sector. • Establish relations with the research institutions and other stakeholders. Private sector should:
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• Collect all baseline information for setting up out reach programs and inform the details to the government. • Obtain all appropriate extension material from concerned government agencies and other organizations involved in aquaculture. • Inform the government the constraints that they experience and solution sought.
In providing training, education and capacity building , government agents should: • Promote aquaculture education at all levels including the development of curricula. • Develop and support continuing training plans for aquaculture technicians, farm managers and researchers and assist in linking candidates with local, regional and international agencies providing training, education and distance learning options. • Allocate experts in a rational manner. • Provide appropriate hands on training to all existing fisheries personnel in aquaculture. The private sector should: • Provide feedback and advice on training, including the efficiency of training and required training needs. • Facilitate practical training opportunities on their farms.
In the case of research government agencies should: • Consider research on aquaculture as one of the priority areas in agricultural development. • Allocate adequate funds to aquaculture oriented research activities. • Identify gap area of research in aquaculture development. • Support applied and farmer-participatory research directed at different production systems. • Ensure that research is responsive to the needs of fish farmers. • Provide and support aquaculture research facilities. • Conduct research on aquaculture technology packages. • Upgrade status of research administration to a fully-fledged institute. • Demonstrate tested research outputs on aquaculture to users. • Patent aquaculture research innovations. • Develop infrastructure facilities for aquaculture research. The Private sector should: • Collaborate with government and establish modern facilities to conduct advanced research. • Adopt research results.
In refernebce to culture based fisheries practices government agencies should: • Ensure that conflicts arising out of the multi-purpose use and management of water bodies and water harvesting facilities are amicably resolved. • Co-manage the fisheries of water bodies with the participation of the private sector and fish farmers. The private sector should: • Actively participate in the conservation and management of water bodies. • Manage the fisheries, the water resource and other activities relating to their businesses having in mind the interest of all the other users. • Be aware of carrying capacity of the resource of sustainable development. • Protect water bodies from pollution/degradation while practicing cage farming in natural water bodies.
In reference to fish health management government agencies should: • Monitor and control fish health on fish farms and water bodies.
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• Educate fish farmers on fish health and fish health management. • Certify the quality and safety of fish imports and exports. • Make the surveillance of fish disease in natural and cultural systems. • Regular monitoring of water quality both in source water and in cultural systems. • Identify bacterial, protozoan and metazoan parasite infestations. • Find out other disorders in fish such as abnormality, nutritional disorders, pollution induced changes and other physiological disorders in cultivable fish. • Take appropriate prophylaxis and other curative measures. • Establish and strengthen Fish Health Laboratory in Ethiopia with international support. • Make provision for registry of fish cases from natural and culture systems. • Establish contacts with FAO and World Fish Center to develop and promote fish health programs. • Develop capacity for farmers to identify parasite and disease in its early stage of development in culture systems. • Train the farmers the methods of disease control in culture systems. • Develop quarantine methods to import seeds to assess their health. The private sector should: • Be responsible for the management, prevention and the control of the spread of diseases within and outside their farms. • Report outbreaks of diseases on their farms to the appropriate authorities. • Be familiar with the knowledge of water quality parameters • Be familiar with the common parasite and disease of cultivable fishers with their control.
With regard to gender issues government agenciesb should: • Promote gender equality and empower women on aquaculture. • Develop a strategy to incorporate more women in aquaculture practice, processing and marketing of aquaculture products. • Take into account the specific gender issues in the education, training and extension of aquaculture capability development programs. • Elaborate indicators of reference in the effective implementation of gender issues in the aquaculture sector. • Encourage community based aquaculture and village group concept to develop aquaculture with the involvement of women groups. • Develop capacity building for women group to undertake viable aquaculture methods. The private sector should: • Develop capacity building for women group to undertake viable aquaculture methods to ensure gender equality. • Know the details and provide on the involvement of men and women in aquaculture activities. • Know the funds allocated for addressing the gender issues.
In the case of access to land and aquaculture zones by industries and fish farmers government should: • Identify aquaculture potential areas. • Facilitate farmers and investors in suitable site selection for aquaculture. • Guarantee aquaculture investors' rights to land and their investment. • Develop technologies such as GIS and remote sensing for identifying and selecting suitable sites for aquaculture.
In the case of legal and regulatory framework government agencies should:
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• Establish clear and secure user rights to land and water for aquaculture investment. • Involve private sector and other stakeholders in policy and development of regulations. • Regulate quality and production of feed and seed. • Develop a system to ensure that all sectors are aware of the regulations. • Effectively implement the regulation. • Develop environmental protection rules and regulations for aquaculture activities. • Give legal backing to the collection, analysis and publication of reliable and up to date statistics. • Regulate the introduction of indigenous and exotics and the movement of aquaculture species. The private sector should: • Be aware of, adhere to relevant regulations, and control measures. • Follow procedures and regulations in the development of aquaculture practices. • Respect regulations on the introduction, importation and movement of aquaculture species. • Seek permit before establishing aquaculture farms. • Conduct environmental impact assessment for aquaculture enterprises. • Self regulate to ensure a safe-to-consume product is provided to all consumers. • Participate in the formulation of policies, strategies, regulations and development programs. • Provide complete and accurate data for monitoring by the Government.
In the case of improved marketing government agencies should: • Provide basic marketing infrastructure such as roads, electricity, potable water and communication facilities. • Provide information on fish wholesale and retail prices from main domestic markets. • Provide and make technical and economic information on preservation and other post-harvest processes, technologies and techniques available to producers and consumers. • Increase fish consumption by promoting new food fish recipes. • Develop marketing channels that are accessible to fish producers. • Protect local producers against unfair foreign competition provided that the protective measures conform to international agreements. • Promote marketing of fish by increasing clients’ acceptability of aquaculture products through fish quality assurance. • Assist fish farmers to increase incomes through value addition to their products.
With regard to public private partnerships government agencies should: • Assign clear roles to identifiable public and private institutions in the development of aquaculture. • Encourage private sector to produce inputs such as seed, feed and fishing gears. • Limit its involvement in aquaculture development to monitoring, evaluation and the creation of an enabling environment for the private sector to operate. • Government and the private sector should develop strong institutional arrangements in support of aquaculture development.
With regard to the public awareness reation government agencies should: • Promote aquaculture development by extending knowledge of the concept, skill and profitability of aquaculture to the public. The private sector should: • Promote aquaculture development by extending knowledge of the concept, skill and profitability of aquaculture to the public. • In the caes of monitoring, control and evaluation of the aquaculture industry government agencies should: Page | 38
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• Control the quality of aquaculture inputs (feed, seed, drugs, chemicals) and products through certification. • Enforce compliance with appropriate international codes such as the FAO Code of Conduct for Responsible Fisheries – CCRF. • Control introduction and export of aquatic organisms. • Establish a data collection, analysis and publication system for an effective evaluation of all aspects of the sector. • Ensure that Environmental Impact Assessment (EIA) studies are properly conducted before an aquaculture establishment is set up. The private sector should: • Comply with the regulations on the responsible conduct of aquaculture and on their obligations towards the conservation of the environment. • Obtain a permit before establishing an aquaculture establishment. • Regularly provide reliable and up to date statistics on their operations. • Comply with the quality standards set by Government for aquaculture inputs and products.
In the case of policy issues government agencies should: • Encourage the private sector to participate in aquaculture policy formulation. • Incorporate aquaculture production into the water harvesting, irrigation agriculture and hydroelectric power generation schemes. • Increase and sustain the contribution of aquaculture to food security and poverty alleviation. • Coordinate federal and regional state policies on issues related to aquaculture. • Promote aquaculture development in accordance with the New Partnership for African Development (NEPAD) Action Plan and the Millennium Development Goals (MDG). • Participate in the work of relevant international organizations such as the Food and Agriculture Organization (FAO), its Committee on Inland Fisheries and Aquaculture for Africa (CIFAA), the Aquaculture Network for Africa (ANAF) and the World Fish Centre. • Provide incentives for investors to undertake aquaculture business. • Put aquaculture to the rank of the priorities of government policy as stated in the PASDEP and RDS. • Encourage the integration of aquaculture with other farms.
Recommendations • Establish aquaculture strategy implementation committee. • Develop government-private partnerships in supplying services and inputs for the industry. • Undertake a thorough review of the Investment Code and regulations so as to make it attractive to investors and financial institutions to pay a special attention to aquaculture. • For a successful establishment and development of aquaculture in Ethiopia, intervention targets and benchmarks must be set. The priorities amongst them are the following: • Training and education for specialists in aquaculture such as researchers and extensionists. • Make a study to identify the suitability of the potential areas considered as good for aquaculture according to the different techniques. • Undertake sensitization programs to create awareness to different stakeholders in the country including the local people, communities, investors, NGOs and donors. • Formulate aquaculture technical packages fitted to the various physical, social, environmental, cultural and socio-economical concerns. • Undertake pilot projects in agro-ecological zones which have the best potential in aquaculture.
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The aquaculture boom in west Shoa Zone, Oromia, Ethiopia
Daba Tugie, Zeway Fisheries Resources Research Center P. O. Box 229, Zeway, Ethiopia
ABSTRACT: Fish production provides high quality and cheap animal protein, which is often irreplaceable and crucial to the balance of diets in marginally food secure communities. Aquaculture has grown rapidly and is considered as the fastest growing of food production sector all over the world due to capture fisheries resources being depleted by destruction and fragmentation of aquatic habitats. Attention has been given to develop and expand fish culture in west Shoa Zone where, before two years, fish farm tradition was non- existent. From June 1/2009-21/2009 assessment of potential aquaculture ponds, sites and evaluation of community perceptions towards aquaculture development was conducted in eight districts. In addition, identification of fish specieswhich occurred naturallyor were introduced was carried out. During survey was conducted in 28 fish ponds which were different in size and found in various conditions. Out of these ponds, nine were stocked with Nile tilapia and Tilapia zilli fingerlings and fifteen ponds were ready for stocking after minor modifications while the rest four ponds were found not properly prepared. At the end of the surve,y including the modified fifteen ponds, within two years from February 2008 to the end of June 2009, twenty four ponds with a surface area of 4,538m 2 were stocked with 9,655 Nile tilapia and Tilapia zilli fingerlings. Regardingo pond water physical parameters, the temperature and transparency (secchi disk depth) ranged from 18 to 24 oC and from 21 to 56.5cm, respectively. To assess the general conditions and evaluate community perception on aquaculture development in the area, PRA was conducted among 32 respondents. Thee PRA survey result revealed the positive community perceptions of fish farm and utilizing, readiness to buy and consume fish, requirement of technical, material and financial assistances which were supported by 71.87%, 100%, 53.12%, 21.87 and 34.37% ,respectively, of the respondents..
Key word/phrases : Aquaculture, fingerlings, Nile tilapia, participatory rural appraisal, perception, Tilapia zilli . . Introduction Aquaculture is the rearing/farming of fish and other aquatic organisms. It has grown rapidly and is the fastest growing food production sector in the world. Aquaculture contributes significantly to ensure food security at household level, poverty reduction, create job opportunity, alternative income, food source and benefits the livelihoods of the rural communities (Edwards, 1999). Aquaculture enhances fish production, maximizess social well-being and can be an integral/diversification component of development. It is also plays an important role in global efforts to eliminate hunger and malnutrition by supplying fish and other aquatic products rich in protein, essential amino acids, vitamins and minerals (Subasighe, et. al., 2009). Fish farm can be a viable enterprise for a region where economic and food security goals can be achieved at reasonable costs. It is obvious that the region as well as the country is under animal protein deficiency in the diet and some areas are famine- affected. To tackle the problem of balanced diet, developing fish farm/culture is substantial, and this could support capture fishery and enable producing animal protein in alternative ways. The gap between supply and demand of food fish has been widening rapidly due to the decline of capture fisheries production and a continually growing population of the world. It is apparent that aquaculture in Ethiopia remains more potential than actual practice or is non-existent, despite the fact that the country’s physical and socio-economic conditions support its development (FAO 2003: Brook Lemma 2008). Assessment of potential aquaculture ponds and sites was conducted from June 1/2009- 21/2009 in west Shoa zone, Oromia Regional State. This area was where either capture fishery or aquaculture activities were not practiced or existant two years ago. The survey was conducted on 28 fish ponds in eight districts by tateam organized by Oromia Livestock Development, Health and Market Agency Bureau (Bulbula Regassa) and included Zeway Fisheries Resources Research Center (Daba Tugie) and West Shoa Livestock Development, Health and Market Agency office (Negew Lama). The observed ponds had different surface area and varied conditions. During the survey period, ponds
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Ma nagement of shallow water bodies ..., EFASA 2010 which were stocked with O. niloticus and Tilapia zilli were observed. For the first time, farmer’s fish ponds were constructed in 2007 through the assistance of DA in the area, and stocked with Nile tilapia and Tilapia zilli fingerlings in February 2008 by Sebeta Fishery Research Center (especially by Yared Tigabu and Fasil Degefu). To assess the general conditions and community perception in the area, Participatory Rural Appraisal (PRA) was conducted with 32 respondents who were selected purposefully. The aim of the survey was to assess potential aquaculture ponds and site and identify fish species naturally found or stocked, appropriate for pond culture system in west Shoa zone.
Materials and methods Study area description: Oromia Regional State
West Shoa zone
Fig. 1 : Map showing sampling area
According to West Shoa Livestock Development, Health and Marketing Agency Work Plan (2001/2002), west Shoa zone is one of the productive zone of the regional state located at the border of capital city Addis Ababa by the western side. The surface area of the zone is 14,921.19Km 2 and it has 18 districts with a population of 2,080,698. Regarding to agro-ecology of the zone 27% is highland (Daga), 56% is mid highland (Weyinadega) and 17% is lowland (Kola). It lies atan altitude ranging from 501 to 3,500m.a.s.l. and the average minimum and maximum temperature was 10-15 and 20-25C o, respectively . Average annual rainfall ranged from 812-1,699 mm. The estimated livestock population were cattle 1,767,482; goat and sheep 1,552,237, equines 320,953; poultry 950,021 and beehives 143,250.
The survey was divided in two phases: First phase: • Visual observation on the topography of the land/area of the pond site. • Visual observation and collection of information from respected bodies, on pond location, purpose of construction, water source, type, shape, depth, area, inlet and outlet, overflow, wall, soil type and year of impoundment. • Measuring pond water temperature using thermometer, water transparency using secchii disk and elevation/altitude using altimeter. • To evaluate community perception, Participatory Rural Appraisal (PRA) was conducted with 32 respondents which weree purposefully selected and requested to reply various questions and the replies were recorded on prepared questionnaires. The community perception evaluations were Page | 41
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about fish culture/ aquaculture development, awareness creation, ccustom of people in utilizing fish, fish market(supply and demand), impact of fish pond, required assistance from respected institutions and major constraints that hindered constructing fish ponds. • Discussion on fish culture issues with pond owners, development agents and Woreda Livestock Development, Health and Marketing officers was carried out. • After detail discussions, we reached on an agreement with pond owners whose ponds needed minor modifications (inlet and outlet, overflow, walls and shape) and if ponds were modified soon, owners were promised to havem stocked within a short time. • During assessment, six ponds which were stocked with O. niloticus and Tilapia zilli by Sebeta Fishery Research Center and three ponds with fingerlings by fish farmers who receivedawareness training from Sebeta staff were observed. Second phase: • According to the agreement with fish farmers and LDHMA staff in the second phase, after two weeks, 15 modified ponds werestocked with O.niloticus and Tilapia zilli fingerlings which were collected from Lake BaboGaya, Bishoftu. • Gave guidance as training on the ponds’ site to fish farmers, on general pond management (routine work, controlling of water exchange, inlet and outlet, clearing and cleaning, overflow and fertilizing), feeding time and type, health issue, predators' control.
Results During the first phase of the survey, the team identified 28 potential ponds in eight districts which were at diferent conditions. 9 ponds were already stocked, 15 needed minor modifications such as water inlet and outlet, overflow, walls, shape and the other 4 ponds were found with major problems(design, site, water source, surface area, shape, place and slope) (Table 1). In two districts, six fish ponds were stocked with 6,100 O. niloticus and Tilapia zilli by Sebeta Fishery Research Center from February 2008 while three ponds were stocked with 300 O .niloticus and Tilapia zilli by fish farmers by purchasing fingerlings from their neighbors (Table-2). Fifteen ponds were located in three districts which were modified during the first phase and stocked in the second phase with 3,255 O.niloticus and Tilapia zilli fingerlings by the organized team (Oromia Livestock Development, Health and Marketing Agency Bureau, Zeway Fisheries Resources Research Center and West Shoa zone Livestock Development, Health and Marketing Agency office) after mid June 2009(Table 3). In total, from February 2008 to the end of June 2009, twenty four ponds with a surface area of 4,538m 2 were stocked with 9,655 Nile tilapia and Tilapia zilli fingerlings in the area. During the survey period, some physical parameters, such as water sources, altitude, atmospheric and water temperature, transparency/secchii disc depth, availability of animal manure to fertilize ponds and potential agricultural products for fish feed were collected(Table 1 and 4). In addition, PRA was conducted to evaluate community perception on aquaculture development in the area. To evaluate community perception on aquaculture development, PRA was conducted as part of survey in the area. 32 respondents (Table 4) were purposfully selected based on the ownership of the ponds and neighborhood. To evaluate rapid future sustainable development of aquaculture in the area, the PRA survey result revealed positive community perceptions of fish farm and utilization (71.87%). 88.23% of respondents were positive on future fish market and demand which could encourage fish farms, promotion of aquaculture development and enhanced fish production, and readiness to buy and consume food fish. In addition to the above community awareness indicators, respondents emphasized the need for technical, material and financial assistance. These major and decisive points and other analyzed facts which are described in Table 4 have enabled us to judge/to be confident on the sustainable future aquaculture development in west Shoa zone.
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Table 1 : Number of assessed ponds and their physical descriptions in the first phase ( O.n. for Oreochromis niloticus and T.z. for Tilapia zillii .
) ) 2 Farmers Name of Temp. 0C Pond
(m)
No. name District fish problem period period species m.a.s.l. Year of Distanc (month) Altitude Altitude
Stocking (Conditions) town (km) Sechii discSechii depth (cm)depth Pond depth Stocked fish from nearest water source Area in (m Impoundment No. of Stocked Air Water 1 Brehanu Ambo 4- 100 02/2009 O.n. 400 3/2009 Huluka 1.0 2100 25.0 30 21 Bayesa Ambo river 2 Tesfaye Ambo 8- 100 - - - - Taltale 2280 - - major Derersa Ambo river modification 3 Tekel/M Toke 1- 100 04/2009 - - - Endres 1.65 2000 minor Asfawu Kutaye Gudar river modification 4 Ayala Toke 1- 24 03/2009 - - - Chole 0.85 1980 56.5 28 20 minor Haile/M kutaye Gudar river modification 5 Organiz Ginde- 16 04/2009 - - - Develope 1.0 2270 - - major youth21 Beret d well modification 6 D. Agent Gend- 4 02/2009 - - - public 0.50 2380 24 22 major demonstr Beret water modification 7 Tolosa Genda- 16 03/2009 - - - 2380 major Beka Beret modification 8 Dagafa IluGalan 5-Ejaje 1600 05/2007 O.n.; 4500 2/2008 Etesa 1.30 1800 26.0 24 22 Bekele T.z. borehole 9 Lema ,, 4-Ejaje 150 10/2008 O.n.; 300 12/209 Alanga R. 1.25 1840 20 18 Itafa T.z. 10 Daraje Dano 117 04/2009 - - Borehole 0.60 1630 17.5 30 24 minor Alemu modification 11 Takele Dano 450 03/2009 - - Burkitu 1.50 1690 55.0 30 24 minor Dinsa Laku R. modification 25 ,, - - - ,, 1.50 1690 30 24 ‘’ 1.5- road 16 ,, - - - ,, 1.50 1690 25.0 30 24 ‘’
84 ,, - - - ,, 1.50 1690 30 24 ‘’
12 ‘’ - - - ‘’ 1.10 1690 25/0 30 24 ‘’ 12 Nagasa Dano 32 ,, - - - Boso river 1.50 1780 minor Kabtyimar modification 13 Mamo Bako- 17- 130 04/2009 - - - Sama 1.50 1640 22.0 24 22 minor Page | 43
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) ) 2 Farmers Name of Temp. 0C Pond
(m)
No. name District fish problem period period species m.a.s.l. Year of Distanc (month) Altitude Altitude
Stocking (Conditions) town (km) Sechii discSechii depth (cm)depth Pond depth Stocked fish water source from nearest Area in (m Impoundment No. of Stocked Air Water Chala Tibie Bako river modification 14 Kasa Bako- 500 02/2009 - - - Borehole 1.50 1660 26.5 28 23 minor Fantahun Tibie modification and 2-Bako 320 ‘’ - ‘’ 1.50 1660 28 23 ‘’ Yesuf 200 ‘’ - ‘’ 1.50 1660 24.0 28 23 ‘’ Hasan 10 ‘’ - - ‘’ 1.50 1660 22.0 28 23 ‘’ 10 ‘’ - - ‘’ 1.50 1660 23.0 28 23 ‘’ 15 Aguma IluGalan 5- Ejaj 264 11/2008 O.n.; 300 12/08 river 1740 Shuguti T.z. 16 Abebe IluGalan 5- Ejaj 66 11/2008 O.n.; 300 12/08 river Senbeta T.z. 17 Motuma IluGalan 1.3- 55 11/2008 O.n.; 300 12/08 river Regassa Ejaje T.z. 18 Bakele IluGalan 3- 105 11/2008 O.n.; 100 12/08 river Gemechu Ejaje T.z. 105 11/2008 100 12/08 river 45 11/2008 ,, 100 12/08 river
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Table 2 : The stocked ponds observed during the survey
No. Name of district Peasant association No. of stocked ponds 1 Ambo AwaroKora 1 Saden Ilu, JatoDerke, GobaWalshomo, 2 Ilu-Galan 8 Ergo-Walshamo Total number of ponds 9
Table 3 : Stocked/introduced ponds in the second phase after minor modifications of ponds in the third week of June 2009 with Nile tilapia and Tilapia zilli fingerlings. (Notes: Stocked Tilapia zillii were less in number than Nile tilapia .)
No. of Name of Peasant Owner of the No. of Area Stocked No. stocked district association pond ponds (m 2) fish fingerlings species Emala Dawe Teklemariam; Nile Toke 1 Ajo and Ayala 2 124 248 tilapia Kutaye Nagafile Tilapia zillii Dire Dano, Daraje; Takala; Nile 2 Dano Dano Roge Nagasa 7 724 1448 tilapia Tilapia zillii OdaHaro and Mamo; Kasa; Nile 3 BakoTibie Danbe Gobu Yesuf 6 1,180 2360 tilapia Tilapia zillii
Table 4 : Ranking of evaluation of community perception and need assessment of respondents (pond owners 15 and others 17; total 32)
Assistances needed in(%) Material (fishing net, No. Description feed, balance, Yes (%) No (%) Suitable land and water source Technical (training, advice, etc. container) Financial problem 1 Level of awareness /knowledge 12.5 87.5 on aquaculture in the area before two years 2 Tasting food prepared from fish 67.75 25 3 Fishing practice//trades 4 Good knowledge before fish 0 100 pond established on how it is 0 100 hard, labor and capital intensive 5 Interest to have own fish pond? Interest to eat, buy and use 46.87 6.25 fish 6 Availability of surplus grain 88.23 11.76 production for fish feed and Page | 45
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Assistances needed in(%) Material (fishing net, No. Description feed, balance, Yes (%) No (%) Suitable land and water source Technical (training, advice, etc. container) Financial problem animal manure to fertilize your 62.5 37.5 pond? 7 Malaria prevalence in this particular area 8 Negative impact of established 75 25 pond • Ecologically • Economically • Socially - - 9 Community perception on 18.75 81.25 aquaculture - - • Positive • Negative 71.87 • No idea 10 Presence of predators (birds 6.25 and other vertebrates) 21.88 11 Cultural practices in the area to utilize fish 81.25 18.75 12 Are people accustomed to use fish 17.65 82.35 13 Access of fish market in the area 17.65 82.35 14 Fish demand in the area 15 What type of assistances 37.5 62.5 40.62 53.12 21.87 34.37 needed 17 What are the existing 53.12 46.87 76.47 41.18 23.53 constraints hindering to have fish pond?
Recommendations 1. Ponds should be properly designed, Planned andand constructed in the appropriate site to commercialize the fish farm and even for home consumption, and well prepared and modified ponds should be stocked soon with desired species (O.niloticus ). For the future based on agro- ecological condition and consumers preference eg. (O.niloticus or Syprinus carpio or Clarias gariepinus and etc. 2. Ponds which are not properly designed, not easily modified and are at inappropriate sites should be redesigned, reconstructed and stocked by desired fish species mentioned above, considering the agro-ecology of the area. 3. Establish moderrn indoor or outdoor hatchery to produce fish fingerlings/seeds at farmers level to supply fish farmers seed in the suitable sites at reasonable prices. To establish such hatcheries, governmental/NGOs continuous support is imperative. 4. Fish feed/pellet producing plant or simple factory is crucial for fish culture development. 5. Technical support should be given, such as training, advice, follow up for fish farmers and LDHMA staff e.g. on pond construction, management, feeding, fishing gear making and mainding, harvesting and post-harvest. For fish farmers families, fish traders and hotel owners on post-harvest (handling, processing and preservation), and preparation of different food type from fish. Page | 46
Ma nagement of shallow water bodies ..., EFASA 2010
6. Material support (e.g., nets, seed, packing materials, etc.) should be given to fish farmers at the earliest stage to encourage andand strengthen them. 7. Continuously serious attention should be given to promote aquaculture development to ensure food security, creating job opportunity, generate alternative income. 8. Assign responsible fishery experts at zonal and woreda level, who will work with allocated budget and means of transportation for fry/fingerlings as well as for woreda LDHMA. 9. Seek a controlling system/solution for excessive breeding or over population of O. niloticus at fish farm level
Acknowledgements I am very grateful to Sebeta Fishery Research Center, especially Yared Tigabu and Fasil Degefu for their valuable andand unforgetable effort to establish aquaculture in west Shoa zone. I would like to express my deepest gratitude to Oromia Livestock Development, Health and Marketing Agency, especially Ato Bulbula Ragassa for his unlimited effort (leading the organized team, direct participation in survey and stocking) and west Shoa Livestock Development, Health and Marketing Agency, especially Ato Negewo Almu and Wored experts. My gratitude is to Ambo Agricultural University, especially Ato Alemayehu Negassa and Prof.Natarajan for their great and valuable effort to train and support fish farmers. Also I wish to thank Zeway Fisheries Resources Research Center and Aschalew Lakew from Sebeta for his effort to train fish farmers and others who were involved to develop and expand aquaculture.
References Brook Lemma (2008): Introduction to Lake Ecology, Aquaculture and Fisheries in Ethiopia . Haramaya University, Haramaya, Addis Ababa University Press, Addis Ababa, Ethiopia. pp 416 Chakroff M. (1977). Freshwater Fish Pond Culture and Management .USA, Wadshington, DC. CTA (1996). Small-scale freshwater fish farming. Edwards P. (1999). Aquaculture and Poverty: Past, Present and Future Prospects of Impact. Bankok, Thailand. Edwards P. (2000). Aquaculture, Poverty Impacts and Livelihoods . FAO (1996). The State of World Fisheries and Aquaculture. FAO, Rome. FAO (1999).Aquaculture Newsletter. FAO Fisheries Department, Rome. FAO (2003). The Federal Democratic Republic of Ethiopia General Economic Data. James H. et.al., (2001). Fish as food: aquaculture’s contribution. EMBO reports. Subasighe R. et. al., (2009). Global aquaculture and its role in sustainable development.Aquaculture Management and Conservation Service, Fisheries and Aquaculture Department, Food and Agriculture Organization of the United Nation, Rome, Italy. LDHMA (2001/2002). West Shoa Livestock Development, Health and Marketing Agency Work Plan. Ziad, H. et.al ., (1996). Aquaculture Newsletters. FAO Fisheries circular, Rome.
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The effect of stocking density and supplementary feed on growth performance of Nile tilapia [( Oreochromis niloticus (Linneaus, 1758)] in cage culture system in Lake Elen, Ethiopia
Abebe Tadesse, Debre Birhan University, Biology Department, PO. Box 269, Ethiopia, [email protected] Abebe Getahun, and Seyoum Mengistou, Addis Ababa University, Biology Department, Addis Ababa, Ethiopia
ABSTRACT : A combined-sex juveniles of 30 ± 0.49 g (mean + SE ) weight were stocked in five treatments with stocking densities of 50/ m 3 (Ta), 100 / m 3 (Tb), 150 / m 3 (Tc), 200 / m 3 (Td) with supplementary feed, and 100 / m 3 (Te) fish without supplementary feed. All treatments were in duplicates. The fish were fed 5% of their body weight per day for 87 days using a demand feeder. Individual fish held in cages with lower density were heavier than the ones held at higher densities and had higher weight gain and daily weight gain. In terms of growth parameters, the most effective stocking density was 100 fish/m 3that reached 136.31 g of body weight per fish. Feed conversion and condition of fish were also affected by stocking density and supplementary feed. Tilapia growth in feeding treatments was significantly better than the control treatment (Te). Feed conversion ratio was negatively affected by stocking density with significant difference (P < 0.05) between cages. Fulton condition factor was negatively affected by stocking density and positively by supplementary feeding. Stocking density and supplementary feed did not affect survival rate (P > 0.05). Gross yield increased with increasing stocking density and addition of supplementary feeding in all cages (P<0.05). It is concluded that Nile tilapia can be cultured in cages at 100 fish/m 3 and gives good yield with supplementary feeding. This system can be used to improve food production for nutritional security and promote food alleviation in developing countries such as Ethiopia.
Key words/phrases : Cage, Ethiopia, Growth rate, Lake Elen, Oreochromis niloticus , Stocking density.
Introduction Ethiopia has rich water resources. Wood and Talling (1988) stated that the country contains 7,400 km 2 of standing water and 7,000 km length of rivers. The country has recorded about 153 indigenous and 10 exotic fish species, even if an exhaustive survey of the Ethiopian fish has not been carried out (Abebe Getahun, 2003). Until recently, Ethiopia had a solid fish potential estimated at over 51,000 tons (MOA, 2001). Despite substantial water resources and crucial need for food supply, fish production is much lower than the potential (Breuil, 1995). Moreover, over the last few years, there has been a huge increase in fishing effort and production in some fresh waters. For instance, Lake Chamo has seen a dramatic increase in landings (a 220% increase from 3,200 to 10,400 tons). In Lake Hawassa, the number of fishermen increased by 25% and the number of gill nets increased by 55% (LFDP, 1996) in 1992 and 1993. Since a lot of fisheries data remains unrecorded, it is likely that these figures underestimate the real increase in effort and production. It has moreover been documented that as a result of the increase in fishing effort and production, many fish stocks have already started showing signs of over-fishing (LFDP, 1997). For instance, between 1994 and 1995/1996 the contribution of Nile perch to the total landings dropped from around 70% to 10% (from 190 tons to 20 tons per month) in Lake Chamo, while the landing from Lake Hawassa dropped by nearly 50% (from 910 tons to 500 tons per year) during 1994- 1996. Therefore, if current trends of fishing activities go on for some time, it will not take long for some of the country’s fish stocks to collapse. In Ethiopia, fish consumption is increasing and demand is also increasing but all the supply is provided by natural catch from the country's lakes and rivers. With the supply threatened by overexploitation, developing alternatives such as fish farming, or aquaculture, becomes crucial. Aquaculture has been receiving considerable attention in recent years in many parts of the world as a means of increasing fish supply as well as reducing the pressure exerted on capture fisheries (Boyd et al ., 1979). However, aquaculture in Ethiopia is still in its initial stage, despite favorable physical, chemical and biological conditions. The high central plateau above 2,500 m, which represents 11% of the total area of Ethiopia, could be appropriate for all year-round farming of cold-water species. The surrounding central highlands present temperature characteristics favorable to production of a large number of cold water and warm Page | 48
Ma nagement of shallow water bodies ..., EFASA 2010 water fish species (Tekalign Mamo et al ., 1993). The lowlands (33% of the total area) offer ideal temperature conditions for warm water species, but are unfortunately water deficit zones. In such localities, water storage macro and micro-dams could, however, be employed for fish production. So, these areas are open for aquaculture installation (Breuil, 1995). Considering the opportunities available for aquaculture, it is surprising that no such activity has been undertaken by the government or fisher folk. The lack of research input has been another problem to promote aquaculture in the country. Therefore this study is one such effort to investigate the potential of cage culture in one lake, and to see the effects of stocking density and supplementary feeding on growth performance and yield of tilapia. Nile tilapia (Oreochromis niloticus L.) is one of the most suitable species for aquaculture. Nile tilapia is cultured primary in the semi-intensive ponds based on fertilizers or on integrated systems with livestock (Edwards, 1986; 1991). There are very few previous studies on cage culture of tilapia in Ethiopia (e.g. Ashagre Gibtan et al ., 2008). Nile tilapia, which is considered an “every man’s fish” was also considered as the culture fish in this study. This is due to its ability to efficiently use natural foods, being herbivore in nature and of short food chain, resistant to disease and handling, tolerant to wide range of environmental conditions and schooling behavior. To enhance fish growth and yield in cage culture, control of size and production are two important tasks to meet the market demands. In addition, increasing the stocking density is a way of dealing with problems of land shortage and increasing fish intensification (Omar, 2006). Increasing production of market size fish with increasing stocking density is one alternative (Beveridge and Haylor, 1998). Papst et al . (1992) suggested that in intensive aquaculture, the stocking density is an important factor that determines the economic viability of the production system. According to Coche (1982), the minimum stocking fish number recommended for tilapia culture is 80 fish/m 3 and the maximum stocking density is the number of fish that will collectively weigh 150 kg/m 3 when the fish reach a predetermined harvest size. In this study, we had to decide on the stocking densities and supplementary feeds to be used for cage culture of tilapia based on literature and experience of the BOMOSA trials in East Africa The aim of this study was to determine the optimal stocking density and the best growth performance and yield of tilapia under different stocking and feeding conditions. The result from this study could be used for promotion and adoption of simple cage culture system to be used by poor fishers and farmers in Ethiopia, as a complimentary way to enhance food security in the country. The specific objectives were to: • assess effect of stocking density on growth performance and survival rate of O. niloticus in cages; • compare the differences in growth performance of O. niloticus on natural foods and supplementary feed in cages; • evaluate the final yield of tilapia at different stocking densities; • assess the effect of fish feeding and supplementary feed on plankton dynamics, and • identify the basic problems associated with cage culture in Lake Elen, Ethiopia.
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Description of the study area : Lake Elen (8 022.1`N, 38 056.6`E) situated at an altitude of 1598 m asl in the Alem Tena area, about 117 km East of the capital city Addis Ababa. It has as area of 250 ha and a mean depth of 2 m. According to the information from the local people, this lake was formed only 40 years ago due to the overflow of Awash River to Dereq Wenz River. Lake Elen is thus fed by the Awash and Dereq Wenz Rivers and is turbid due to the presence of mixing currents and wind action. The major rainy period in the area is between June and September, with a monthly total of more than 224.7 mm. March and January are wet and dry months of the study year, respectively. Short rain occurs in the region during March to April when the highest daily maximum temperature is 30 0C. The period between March and June is the warmest.
Materials and methods Site selection : A convenient site was selected based on different criteria like security, appropriate depth, and accessibility to the lake. Three sites (one at the experiment site, one at the middle, and one at the opposite side of experiment site: Site 1, Site 2 and Site 3, respectively) were selected as sites for cage suspension and for limnological sampling. Cage construction : Cages were constructed from a galvanized wire mesh with a mesh size of 1x½ cm and from weathered tractor tyre rims. The radius of the frame is 0.65 m and the height of the cage is 0.9 m hence the volume of each cage is 1.194 m 3. The connecting structure for the cages is also a stretched galvanized wire and each cage has cylindrical shape (Figure 1). Wire mesh was selected due to its availability in the market, resistance to fish predators like otter and monitor lizard, and prevention of damage by waves.
Fig. 1 : Wire cage used in this study.
Landing stage construction : Landing stage was constructed at the experiment site for suspending the cages and to provide easy access to their monitoring. It was totally constructed from wood, and drums were used to keep the landing stage floating. The advantage of floating landing stage is to move the cages up and down by following the water level in order to keep 1 m 3 of the cage volume always under water. Juvenile collection : Juveniles were collected from another lake, Lake Babogaya, because of the difficulty of using beach seine in Lake Elen.. Juveniles of 30 g mean weight size were collected by using beach seine of 50 m length, 2.5 m width and 20 mm stretched mesh size. Small-sized juveniles were selected by using the cage and the large ones by scoop net and hand picking. The collected juveniles were transported in polyethylene bag with oxygen to the site on the same day and stocking in cages was done with gradual acclimatization. The polyethylene bag with juveniles was immersed in the lake water at the stocking site for 30 minutes to acclimate to the new water temperature, and water from Lake Elen was poured inside slowly. This minimized the death of juveniles due to temperature shock. Weighing and measuring of juveniles were done two days later.
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Stocking in cages was done starting from 50 to 200 fish per cage and one control treatment with 100 fish stocking density. Stocking densities were coded as follows: Ta: 50 fish/m 3; Tb: 100 fish/m 3; Tc: 150 fish/m 3; Td: 200 fish/m 3 and Te: 100 fish/m 3 without supplementary feed (control). Control groups for each stocking density could not be set due to juvenile shortage and 100 fish/m 3 stocking density is taken as a control group by using the available number of juveniles. All treatments were in duplicates. Cages were installed in such a way that they all had equal access to natural food and water circulation. Feeding : This was done for four treatments (Ta, Tb, Tc and Td) was done at a rate of 5% of body weight of fish per day at 6:00 am to 8:00 am, when the water is calm. This avoids flushing out of the feed from the cages by wave (Diana et al., 1996). Due to lack of prepared food for fish in Ethiopia, locally available food was used. Feed ration was placed in a demand feeder, which were suspended at mid depth in each cage and adjusted at two weeks interval based on fish growth and mortality. Sampling: With regard to Physico-chemical parametersWeather data such as air temperature and rainfall were obtained from the Alem Tena meteorological station. Surface water temperature was measured monthly starting from December 2006 to May 2007 with a thermometer. Secchi disc visibility was measured monthly at the three sites with a Secchi disc of 20 cm diameter. Visibility was calculated as the average depth at which the Secchi disc disappeared when lowered and the depth at which it reappeared when raised in the water (Boyd and Turcker, 1992). Fish weight and length measurements from each cage (25%) were done by using a digital weight balance (Ohaus portable balance) and measuring board starting from the date of stocking (February 10, 2007) to final harvest (May 9, 2007), at two weeks interval. Measurements were done at the same time before noon so as to prevent weight variation due to differences in stomach fullness during sampling periods. Data analysis: Fish growth was computed by taking out 25% of the fish from each cage and weights and lengths were taken every two weeks. Weight gain, survival rate, daily growth rates (DGR), specific growth rates (SGR) and relative growth rates (RGR) were calculated using the following formulae:
No . of stock − No . of death Survival rate (%) = X100 No . of stock
Final weight (g) − Initial weight (g) DGR (g / fish / day ) = No . of culture days
ln final weight (g) − ln initial weight (g) SGR (/ day ) = , No . of culture days
and expressed in percentage.
Final weight (g) − Initial weight (g) RGR (%) = X100 Initial weight (g)
Growth rate was also computed at each sampling period to see the difference in growth pattern between each sampling period. Fulton Condition Factor (FCF) was calculated with the following formula and average values were taken at each sampling period for all treatments (Bagenal and Tesch, 1978).
TW FCF = X100 TL 3 Where: TW is weight in gram TL is total length in centimeter. Page | 51
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FCF for different culturing periods were computed by using the same procedures to see the growth level at which the cultured fish have better condition.
The variation of condition factor between different sampling dates was tested by multiple comparisons of means. Feed conversion ratio (FCR) was calculated from the number of kilos of feed that were used to produce one kilo of whole fish. The basic principle in feeding is that the fish should be fed exactly to satiation. If they are fully fed, the fish are not stressed and they provide high quality food for human consumption. For this study, FCR was computed by the formula in Abdelghany (2000).
Feed taken (Kg ) FCR = Weight gain (Kg )
Statistical analysis : Analysis of variance (ANOVA) was used to determine the differences between treatments in mean and final weights, production (yield), growth rate, FCR, survival rate and plankton abundance. Multiple comparisons of means for FCF were done using the GT2-and T- methods (Sokal and Rolf, 1981). All statistics was done using SPSS (SPSS, Chicago. Illinois, USA) and MINITAB, and all tests are considered significant at P<0.05.
Results Physico-chemical parameters : The highest mean water temperature during the study period was 25.7 0C in May 2007 and the lowest was 21.4 0C in January 2007. Mean water temperature decreased from December 2006 to January 2007 and increased up to May 2007. In addition, water temperature was significantly different (P<0.05) at different sampling periods, but not between sites (P>0.05).The maximum Secchi depth (20 cm) was measured in December 2006, then after, it decreased considerably and reached the minimum 0.17 m in May 2007. During all sampling periods Secchi depth was not significantly different in all sites since the 95% confidence level overlaps noticeably. Growth performance : Growth performances for each replicate of each treatment were computed as DGR, SGR, RGR and final biomass. There was no significant variation between replicates of similar treatments (P>0.05); so, pooled samples of replicates were used for all parameters. Tables 1 summarizes the growth performance of cultured Nile tilapia during the study period. There was a slight difference in initial weight; total length and FCF among the treatments but all treatments were not significantly different in mean weight and length (P>0.05). The final mean weight and FCF were calculated after 87 days of cultivation and were found to be significantly lower at higher stocking density (P<0.05). All growth rate parameters DGR, SGR and RGR were inversely related with stocking densities. The highest and lowest growth rate parameters were observed in Ta (50 fish/m 3) and Td (200 fish/m 3), respectively, among the feeding treatments (Table 1). In addition, mean feed conversion ratio (FCR) increased with increasing stocking density. The highest and the lowest FCR were obtained in Td and Ta, respectively (Table 1). However, survival rate of caged Nile tilapia is high in all treatments and ranged from 95.5% in Te to 98.75% in Td.
Table 1 : Growth performance of Nile tilapia in cage culture system in Lake Elen
Parameters Ta Tb Tc Td Te control Stocking density (No/m 3) 50 100 150 200 100 Sample size (n) 24 50 74 99 52 Initial weight (g) 30.38+ 0.66 a 30.52+0.48 a 31.09+0.39 a 29.27+0.33 a 30.63+0.52 a Final weight (g) 139.66+0.65 a 136.31 a 127.69+0.37 b 119.94+0.43 c 111.52+0.52 d Initial length (mm) 100 + 0.8 a 103.12 + 0.52 a 101.35+0.44 a 99+78+0.37 a 101+0.61 a Final length (mm) 157.04 +0.3 156.16 + 0.36 155.40+0.19 153.71+0.52 151.69+0.344
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Daily Growth Rate 1.26 + 0.0 a 1.23+ 0.002 a 1.10+ 0.01 c 0.99+0.008 d 0.94+0.00 d (DGR) (g/day) Specific Growth Rate 1.8+0.02 a 1.7+0.02 a 1.62+0.01 1.58+0.018 1.5+0.14 (SGR) (%/day) Relative Growth Rate 362.1+10.8 351.22+7.41 311.25+4.14 300.1+6.51 275.05+5.39 (RGR) (%) Survival rate (%) 97 96.5 98 98.75 95.5 Feed Conversion Ratio 3.05 3.14 3.32 3.44 ** {FCR) Initial Fulton Condition 2.43+0.02 2.34+0.02 2.45+0.01 2.39+0.03 2.37+0.02 Factor (FCF) Final Fulton Condition 3.6+0.014 a 3.6+0.015 a 3.37+0.01 3.26+0.039 b 3.26+0.011 b Factor FCF Initial fish biomass 1.52 3.05 4.66 5.86 3.02 (Kg/cage) Final fish biomass 6.77 13.25 18.62 22.90 10.65 (Kg/cage) Fish biomass gain 5.25 10.20 13.96 17.04 7.65 (Kg/cage) Net yield per individual 108.34 105.69 94.97 86.08 80.48 fish (g/fish/cage) *Data are shown as means with standard error. Means in row followed by the same superscript are not significantly different (P<0.05). **No supplementary feed, no data. Ta: Treatment a, Tb: Treatment b, Tc: Treatment c, Td: Treatment d, Te: Treatment e
Mean weight : The maximum and minimum mean final weights were achieved in Ta (139.66 g) and Te (111.52 g), respectively. However, from the feeding treatments, the minimum mean final weight was found in Td. Tb had significantly higher final mean weight (P<0.05) than Td, despite their equal stocking density. At harvest, the maximum and minimum fish biomass per cage was in Td (22.9 kg/cage) and Ta (6.77 kg/cage), respectively. The biomass per cage calculated for the non-feeding treatment (Te) was significantly lower than the feeding treatment (Tb) despite their equal stocking density (P<0.05). The difference in the mean weight increased as the culture period extended. Up to the third sampling period (February 28), there were no significant differences (P>0.05) between all treatments. The variation in the mean weight of fish between treatments widens as the culture period extends after February 28 onwards (Fig. 2). Moreover, mean weight of cultured fish decreased with increasing stocking density (Fig. 2, Table 1) for all sampling periods. The net fish biomass was computed for all treatments after harvest. The leading treatment was Td giving a net yield of 17.04 kg/cage followed by Tc, Tb, Te and Ta (Table 1). But the net yield per individual fish was highest in Ta (108.34 g/fish) followed by Tb, Tc, Td, and Te. Net yield per fish was negatively affected by stocking density. The feeding treatment Tb had significantly higher net yield/fish than the non-feeding treatment Te, regardless of their equal stocking density. Daily growth rate (DGR) : The mean DGR computed for 87 days of culture and between all sampling periods showed decrease with increasing stocking density (Table 1). Ta had significantly higher mean DGR (P<0.05) than other treatments, except Tb. Among the feeding treatments the maximum and minimum average DGR were 1.26g/individual/day (Ta) and 0.99g/individual/day (Td), respectively. However, despite equal stocking density, the feeding treatment Tb attained significantly higher mean average DGR than the non-feeding treatment Te (P<0.05). DGR at all sampling periods was negatively affected by stocking density. Mean DGR were significantly different between each sampling period of treatments (P<0.05). But Ta and Tb were not significantly different in their daily growth rate (mean) at growth rate between February 10 and February 28 (P>0.05).
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s 140 Treatment Ta Tb Tc 120 Td Te
100
80
Mean weight (g) weight Mean 60
40
20 10-Feb 19-Feb 28-Feb 19-Mar 31-Mar 21-Apr 9-May Sampling date
Fig. 2 . Variations in mean weight of caged fish in all treatments during the culture period
Specific growth rate (SGR) : The mean SGR is inversely related with stocking density (Table 1). From the feeding treatments Ta (1.8/day) and Td (1.6/day) attain the maximum and the minimum mean average SGR, respectively, whereas the smallest average SGR of all treatments was that of Te (1.5/day). There was no significant difference between Ta and Tb (P>0.05). However, Tb had statistically higher mean average SGR than Te (P<0.05), despite their equal stocking density. The SGR at all culture periods decreased with increased stocking density for all treatments. In addition, with equal stocking density, Tb has higher mean SGR than Te (P<0.05) in all sampling periods. The largest mean SGR was observed in the first growth period (February 10 to February 19) in all treatments and the lowest was at the last growth period (April 21 to May 9).
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Relative growth rate (RGR) : Table 1 shows the decrease in mean RGR with increased stocking density. The highest mean RGR was obtained in Ta (362.1%) and the smallest was in Te (275.05%). The least RGR was reached in Td (300.1%) among the feeding treatments. Ta and Tb (351.22%) had significantly higher RGR than Tc (311.25%), Td, and Te. Despite their equal stocking density, Tb had significantly higher RGR than Te. Fulton condition factor (FCF) : The maximum FCF for all treatments was 3.6 and the minimum was 2.34 in Ta and Tb at the sixth and the first sampling period, respectively. FCF increases with increasing culture period up to the sixth sampling period. FCF was statistically different between sampling periods in all treatments (P<0.05). Despite their equal stocking density, Tb had significantly higher mean FCF than Te (P<0.05). In all sampling periods, FCF decreases as the stocking density increases (Fig. 3). Ta had the highest mean FCF followed by Tb, Tc, Td and Te.
4.0 FCF1
3.5 FCF2
FCF3 3.0
FCF4
2.5 FCF5 Mean+-2 SDFCF
2.0 FCF6
1.5 FCF7 Ta Tb Tc Td Te
Treatment
Fig. 3 . Fluctuation in Fulton condition factor of caged fish for each treatment during the study period.
Feed conversion ratio (FCR) : As shown in Table 2, the amount of feed given per fish per day decreased with increasing stocking density. The maximum and minimum overall feed conversion ratios (FCR) were computed in Td (3.44) and Ta (3.05), respectively. FCR increased as the culture period extended and is significantly different among culture periods (P<0.05) and decreases with increasing stocking density (Table 2)
Discussion Water quality parameters measured during the study period remained in agreement with the favorable range set for Nile tilapia (Boyd, 1990). Surface water temperature in all sampling sites ranged from 21.4 0C in January 2007 to 25.7 0C in May 2007. This range was found out to be similar in some of other Ethiopian lakes; Ziway (18.5-27.5 0C Girma Tilahun, 1988), Babogaya (20.5-28.4 0C; Yeshimebet Major, 2006), Hawassa (23.8-28.4 oC; Demeke Kifle, 1985).
.
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Table 2 : Mean weight, feeding rate and Feed Conversion Ratio (FCR) of fish for each culture period .
Feb. 10- Feb. 19 - Feb. 28 - Mar. 19 Mar. 31 April 21 Feb 10 - Treatment Parameter 19 28 Mar. 19 - 31 -Apr. 21 - May 9 May 9 Ta Mean weight 30.38 42.25 53.93 77.05 92.16 118.06 (g) Feed/fish/day 1.52 2.11 2.7 3.85 4.61 5.9 333.17 FCR 1.15 1.63 2.22 3.06 3.74 4.92 3.05 Tb Mean weight 30.52 43.56 55.08 77.7 92.63 117.83 Feed/fish/day 1.53 2.18 2.75 3.89 4.63 5.89 335.59 FCR 1.05 1.7 2.31 3.12 3.86 5.44 3.14 Tc Mean weight 31.09 43.17 53.98 73.15 86.83 109.5 Feed/fish/day 1.55 2.16 2.7 3.66 4.34 5.48 318.31 FCR 1.16 1.8 2.67 3.21 4.02 5.73 3.32 Td Mean weight 29.28 41.33 51.94 68.56 80.82 100.78 Feed/fish/day 1.46 2.07 2.6 3.43 4.04 5.04 297.81 FCR 1.09 1.75 2.97 3.35 4.25 5.98 3.44
In the present study replicates of all treatments had significantly similar growth performance and data from pooled samples of replicates were analyzed. The results of this experiment revealed that fish survival was reasonably good in all stocking densities and ranged from 96.50% to 98.75%. This finding indicates that stocking density might have a limited or no effect on fish survival. Similar results have been reported by Dambo and Rana (1992) who found survival of Nile tilapia fry ranging from 94.5% to 100% at stocking densities of 2 to 20 fry L-1. Growth performance of caged Nile tilapia could be affected by food availability, environmental parameters, disease, stocking density, physiological status, and reproductive state (Lovell, 1981). The negative and positive effect of stocking density and additional feed, respectively, on growth performance of caged fish, resulted in the variation of mean final weight between treatments. The final mean weight of caged Nile tilapia in the low-density treatment (Ta) (139 g), which was the highest in this study, was smaller than that reported by Yi et al . (1996). This might be due to the smaller stocking size (30.38 g) and shorter growing periods (87 days) compared with Yi et al. (1996) (141-152 g for 90 days). Studies on other fish species showed that stocking density has either positive or negative effect on the gross yield per cage and net yield per individual, respectively (Honer, et al., 1987; Suresh and Lin, 1992). In this study, all feeding treatments had higher net yield per individual than the non-feeding treatment, regardless of their stocking density. This justifies the positive effect of supplementary feed on the growth of fish. Contrary to this result, Moav (1977) reported similar production between fish with and without supplementary feed in fertilized fresh water polyculture ponds. This seems more likely to be due to lower densities of stocked fish (Diana et al ., 1994) or type of food used. The net yield per individual obtained in this study from the non-feeding treatment is attributed mainly to the presence of large amount of natural food in the lake. Coche (1982) maintains that in some cases, natural food (plankton) might be sufficient without any supplementary feeding required in cages. Net yield per individual is a function of growth rate of caged fish (Suresh and Lin, 1992). Weight gain of caged Nile tilapia in this study lies in the range reported previously for intensive cage culture of Nile tilapia in ponds (0.56-2.49 g/individual/day) (Guerrero, 1979; McGinty, 1991). Growth parameters (average DGR, DGR, average SGR, SGR and RGR) are known to be affected negatively by stocking density and positively by supplementary feeding (Diana et al., 1994; Kebede Alemu, 2003). This is also supported in this study, where the maximum average DGR was observed in the low stocking density treatment (Ta) (50 fish/cage). This is also in agreement with Huang and Chiu (1997) who studied the effect of stocking density for Nile tilapia fry. The negative effect of stocking density on growth 56 Ma nagement of shallow water bodies ..., EFASA 2010 parameters was also found in other fish species, such as Chinook salmon (Martin and Wertheimer, 1989), African catfish (Haylor and Pascual, 1991) and Turbot, Scophthalmus maximus (Irwin et al ., 1999). The condition or well-being of fish is influenced by environment, food quality and quantity, rate of feeding, disease and reproductive activity (Bowen, 1979; Getachew Tefera, 1987). The condition of caged fish in this study was much better than the condition of similar fish in other Ethiopian natural lakes as reported by different workers. For instance, Demeke Admassu (1990) found the condition of Nile tilapia in Lake Hawassa as 1.3 to 2.12, which is lower when compared to this study (2.34 - 3.6). This is because caged fish do not spend much energy in activities like reproduction and swimming. In addition, supplementary feed and the productivity variation between the lakes might be another reason for this difference, but this needs further investigation In this study, better fish condition was recorded at lower stocking density. This indicates the negative effect of stocking density on condition of caged fish. This is attributed to increased competition for food and space with increased stocking density. The condition of fish at harvest was significantly higher in Ta and Tb than other treatments. Previously, Huang and Chu (1997) also found that FCF ranged from 2 – 3.4 and that was negatively affected by stocking density. The high condition of all feeding treatment than the non-feeding one indicates the positive effect of supplementary feeding on the condition of fish. FCR is affected by accessibility of food for fish, nutritional status of food, environmental parameters, stocking density and physiological aspect of fish (Abdel-Tawwab, 2004). Low FCR and best feed conversion efficiency was observed in Ta (50 fish/cage) in the present study, as was also found by Jauncey (1982); Ofojekwu and Ejike (1984) and DeSilva and Perera (1985). FCR increased with extending culture periods or fish size increase and it ranged from 1.46 – 1.52 (Feb 10 - 19) to 4.92 - 5.98 (April 21 – May 9). This trend was in agreement with the result obtained by Al-Hafedh and Siddiqui (1998) and Khattab et al . (2000). Akbulut et al . (2003) also reported the positive correlation of FCR with stocking size in trout cage culture. The decrease of feed conversion efficiency or increase of FCR with size increase might be due to the decline of the fish plankton filtration efficiency with size. Caulton (1977) and Brummet (1995) found that small tilapia filter significantly more phytoplankton than larger individuals. In addition, the feeding rate relative to body weight decreases as fish size increases; however, the rate of food consumed increases per individual (Wang et al ., 1985). Generally, the result of this study showed the negative effect of stocking density on fish growth performance, condition, feed conversion efficiency and net yield per fish and positive effect on gross yield. Survival of fish in this study was not affected either by stocking density or by supplementary feeding. This study also verified the positive effect of supplementary feeding on the growth performance and net yield per fish in the cage culture at Lake Elen, and that supplementary feed added did not cause an adverse effect on the lake plankton ecology.
Acknowledgements We are indebted to the Department of Biology, Addis Ababa University for providing vehicle and some additional fund. The Ethiopian Society for Appropriate Technology (ESAT) is gratefully appreciated for providing the major funding through Prof. Shibru Tedla. We thank the Systematic Research Fund of the American Museum of Natural History and Development Innovation Fund of the Zoological Natural History Museum of the Addis Ababa University for the financial assistance through Dr. Abebe Getahun. Special appreciation is also extended to the staff members of Sebeta National Fisheries and Other Living Aquatic Research Center for their kind support in logistics.
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Diana, J., Lin, C. and Yi, Y., (1996). Timing of supplemental feeding for tilapia production. J. World Aquacult. Soc. 27, 410-419. Edwards, P., (1986). Duck-fish integrated farming systems. In: Duck Production, Science and World Practice . Farel, D. and Stapleton P. (eds.), pp. 269-291. University of New England. Edwards, P., (1991). Integrated fish farming. Info. fish Int. 5, 45-5 1. Fernando, C., (2002). A Guide to Tropical Freshwater Zooplankton: Identification, Ecology and Impact on Fisheries. Backhuys Publisher. Leiden. Netherlands. pp. 291. Ganf, G., (1974). Diurnal mixing and vertical distribution of phytoplankton in shallow equatorial lake (Lake George, Uganda). J. Ecol. 62, 611-629. Getachew Tefera, (1987). A study on an herbivorous fish, Oreochromis niloticus L., diet and its quality in two Ethiopian Rift Valley lakes, Hawassa and Zwai. J. Fish Biol . 30, 439-449. Girma Tilahun, (1988). A seasonal study on primary production in relation to light and nutrients in Lake Ziway, Ethiopia. M.Sc. Thesis, Addis Ababa University, Addis Ababa, pp. 62. Guerrero, R., (1979). Cage culture of Tilapia in the Philippines. Asian Aquaculture 2, 6. Haylor, G. and Pascual, A., (1991). Effect of using ram testis in a fry diet for Oreochromis niloticus (L.) on growth, survival and resultant phenotypic sex ratio. Aquaculture Fishery Managment 22, 265-268. Hotzel, G. and Croome, R., (1999). A phytoplankton Methods Manual for Australian Freshwaters . Land and Water Resource Research Development Corporation. Canberra. Australia. pp. 51. Huang, W. and Chiu, T., (1997). Effects of stocking density on survival, growth, size variation, and production of Tilapia fry. Aquaculture Research 28, 165-173. Irwin, S., Halloran, J. and Fitzgerald, R., (1999). Stocking density, growth and growth variation in juvenile turbot, Scophthalmus maximus (Rafinesque). Aquaculture 178, 77 - 88. Jauncey, K., (1982). The effects of varying dietary protein level on the growth, food conversion, protein utilization and body composition of juvenile tilapias ( Sarotherodon mossambicus ). Aquaculture 27, 43-54. Kebede Alemu, (2003). The growth performance of Oreochromis niloticus reared in freshwater ponds loaded with varying levels of poultry manure. SINET Ethip. J. Sci. 26, 17-23. Khattab, Y., Abdel-Tawwab, M. and Ahmad, M., (2004). Effect of protein level and stocking density on growth performance, survival rate, feed utilization and body composition of Nile tilapia fry (Oreochromis niloticus L.). In: Proceeding of the Sixth International Symposium on Tilapia in Aquaculture . pp. 264–276. BFAR, Philippines. LFDP, (1996). Proceedings of the National Fisheries Seminar, Ziway. November 1995. Lake Fisheries Development Project Working Paper no. 21 LFDP, (1997). Fisheries statistical bulletin No. 4. Addis Ababa. Ministry of Agriculture. Lin, C., Jaiyen, K. and Muthuwan, V., (1990). Integration of intensive and semi-intensive aquaculture concept and example. Thai Fisheries Gazette 43, 425-430. Lovell, R., (1981). A Laboratory Manual for Fish Feed Analysis and Fish Nutrition Studies. Department of Fisheries and Allied Aquaculture, Auburn University, AL, USA. Martin, R. and Wertheimer, A., (1989). Adult production of Chinook salmon reared at different densities and released as two smolt sizes. Prog. Fish cult. 51, 194-200. McGinty, A., (1991). Tilapia production in cages: effects of cage size and number of non-caged fish. Prog. Fish. Cult. 53, 246-249. Ministry of Agriculture (MOA), (2001). The Federal Democratic Republic of Ethiopia: Country Fisheries Profile and Fisheries Management. (unpublished). pp 91. MINITAB, (2003). Version 14 . Minitab Inc. USA. Moav, R., (1977). Intensive polyculture of fish in freshwater ponds: Substitution of expensive feeds by liquid cow manure. Aquaculture 10, 25 – 43. Moriarty, C. and Moriarty, D., (1973). Quantitative estimation of the daily ingestion of phytoplankton by Tilapia nilotica and Haplochromis nigripinnis in Lake George, Uganda. J. Zool. 171, 15-23. Ofojekwu, P. and Ejike, C., (1984). Growth response and feed utilization in the tropical cichlid, Oreochromis niloticus (L.) fed on cotton seed based artificial diets. Aquaculture 42, 27-36.
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Omar, E., (1994). Optimum protein to energy ratio for tilapia (Oreochromis niloticus) fingerlings. Alex. J. Agric. Res., 39, 73-93. Papst, M., Dick, A., Arnason, A. and Engel, C., (1992). Effect of rearing density on the early growth and variation in growth of juvenile Arctic charr, Salvelinus alpinus (L.). Aquaculture and Fisheries Management 23, 41-47. Prescott, G., 1962. Algae of the western Great Lakes area . Wm. C. Brown Co. Dubuque, Iowa, pp. 977 Sokal, R. and Rolf, F., (1981). Biometry 2 nd edn . W.H. Freeman and Company. New York. pp. 859. Suresh, A. and Lin, C., (1992). Effect of stocking density on water quality and production of red tilapia in a recirculated water system. Aqua. Eng. 11, 1-22. Talling, J. and Rzóska, J., (1967). The development of plankton in relation to hydrological regimes in the Blue Nile. J. Ecol . 55, 637-662 Tekalign Mamo, Abiye Astatke, Srivastava, K. and Asegelil Dibaba, (1993). Improved management of vertisols for sustainable crop-livestock production in the Ethiopian highlands: Synthesis reports 1986-92. Technical committee of the joint vertisol project, Addis Ababa, Ethiopia. Wang, K., Takeuchi, T. and Watanabe, T., (1985). Effect of dietary protein levels on growth of Tilapia nilotica . Bull. Jap. Soc. Sci. Fish . 51, 133-140. Whitford, L. and Schumacher, G., (1973). A manual of Freshwater Algae . Sparks Press. Raleigh. N.C. pp. 323 Wood, R. and Talling, J., (1988). Chemical and algal relationships in a salinity series of Ethiopian inland waters. Hydrobiologia 15, 29-67. Yeshimebet Major, (2006). Temporal changes in the community structure and photosynthesis of phytoplankton in Lake Babogaya, Ethiopia. Unpublished MSc. Thesis . Addis Ababa University. Yi, Y., Lin, C. and Diana, J., (1996). Influence of Nile tilapia ( Oreochromis niloticus ) stocking density in cages on their growth and yield in cages and in ponds containing the cages. Aquaculture 146, 205–215. Zonneveld, N. and Fadholi, R., (1991). Feed intake and growth of red tilapia at different stocking densities in ponds in Indonesia. Aquaculture 99, 83-94.
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Pond fish farming in practice: Challenges and opportunities in the Amhara Region
Chalachew Aragaw: Fisheries and Aquaculture Extension Expert, Amhara National Regional State, Bureau of Agriculture and Rural Development, Bahir Dar, Ethiopia. Email: [email protected]
ABSTRACT: The purpose of this paper is to provide comprehensive information on the recent development of pond fish farming in Amhara National Regional State mainly for the purpose of improving food security at farmers’ household level. Fish farming in Amhara Region started in 2004 (1996 Eth.C.) by the Bureau of Agriculture and Rural Development in the central part of the regional state after launching a campaign to promote pond fish farming. The response was encouraging and the interest of fish farming among the fish farmers is now increasing with continuous education and support from Bureau of Agriculture and fisheries officers at all levels.Pond fish farming is gradually taking momentum; currently there are about 250 pond fish farmers. The pond sizes vary from 100m 2 – 400m 2. Transportation of fingerlings is done by using oxygenated plastic bags and plastic pail. The stocking rate for Nile Tilapia fingerlings is 2 /m 2 and the average weight stocked was 10g to 15g. We collected tilapia fingerlings from Lake Lugo and Geray Reservoir using a seine net. From the beginning, the region introduced about 130,953 fingerlings into one lake, two reservoirs, and the rest in farmers’ ponds with an average introduction of 21,826 fingerlings/year . In most cases, during fingerling transportation, mortality was almost none per plastic pails except in exceptional cases which was below 3%. Pond management system in Amhara region is extensive. Predator has not been a problem so far. But 3 years ago in three farmers’ fish ponds of Awi administrative zone, a large infestation of frogs were found after seining. Pond fish is harvested between 8 to 12 months. Partial harvesting is usually done using mosquito seine nets and gill nets used as seining. The length of the gill net is 12m. to 15 m. with stretched mesh size of 4cm to 6cm. The average size of Tilapia harvested is between 200g and 300g. Only marketable size is selected and the rest are returned to the pond. In the region, fish farming development is encouraging, but the region has faced many challenges. Scarcity of fingerlings to satisfy the increasing demand is among one. There is an urgent need for establishment of one fish hatchery center at the central part of the region. It is believed that the transfer of fish farming technology and knowledge should be promoted through pilot projects as well as foreign collaboration and assistance is necessary to develop fish farming in the region.
Key words : Amhara region, pond farming
Introduction Fish farming is becoming a huge global issue, with human population increasing and natural fish stocks reaching their production limits, the gap in the supply must come from somewhere, aquaculture. Governments or companies of many countries that enter into this field not only can produce food for their country but an export market is readily available, not only providing jobs also a boost to the country. Aquaculture output, growing at 11 percent a year over the past decades, is the fastest growing sector of the world food economy. Climbing from 26.8 million tons produced in 1996 to 47.8 million tons in 2005 (excluding plants). China, where fish farming began more than three thousand years ago, accounted for 30.6 million tons (64%) of the 47.8 million tons of the world. India is the distant second with 2 million tons and other developing countries include Bangladesh, Indonesia, and Thailand follow. Among industrial countries, Japan (8000, 000 tons), the United States of America (450,000 tons), and Norway (400,000 tons) are the leaders (Chalachew, 2004) 2. If world fish farming production grows constantly as the current situation, it will overtake natural fish stocks production very soon.
2 Chalachew Aragaw 2004. Integrated Small-scale Fish Farming: A Training Manual. Bureau of Agriculture and Rural Development for Amhara Region. 61 Ma nagement of shallow water bodies ..., EFASA 2010
.2 90 6.8 4.2 4 8 8 84.5 85.8 8 81.5 80
70
60 .8 5 7 7 5. 4 4 2. 4 50 0. 4 5 .9 4 5. 7 Farmed fish 3 3 40 Natural fish 30
Fish production in tons 20
10
0 2000 2001 2002 2003 2004 2005
Fig. 1 : Growth of world fish farming as compared to fish production (in tons).
Fish farming can be more beneficial if it is integrated with other agricultural systems. Integrated fish farming is the practice of growing fish and other agricultural enterprises together. This farming system has advantages over other systems in that a by-product from one enterprise is made an input into another product with recycling of resources (Malawi National Aquaculture Centre, 2004). 3 Systems range from the very simple: fish with one kind of crop/domestic animal, to much more complex: fish with crops and animals. Although fish farming have been practised in many countries of the world for many years, it is only beginning in our country and particularly in the regions.. The land and the waters of our regional state are very favourable to expand fish farming from cold to warm water fish species (FAO, 19950) 4. The Region’s standing surface water resources, comprised of many lakes, reservoirs, and rivers can provide numerous opportunities for integrated fish farming throughout the regional state. For integrated fish farming we need land, reliable water, labour, etc., which we have all in our region. Therefore, it is good opportunity for farmers to integrate fish farming with other agricultural activities so that the farmers will get daily income from the sales of fish, vegetables, fruit, chicken and the like. Studies conducted in many countries show that fish farmers are more food secure than non-fish farmers because they make up for yield losses using pond-irrigated crops and vegetables.
Fig. 2 : A farmer in Libo Kemkem Woreda with his fish pond integrated with fruit and crop
3 Malawi (Domasi) National Aquaculture Centre 2004. Fish farming training manual (July 26-August 7/2004). 4 FAO 1995. Review of Fisheries and Aquaculture: Ethiopia. FAO Fisheries Circular No. 890 FIPP/C890 62 Ma nagement of shallow water bodies ..., EFASA 2010
Materials and methods Historical evelopments of fish farming in the Region : Fish farming in Amhara Region started in 2004 (1996 Eth.C.) by the Bureau of Agriculture and Rural Development in the central part of the regional state after launching a campaign to promote pond fish farming. The response was encouraging and the interest of fish farming among the fish farmers is now increasing with continuous education and support from Bureau of Agriculture and fisheries officers at all levels. This campaign includes: • Promotion including advertising and consumer education through media; • On job training in Farmers Training Centre (FTC); • Field visits during farmer’s day; • Supply of fingerlings free of charge (purchase of fish transportation equipment) and • Provide free of charge advisory services on the location, size and building procedure of the ponds. Location (Site selection): I t is believed that the success of fish farming operation depends upon the suitability of the site where ponds will be constructed. In choosing a suitable site for pond construction, we advice farmers to consider the following preconditions: • Topography of the land, • Water supply, • Soil, • Access or proximity of the house Topography : The site should have a gentle slope, to allow filling and draining of the ponds by gravity. This saves money unlike pumping, which needs operational costs. Wide gently sloping valleys are the best, while narrow deep sloping valleys are usually not suitable for constructing fishponds. Areas prone to flooding are not suitable for fishpond construction. Water : The water source should be perennial with enough water all the year round to fill the pond and to compensate for losses due to seepage and evaporation. The quantity of water available will, amongst other factors, determine the size and number of fishponds. Seasonal rivers and streams are not recommended as direct source of water for fishponds. Soils : Soil with too much sand or gravel will not hold water. The best soils for fish farming are the sandy clay, loamy clay and clay soils. Site access and proximity to the house: The site should be close to the farmer's home for easy pond management and reducing risk of theft and predation. Pond Construction : It is very important that fishponds are properly constructed. A pond is not just a hole dug in the ground, but a properly constructed structure for raising fish. When constructing ponds, we advise the farmers to include pond inlet and outlet structures; an inlet, to let water into the pond and an outlet to let water flow out of the pond. Water depth in the pond should be at least 1 to 1.5m at the deepest end and 0.7 to 1 m at the shallowest end. There should be a freeboard of 15 cm to 30 cm between the top of the wall and the water level. Farmers are encouraged to construct ponds of minimum size 100m 2 (10 x 10 m). Experience has shown that most farmers find it convenient to construct and manage ponds of this size. Considerations made before constructing a pond • The pond should be filled with water by gravity. • The pond should hold water • The pond should be easily drained during harvesting Planting grass: When pond digging is completed, we encourage farmers to plant grass on the dikes as a protection to reduce erosion but not trees or shrubs as the roots can cause seepage. Pond filling : Once the construction is completed, the farmers fill the pond slowly with water. In most cases a screen (perforated tin or piece of meshed iron sheet) are fitted at the water inlet to stop predators and their eggs from entering the pond. Ponds are not allowed to be filled level with the pond wall. Farmers leave a free board of 15-30 cm between the top of the pond wall and the water level.
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Pond fertilization : Most of the fish farmers do not feed their fish in the pond. To avoid food shortage they apply cow manure, compost and sometimes poultry droppings. Fertilization is aimed at developing natural food and saving artificial feeds (to minimize expenditure). Fertilization means to supply phytoplankton with nutrients for photosynthesis and to promote the growth of phytoplankton, by which zooplankton and fish feed on for their growth. The abundance of phytoplankton and zooplankton provide fish with abundant natural feeds, by which they can grow faster and the yield of fish pond increase thereby. Fish transportation : We give practical training for zonal and woreda fishery officers the key technology of collecting, packing, transporting fish seeds with oxygen bags for near and far distances, releasing fish seeds to ponds and handling of the seeds during transportation and collection. Fish seeds are given freely. We collect tilapia fingerlings from Lake Lugo and Geray Reservoir using a seine net. Transportation of fingerlings is done by using oxygenated plastic bags and plastic pail. About half of the plastic bag is filled with clean water and fingerlings are stocked. The stocking rate is 200 to 300 fingerlings per bag depending on the distance of the farmers’ pond. Then oxygen is added and the bags are tied with a rubber band or rope. The bag is then placed in plastic pail for ease of carrying and to avoid rupture of the plastic bag. In this method a lot of fingerlings can be transported at one time. For example, using a double cap car, we can transport 3000 fingerlings at one time. At departure we measure water temperature, average weight, average length and total number of fingerlings. On arrival, we measure pond water temperature and water temperature of the plastic bag that has fingerlings. Before releasing the fish into the pond, the transporting container should be submerged for 10-15 minutes in the pond. This will facilitate gradual exchange/adaptation of fish to the water temperature. Then fish are gradually released from plastic bags upon arrival at the final destination i.e. farmers’ ponds. Fingerling transporting equipment are available in the market except collection nets. The plastic bags are available only in Addis Ababa. The price of a kilo of plastic bag of size 60 cm by 90 cm is Birr 30. We usually use a plastic bag of thickness 8 and or 10 µ; thickness above 10 µ can leak oxygen when tied and below 8 µ doesn’t have strength. A plastic pail of 40 to 60 liters capacity is a good size. The average price is about 80 Birr and it is available at local markets. Oxygen cylinders of 15 to 25 liters capacity is a manageable size and can be available in Addis Ababa for about Birr 2000, excluding the regulator.
Fig. 3 : Fingerlings in plastic bags with oxygen ready for transportation
Pond management : Pond management system in Amhara region is extensive. Ponds are fertilized with various types of manure (poultry, cattle and compost) to enhance natural food growth for the fish feed. Very rarely, fish are fed on wheat, sorghum maize bran, chopped injera and leaves of different types. Supplementary feeds : Just like people, fish like to eat every day. If they are not fed properly they become hungry and growth is retarded. Most of the time farmers are too busy; feeding may be rarely done. But we encourage them to feed fish at least once in a day. Most of fish in ponds depends on natural food in the pond. Formulated fish feeds which are complete balanced diets are not commercially
64 Ma nagement of shallow water bodies ..., EFASA 2010 found in the region. In the region, women involve in pond fish farming activities. Men construct the ponds but once built, it is generally the women who feed the fish and manage the ponds; furthermore a few women involve in fish processing and feed their family. Predator control : Predator has notbeen a problem so far. But 3 years ago in three farmers' fish ponds of Awi administrative zone, a large infestation of frogs were found after seining. In all ponds we could not find fish at all after seining. We drained and limed the pond to restart stocking and the result was again the same. Many research workers warn that frogs of the Xenopus species are notorious in fishponds and can eliminate fish by feeding on fry and fingerlings. A large infestation of frogs in a pond also results in competition for space and food and hence the fish become stunted. Regular seining of ponds and screening of inlets can control frog infestation. Many kinds of animals prey on fish and may cause severe losses to the farmer. It is therefore important to take measures to prevent predation. According to the Egyptian International Center for Agriculture (EICA), (2006), 5 the common predators in ponds include: aquatic insects, crabs, predatory (carnivorous) fish, frogs, monitor lizards, snakes, birds (king fisher, heron, pelicans, cormorants), otters and humans. Harvesting : Fish should be harvested after a production cycle and farmers must adhere to a production cycle, because if the fish are not harvested, the farmer will keep on managing them when they have stopped growing, as a result the farmer does not get any benefit in return. Farmers should harvest fish for sale or home consumption at the right time. Farmers use several fish harvesting methods, which includecomplete harvesting by cutting the pond wall and draining the water or draining with a drainage pump. If there is enough water to refill the pond, we advise the fish farmer to use this method. This method is believed to the best way of harvesting. Partial harvesting by seining is commonly used by the farmers. Nets of 10 to 15 cm length and 1.5 cm width of stretched mesh size 6 cm is commonly used. Some farmers use mosquito nets.
Results and discussions Pond fish farming is gradually taking momentum (energy, drive), currently there are about 300 pond fish farmers with slightly greater than 300 ponds since very few farmers have 2 ponds. The pond sizes vary from 100m 2 – 400m 2. The stocking rate for fingerlings is 2 /m 2 and the average weight of Nile Tilapia fingerlings stocked is 10g to 15g. From the beginning, the region has introduced about 130,953 fingerlings into one lake, two reservoirs, and the rest into farmers’ ponds with an average introduction of 21,826 fingerlings/year (Fig. 4, below) . In most cases, during fingerling transportation, mortality was almost none per plastic pails except in exceptional cases which was below 3%.
45000 43000 40000 Common Carp 35000 (5%) 30000 27075 Nile Tilapia 00 6 (95%) 22 1 25000 89 21826 18 20000 70 132 15000 7 No. of Fingerlings 10000 611 5000
0 1996 1997 1998 1999 2000 2001 6 Years Average Ethiopian Year Fig. 4 : Fingerling distribution trend and the 6 years average cultured fish species (percentage composition).
5 Egyptian International Center for Agriculture, 2006. Warm Water Fish Production, Egypt. 65 Ma nagement of shallow water bodies ..., EFASA 2010
The fish species cultured in ponds are Nile tilapia (>95%) and Common carp (about 5%) that are available in Geray irrigation reservoir in West Gojam and Lake Lugo in South Wollo Administrative Zone, and recently considerable amount of fingerlings were obtained from Bahir Dar Fisheries and other Aquatic Resources Centre. Production period and average size at harvest : Pond fish is harvested between 8 to 12 months. Partial harvesting is usually done using mosquito seine nets and gill nets used as seining. The size of the gill net is 15m to 20 m with stretched mesh size of 4cm to 6cm. The average size of Tilapia harvested is 200g. Only marketable size is selected and the rest are returned to the pond.
60000 50793 Pond Fish Farming 50000 Capture fisheries 44113
40000 30032 30537
30000
20000 12810 Yield in Quintals 10000 12 27 45 54 38
0 2005 2008 2007 2008 2009
Fig. 5 : Fish production trend (Quintals) from fish farming and capture fisheries in Amhara Region
Harvested pond fish are sold fresh locally to the near-by consumers. Some pond fish farmers reported that they sold a single fish for 5-10 Birr. Reservoir fish culture : In line with pond fish farming , culture based fisheries in the reservoirs is considered as very important development issue. This method was practiced in the 1970s in our region. For example Geray irrigation dam, Lake Zengena and Tirba were stocked by the Ministry of Agriculture and Rural Development, Sebeta Fish Research Station. The stocked fish in Geray irrigation reservoir successfully bred and is becoming very important source of fingerlings distribution water body for the region. There are many big reservoirs (man made lakes) that has been constructed and are under construction for various purposes. Therefore, all these man made lakes will have very great potential for fishery development without affecting their primary objectives of construction if they are stocked.
Table 1 : The major reservoirs in the region. (Source: Amhara Bureau of Water Resource Development Bureau 2009) 6 Name of the Purpose of Potential for No. Area (ha.) Status reservoirs Construction irrigation 1 Tekeze Hydro 16000 Hydro power Completed power generation (90% in Amhara region) 2 Koga 600 Irrigation 7000 Completed 3 Megech 1160 „ 7311 Under construction 4 Rib 895 „ 19925 Under construction 5 Jema 737 „ 7786 Under construction 6 Gilgel Abay 1 937 „ 12069 Project study completed 7 Gilgel Abay 2 2452 „ 11508 Project study completed 8 Gumara 1 1200 „ 13979 Project study completed
6 Amhara Bureau of Water Resource Development 2009. Water. no 2. 66 Ma nagement of shallow water bodies ..., EFASA 2010
Name of the Purpose of Potential for No. Area (ha.) Status reservoirs Construction irrigation 9 Gumara 2 1090 „ 13976 Project study completed 10 Tana Beles „ 35500 Project study completed 10 Other 12 240 „ No data completed small reservoirs (average 20ha) 11 Total 25311 128551
Discussion Pond fish farming is recognised by the regional government as an alternative means of achieving food security in the rural community. The farming is becoming of interest for the regional government. Currently the government is promoting pond fish farming in many ways. For example the government is distributing fingerlings freely, conducting technical training and advice, encouraging the private sector to participate and invest, allowing investors to import free of tax and 100% investment ownership. However, much remains to build institutional capacity in the area of research, extension, technology and training which require external assistance. In Amhara region, the status of pond fish farming varies from one administrative zone to another. For example in West Gojam and East Gojam, fish farming is relatively increasing. In all cases it is entirely an extensive farming practice primarily for subsistence. Most of the farmers’ ponds are operated for self-consumption and a few of them for demonstration purpose at Farmers Training Center. Opportunities • Potential for growth of fish farming in the region • There is Federal Aquaculture Development Strategy. • There are lots of agricultural products and by-products available for feeding fish. • There are suitable soils, unpolluted water and in general favourable environment that can be used for fish farming. • Recently the Regional Government has planned building of fish hatchery centre to produce fingerlings for fish farmers and reservoirs. • Aquaculture has now been included in the Federal and Regional Education Service Curriculum for Agricultural University students. It is also taught as a course in Agricultural Technical, Vocational and Educational Training (TVET) that train Agricultural Development Agents (DA). In line with this, fish farming practical training is provided for farmers in Farmers Training Centres (FTC). • Fish price is becoming attractive in the region and potential for export market to Sudan is encouraging. Challenges • The pond fish farming industry has faced many challenges to be economically and socially sustainable. • Scarcity of fish fry and fingerlings to satisfy the increasing demand. • Absence of harmonized methodologies of pond fish farming (Pond construction system, timely fish harvesting). The industry will require trained and experienced staff to successfully address these issues and to meet anticipated future growth. • The high turnover of trained staff, thus requiring periodical training. • Absence of data recording system to analyse the performance (feed, growth rate, production, etc.). Pond fish farming can be a more assured option of increasing local fish production in the region compared to management of wild stocks from capture fisheries of the lakes. However inputs made by the government and other development partners over the past years have not yielded much impact on the status and contribution of fish farming to fish availability in the region.
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Conclusion This paper concludes that there is an urgent need for establishment of fish hatchery at the central part of the region and the formulation of a separate institutional structure to look into aquaculture development in Amhara National Regional State with the help of the Regional Bureau of Agriculture and Rural development, Ministry of Agriculture and Rural Development, and all the stakeholders so as to help improve and expand fish farming development if quantitative progress is to be achieved.
Recommendations • The transfer of pond fish farming technology and knowledge should be promoted through pilot projects. • Foreign collaboration and assistance are necessary to develop fish farming. • Encouragement must be given to the education of consumers so that they can take fuller advantage of the nutritional benefits of the fishery products, particularly in communities where there is no tradition of fish consumption. Such training should include instructions in ways of preparing fish products. • For a newly developing pond fish farming in Amhara Region, there has to be a supply of people who have an understanding of how to operate and to support the farmers. The industry will require trained and experienced staff to successfully address and meet anticipated future growth. Therefore, there is a need to improve the existence of poor man-power problems at all levels. • There should be a Federal and Regional Government policy that can allocate a few percent of irrigable land area for fish farming. The region has 1.2 million hectares of irrigable land, of this amount, 347,125 hectares of land was used for irrigation last year (Tesfaye, personal communication).
Final Remarks Aquaculture in general, pond fish farming development in particular, in this region have a bright future in view of the potentials and opportunities mentioned earlier. It is hoped that in the future there will be significant boost in fish farming development to contribute very significantly to the economic development of the region and the country. Three priority issues are becoming very clear to our region: • Pilot projects are important to promote, transfer of pond fish farming technology and knowledge. • There is a strong need for establishing fish hatchery to solve the increasing demand of fingerlings. • We are in need of a deeper knowledge and understanding in building of hatchery system in practice.
References Amhara Bureau of Water Resource Development (2009). Water, No 2. Chalachew Aragaw (2004). Integrated Small-scale Fish Farming: A Training Manual . Bureau of Agriculture and Rural Development for Amhara Region. Egyptian International Center for Agriculture (EICA), (2006). Warm Water Fish Production . FAO (1995). Review of Fisheries and Aquaculture: Ethiopia . FAO Fisheries Circular No. 890 FIPP/C890 Malawi (Domasi) National Aquaculture Centre (2004). Fish farming training manual (July 26-August 7/2004).
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Fish post-harvest losses and intervention measures to reduce the losses in Koka Reservoir.
Yared Tigabu, National Fishery and Resources Research Center, PO.Box 64, Sebeta.
ABSTRACT : Post-harvest losses in fisheries include material losses of fish due to spoilage, breakage, size, discarding by catch and operational losses. Although the extent of problem varies from place to place, the country as a whole loses huge quantities of fish after capture before it reaches to consumers. The need for assessment is a first step towards overcoming losses and defining solutions to the existing problem. The survey was conducted to determine and measure the kinds and extent of losses and to propose the required actions to prevent post-harvest losses in Koka Reservoir. The loss assessment was carried out by adopting the methodology by Wood (1985) by measuring flow of fish through the system. Direct weight measurement of the catch was done with a simple balance at landing site. The total catch of the fish by species and the total discarded (due to spoilage, size, lack of market, etc) was measured. The appearance, texture and odour of the fish were assessed according to Howgate (1994). The study was conducted between September 2007 and August 2008. From estimated 210 ton total tilapia catch (in this context tilapia refers to Oreochromis niloticus and zilli species) the post-harvest loss constitute 23.5 tons (11.19 %). From estimated 187 tons of catfish (Clarias gariepinus) catch, the post-harvest losses were 30.4 tons (16.26%). Out of the total estimated 3.5 tons of common carp (Cyprinus carpio) catch, only 4.6 tons (6.6%) was discarded due to spoilage. The main reasons for post-harvest losses were the fishing method, inadequate handling facilities and delay between catch, collection and distribution, absence of regulations governing quality and standards of fish to be sold for human consumption, lack of regular supervision from the government side and poor extension service and fragmentation of duties and responsibilities in different institutions. Appropriate measures should be taken to ensure the right of consumers to safe, wholesome and unadulterated fish and fishery products.
Key words/phrases : Carp, Catfish, Fishing gears, Koka reservoir, Post-harvest losses, Spoilage, tilapia.
Introduction Post-harvest losses in fisheries include material losses of fish due to spoilage, breakage, size, discarding by catch and operational losses. There are also losses of value, what the fish is worth in monetary terms, losses of quality, when stale fish becomes less attractive to consumers, losses in nutritional value, when the fish contribute less towards the diet of consumers than it did (Geoftrey, 1990). A recent estimate of total world post-harvest loss is between 17.9 and 39.5 million ton (average 27 mil) per year (Alverson et.al ., 1994), this means in average about 30% of the total world catches. Losses in African countries are as much as 40% of the annual catch (FAO, 1989). Losses occur as a result of flaws in the handling, storage, distribution and processing of fish and in marketing techniques. The study of losses should be done on a case by case basis, and is a key step for improvement (Alverson et.al ., 1994). The important issue is how to reduce them to make more food available and, to raise income of the fishing communities. A recent study in Lake Ziway shows that there are significant post-harvest losses in the country due to different reasons. The present rate of exploitation ranged 30 to 40% of the over all potential (LFDP, 1996), there is a room for expansion, but in major rift valley lakes like Ziway, Hawassa and Chamo there is a sign of over- exploitation. The only way to develop fishery in those areas is by proper utilization of the catch. There is no room for further expansion of fishery, but by reducing post-harvest losses at all stages of fish handling, we can increase the amount of fish which reach to consumers. The need for assessment is a first step towards over-coming losses and defining solutions to the existing problem. The final stage is to describe means of reducing losses. We must know what kind of losses occur, and when, if we are to understand what processing systems need to be improved and in what respect careful studies of losses could indicate where improvements are most needed and what should be changed. The code of conduct Article II (FAO, 1998) stated that member states should adopt appropriate measures to ensure the right of consumers to safe, wholesome and unadulterated fish and fishery products. The findings of this study can be used as the base for formulation of quality assurance system in the country.
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Lake specific studies are needed to provide more precise information on the losses during the various stages of fish production (capture to marketing). The information could help to reduce post-harvest losses while increasing fish (protein) consumption without increasing the catch. The main objective of this study was to identify and measure the kinds and extent of losses and to propose the required actions to prevent them.
Materials and methods The study area: Koka Reservoir is situated in East Showa zone, Oromia region 90 km from Addis Ababa. It was constructed for hydroelectric power generation. The reservoir is located 1590 m.a.s.l and has an area of 255 km 2. It has a maximum depth of 42 m and a mean depth of 9 m. The maximum length and width of the reservoir is 20 and 15 km, respectively. The conductivity of the water is relatively low compared to other rift valley lakes (about 200 µS/cm). The water is turbid with secchi disk readings ranging between 12 and 16 cm. The loss assessment was carried out adopting the methodology by Wood (1985) by measuring flow of fish through the system (assessment format was developed). Direct weight measurement of the catch was performed quickly with a simple balance at landing site. The total catch of the fish by species and the total discarded amount of fish was measured. The appearance, texture and odour of the fish was assessed according to Howgate’s (1994) sensory evaluation of fish freshness. From the discarded fish due to spoilage, signss of spoilage, off odours, slime formation, gas formation, discoloration and change of texture was assessed visually according to Huss’ (1994) sensory method to identify cause of spoilage. From processed product (gutted and filleted), the obtained yield was measured at the landing site. The data collection sites were Denbela, Tannery, Algworash, Bridge, Tere and Gefersa. Data were collected twice a week from representative landing sites. The study was conducted between September 2007 and August 2008.
Total monthly catch was calculated using the formula:
Sum of sampling day catch X monthly fishing days Number of sampling days Monthly discard was determined by:
Sum of sample days discard X Monthly fishing days Number of sampling days Percent spoilage was calculated as: Total weight of spoilage X 100 Total weight of catch The operational yield was determined by:
Whole weight of fish-operational discard
Other information on the overall fishery activity was obtained through observation and discussion with fishermen, traders and fishery experts.
Results and discussions The fishing activity is largely concentrated on the western shore of the reservoir. The eastern shore is difficult to access. The commercially important fish species were Oreochromis niloticus and zilli (Tilapia), Clarias gariepinus (Cat fish), Cyprinus carpio (Common carp). The fishermen use beach seine, long line and gill nets. From estimated 210 tons of tilapia catch (in this context tilapia refers to Oreochromis niloticus and zilli species) within 12 months, the total post-harvest loss constitute 23.5 tons 70 Ma nagement of shallow water bodies ..., EFASA 2010
(11.19%). From estimated 187 tons of catfish ( Clarias gariepinus ) catch, the post-harvest losses were 30.4 tons (16.26%). Out of the total estimated 70 tons of common carp ( Cyprinus carpio ) catch, only 3.5 tons (5 %) was discarded due to spoilage. Beach seine and gill net are used to catch all fish species while long line is used to catch only catfish. The beach seines used in Koka reservoir are different from Lake Ziway and Langano. The wings have a length of up to 120 meters each, stretched mesh sizes 9 cm. and a height of around 2.5 meters. The sack (cod end) is up to 5 m. long and has a mesh size around 7.5 cm. The net is produced locally from imported white nylon twine with a standard twine size of 210/12 and 210/15. The permitted mesh size of the gear is 8 cm. The existing gillnet which is made up of 210/1 and 210/2 twine size and small size hook (shank length less than 30 cm) on long line are not appropriate gear for catfish harvesting. As the fish caught by these gears, the fish kicks or tramples and decompose easily, due to depletion of glycogen. Less glycogen means less lactic acid production and hence short life of fish (Huss, 1994) Immediately after the catch, a complicated series of chemical and bacterial changes begin to take place within the fish. If these changes are not controlled, the fish quickly become spoiled due to bacterial contamination and autolysis (Huss, 1994). The main reasons for spoilage in the area areinadequate handling facilities and delay between catch collection and distribution. The fishermen use planked canoes for fishing activity. The fish are exposed to direct sun and wind. The hygiene of the boats was also poor. On landing sites, the fish are dumped on the ground where they are sold to buyers. At no stage in this chain is the fish protected from direct sun and wind. There is no proper fish handling and preserving facilities both on boat and landing sites. Long fishing and staying time and the time lapse between capture and arrival at landing sites is very long (an average 2-3 hours) without any efficient cold chain system. Gill net and long line fishermen come to fishing grounds in the morning to set their gears and return the following morning to collect their catch (24 hours fishing time). Beach seines are deployed in the after noon and the catches are collected and brought to the landing site in the morning. Research finding in Lake Kariba show that an average of 35% by weight of the total catch spoils due to bacterial attack and autolysis if nets are set for more than 13 hours in tropical climate without cooling (Mulambozi, 1990). There are no regulations governing quality and standards of fish to be sold for human consumption. This is evident at landing sites where the quality of fish is mixed. In extreme cases, spoiled fishes are also sold at the landing sites. Otherwise the amount of spoiled fish could have been greater than that mentioned above. There is no regular supervision from the government side and the extension service (awareness creation, training, follow up, etc) is very poor. The lack of serious demand for good quality fish tends to encourage carelessness of the fishermen and processors. Quality assessment of the fish was done only organolepticaly and the trader relied on his own sensory judgment and on trust on the fishermen as there was no government inspection service body. The post-harvest loss increases as the catch increases. This is during fasting seasons where the demand for fish is high and the fishermen increase fishing effort without changing fish handling mechanisms. The ambient temperature during the main fasting season March to May is high and this also contributes for high spoilage rate.
Table 1 : Estimated total catch and post-harvest losses(tons) due to spoilage (from September 2007 to August 2008)
Tilapia Catfish Common carp Month Catch Spoilage Catch Spoilage Catch Spoilage Sept. 07 12.1 0.8 9.1 1.3 4.5 0.2 Oct. 07 10.5 0.6 8.5 1.1 4 0.1 Nov. 07 13.6 1.2 11.6 1.7 3.3 0 Dec. 07 15.2 1.1 13.1 1.6 5.1 0.2 Jan. 08 16.9 1.1 14.8 1.5 5.6 0.3 Feb. 08 22.4 1.6 20.3 1.9 7.4 0.2 Mar. 08 29.8 4.6 27.7 5.1 10.8 0.8 71 Ma nagement of shallow water bodies ..., EFASA 2010
Tilapia Catfish Common carp Month Catch Spoilage Catch Spoilage Catch Spoilage Apr. 08 35.2 5.7 34.1 6.2 10.7 1.0 May 08 6.5 0.1 4.5 0.6 2.2 0.1 Jun. 08 13.2 0.8 11.1 1.3 4.1 0.3 Jul. 08 15.1 1.2 14.1 2.1 5.2 0.2 Aug. 08 19.5 4.7 18.2 6.1 7.1 0.9 Total 210 23.5 187.1 30.5 70 4.6 % 100 11.19 30.4 16.26 100 6.6
Most of the private traders are not selective and buy small size and poor quality fish. As there is no quality control system in the fish trade, the private fish traders rely on their sensory judgment and trust on the fishermen. At the landing site, fish are processed on the ground and stones are used as processing table. The yields of each operation in FPME plant and at landing sites are different.
Table 2 : Yield by operation
Product type Landing site Yield (%) Tilapia fillet 29-33 “ gutted 78-80 Catfish fillet 40-44 Common carp gutted 82-86
The difference of the yield is because of the size of the fish, the post mortem phase of the fish and the workers’ capacity. A study on fish yield by Montaner, et al ., (1994) also showed that the yield varied according to the quality of raw material, the training of the worker, size of the fish and working material and facilities.
Conclusion Fish, being an extremely perishable foodstuff, needs careful treatment in handling and processing, both from public health aspects and improvement of the welfare of fishing communities. The main reasons for post-harvest losses are inadequate handling facilities and delay between catch, collection and distribution, absence of regulations governing quality and standards of fish to be sold for human consumption, lack of regular supervision from the government side and poor extension service and fragmentation of duties and responsibilities in different institution. Although the extent of the problem varied from place to place, the country as a whole is losing significant amount of fish annually through post-harvest losses. This is a massive economic and nutritional waste, which a country like Ethiopia already in danger of protein malnutrition could ill afford. The improvement of facilities from the point of production until it reaches the consumer is vital .
Recommendations • To improve fishing gear and method of fishing o Shortening the fishing time; o Introduce appropriate twine size and hanging ratio and hook size for catfish harvesting; o Upgrading the boat condition (shade, sanitary etc.). • Maintaining the fish at low temperature: To minimize spoilage, fish should be kept as cool as possible immediately after catching until processing starts. If the fish are chilled with ice it can keep in an edible condition for an increased period. However, if ice is not available in the area fish can be kept cool by other means, including the following. o Keeping the fish in the shade out of direct sun. 72 Ma nagement of shallow water bodies ..., EFASA 2010
o Placing damp sacking over the fish. This helps to reduce the temperature as the water evaporates. The sacking must be kept wet and the fish must be well ventilated. o Mixing the fish with wet grass, leaves or wet weeds, so that the water can evaporate and cool the fish. • Maintaining a hygienic environment o Keep the fish as clean as possible and avoid damaging fish by careless handling; o Keep all tools (gear, boat etc.) clean; o Keep the fish in containers and off the ground, filleting and gutting must be carried out on table; o Clean the fish working area regularly and prevent fish offal from being in contact with clean fish. • Start applying quality control practice in fishery sector by adopting regulations governing quality and standards of fish to be sold to consumers. The concept of quality and quality assurance is poorly understood among fishermen, traders and consumers. • Introduce proper fish utilization, preservation and processing techniques and start effective training program for fishermen and traders on proper fish handling, processing and storing techniques. The training should be carried out in a steady pace and in a repetitive manner. • Make compatible duties and responsibilities of different institutions. The reduction of post-harvest losses through improved handling and processing, transport and distribution system should be given high priority, as it will make an important contribution to the improvement of the fishery sector
References Alverson, D.L., Freeberg, M.H., Pope, J.G., Muravaski, S.A., (1994). A global assessment of fisheries by-catch and discards. FAO Fish. Tech. pap ., (339):233. FAO (1989). Fish technology in Africa. FAO Regional Cooperative research in Africa. Rome. FAO (1998). Responsible fish utilization. Technical Guidelines for Responsible Fisheries. No.7 Rome. Geoffrey, R. (1990). The kinds and levels of post-harvest losses in African inland fisheries. In: proceeding of the symposium on post-harvest fish technology. CIFA Technical paper No 19. Rome, FAO. 1992 (1-9). Howgate, P. (1994). Proposed draft Guideline for the Sensory Evaluation of Fish and Shellfish. Cx/FF9 (ital.) 94/0. Joint FAO/WHO food standards programme. Huss H.H. (1994). Assurance of sea food quality. FAO fisheries technical paper No. 334. LFDP (Lake Fisheries Development Project) final report May (1996) Addis Ababa, Ethiopia. Montaner, M.I., Parin,M.A., Zugarramudi, A.Y Lupin,H.M.,(1994a) Requerimiento insumos en industria pesquera. Alim., (Espana), (253):19-24 Mulambozi (1990). Post-harvest fish technology in Zambia. In: Proceedings of the symposium on post-harvest fish technology. Cairo p.103-106. Van den Bosche, and J.P. Bernacsek (1991). Source Book for the Inland Fishery of Africa . CIFA Technical paper No. 318.3. FAO, Rome. Wood, C.D. (1985). A methodology for the assessment of losses of cured fish and evaluation of countermeasures. In: Proceedings of the FAO expert consultation on fish technology in Africa, Lusaka, P.360-368
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Comparative growth performance in pond culture of four Nile tilapia (Oreochromis niloticus) strains collected from different Ethiopian freshwater lakes
Kassaye Balkew Workagegn and Gjoen Hans
ABSTRACT: This study was conducted in National Fishery and Other Aquatic Resources Research Centre, Ethiopia, to compare the growth performance of four juvenile of Nile tilapia (Oreochromis niloticus) strains in pond culture. A mixed-sex of juvenile Nile tilapia strains were collected from four Ethiopian Lakes by using beach sieve mesh. They were transported to the research centre using polyethylene bags. The fish of length from 8cm to 10cm weighing 10g to 15g were selected as experimental fish from each of the strains. Each strain was stocked in triplicates in 5m x 5m x1.5m pond size at a stocking density of 2fish per m -2. The average water temperature of the pond during the experiment was 20.4 oC.The fish were fed 3% of their body weight per day manually twice a day with locally available feed which composed of 23% crude protein for 60 days. The result showed that the Koka strain had significantly (p<0.05) higher final mean body weight, specific growth rate and gross fish yield than the Ziway and the Hora strains. But, it was not significantly (p>0.05) different from the HaHawassa strain. The HaHawassa strain had significantly higher final mean body weight and specific growth rate than the Ziway strain, but not significantly different from the Hora strain. Similarly, the Koka and the Hawassa strains had significantly higher daily growth rate than the Ziway strain, but not significantly different from the Hora strain. The Hora strain had slightly higher specific and daily growth rates than the Ziway strain, but statistically there was no significant difference between them. However, at the end of the experiment, statistical analysis showed that there was no significant difference in feed conversion ratio and Fulton’s condition factor among all the strains. With the exception of the Ziway strain, all the strains revealed an isomeric growth pattern. The overall conclusion is that growth performance among strains of Oreochromis niloticus was significantly different and thus, it is crucial to select the right strain for aquaculture purpose. However, further research may still be needed to compare more strains from different Ethiopian lakes at different life stages as well as at different environmental conditions to evaluate the robustness and the genetic potential of the strains to be utilized in Oreochromis niloticus breeding program as base population in the country.
Key words/phrases: Feed conversion ratio, Growth performance, Lakes, Oreochromis niloticus Strains, Pond culture.
Introduction Global aquaculture production : The aquaculture industry has been developing very rapidly throughout the world over the last few decades. Currently, it is the fastest growing food production sector in the world with annual growth rate of 6.1% by volume and 11.0% by value (FAO, 2009a).The growth rate of aquaculture is much more rapid than all other food producing sectors, such as animal husbandry and capture fisheries (Lucas, 2003). It has increased dramatically from less than 1 million tons in 1950s to 51.7 million tons in 2006 with a value of US$ 78.8 billion. The per capita supply of aquaculture also increased from 0.7kg in 1950 to 7.8kg in 2006. The contribution of aquaculture to the total global aquatic food production has grown over the last few decades, from 3.9% of the total production (by weight) in 1970 to 36.0 % in 2006 (FAO, 2009a). Thus, aquaculture industry seems to have potential in creating a significant contribution to the world food supply. To maintain the present per capita consumption, about 40 million tons of additional seafood is expected in 2030 (FAO, 2006). Thus, the development of aquaculture production should be continuously increased especially in tropical and subtropical area where many types of aquaculture fish species are widely cultured (Gjedrem, 2005). Among several cultured fish species, tilapia is one of the most commercially important and widely used fish in the global aquaculture production. Tilapia, which belongs to family Cichlidae, originated in Africa and became distributed almost all over the world (Cnaani and Hulata, 2008). The contribution of tilapia to the global aquaculture production was very low during the early 1970s (El-Sayed, 1999); it was only 12,058 tons in 1970. However, tilapia culture has shown a huge expansion during the past decade. As a result, the production of farmed tilapia has reached to more than 2.12 million tons in 2007 (Fig.1).
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In the last two decades, the most commercially cultured species in the global tilapia farming was dominated by three species namely: Oreochromis niloticus, Oreochromis mossambicus and Oreochromis aureus (Suresh, 2003) . Of these, Oreochromis niloticus was by far the most widely cultured fish in the world tilapia production (Bentsen et al .,1998; Pillay and Kutty, 2005; El-Sayed, 2006) and accounted more than 81% of the total cultured tilapias (Suresh, 2003).
Fig.1 : Global Aquaculture Production of Oreochromis niloticus from 1950 to 2007 (Source: FAO 2009b)
Nile tilapia aquaculture with a special emphasis in Ethiopia : Ethiopia is located at the north east corner of Africa. Agriculture is the backbone of the country’s economy. It accounts for about 50% of the total Gross Domestic Production (GDP) employing more than 85% of the total population of the country (Deressa, 2007). However, the production of agriculture is limited due to climate change, reduction of soil fertilities, economical and other constraints. Hence, the production of animal proteins from the agriculture sector such as livestock products (milk and meat) may not cover the necessary animal protein requirements for the population in the country. Due to this constraint, the development of aquaculture industry can offer an alternative to increase the production of fish as one of the cheap protein source in the country. Even though Ethiopia is a landlocked country, there are lots of freshwater resources (lakes and rivers) which offer a great potential for fisheries and aquaculture development. The total area of the lakes and reservoirs are estimated to be 7000km 2, small water bodies make up about 400km 2 and the major rivers stretch over 7000km in the country (Mebrat, 1993). Most of the lakes are located in Ethiopian Rift Valley Region and are inhabited by varieties of fish species such as Tilapia spp., Catfish spp., Carp spp. and Barbus spp . (LFDP, 1998). Fish culture in Ethiopia has been practiced for many years. Extensive aquaculture started in 1975 through National Fisheries and Other Aquatic Resources Research Centre. Recently, capture fisheries and aquaculture industry have grown in different parts of the country. However, the majority of fish production is from capture fisheries. In 2001, annual fisheries potential of the major lakes, reservoirs,
75 Ma nagement of shallow water bodies ..., EFASA 2010 small bodies and major rivers was estimated to be 51,481tons (Appendix I). However, the total landing was estimated to be only 15,389 tons per year representing 30% of the estimated potential (FAO, 2003). Based on the population size of the country, the estimated annual demand in 2001 was 65,344 tons (i.e., 1kg per person). However, the estimated annual per capita of fish produced was less than 240g per person (FAO, 2003). With the existing human population growth rate, the future demand of fish is estimated to be 94,526 tons in 2015 and 117,586 tons in 2025. If other factors such as a rise in income, increase fish supply expansion of fish distribution and increase fish product quality, the demand will be projected by 15% to 20% (FAO, 2003). As a result of the overall factors including a high human population growth rate, the demand of fish in the country is increasing rapidly. Thus, the estimated demand for fish can be met only when capture fisheries is supported by aquaculture production system. Currently, Ethiopia has implemented aquaculture industry to bring rapid economic growth and development. Thus, extensive and semi-intensive rural aquaculture development for best known species such as tilapia is prioritized to achieve food security in the country. Moreover, the availability of agricultural and industrial by-products for fish feed seems promising. As a result of the overall possibility, Ethiopian government is planning to develop rural aquaculture industry as part and package of rural development strategies for more commercial important fish species such as Nile tilapia. Nile tilapia is one of the most commercially important fish for both fisheries and aquaculture production in the country for several reasons. These include: • Biological reasons: fast growth and ability to utilized wide varieties of cheap feeds (feeding habits) and good reproduction potential (easy to breed in the farm); • Physiological reasons: adopt a wide range of environmental conditions; • Social reasons: good table-food with relatively lower market price (Abdel-Tawwab, 2004; Ashagrie et al ., 2008). Besides, Nile tilapia is relatively easy to improve the genetic potential through selection and breeding from the existing and wild fish brood stocks (Ridha, 2006). Feeding and management practice : In intensive aquaculture system, the cost of formulated feed is a major component of operating cost in fish farms. It accounts more than 50% of the total expenses (Ridha, 2006).This high operation cost is mostly related to the protein quality of the feed. As a result, improving feed conversion ratio of the cultured fish would have a positive impact in reducing the production cost. As mentioned above, Ethiopian aquaculture was started in 1975, but it is still in small- scale extensive farming system (FAO, 2003). The main feed source in this system is mostly natural feeds such as planktons, small invertebrates, vegetable debris and benthic organisms (Trewaves, 1982; Getachew and Fernando, 1989; Suresh, 2003). To increase the productivity of this culture system, artificial fertilizers or natural manures can be added. Besides, supplementary feed is used for semi- intensive culture system. Nile tilapia is a successful candidate to such type of culture systems. This is because Nile tilapia is considered as macrophytophagous, microphagous and omnivorous in its feeding habits (Pillay and Kutty, 2005). Since Nile tilapia is at a lower trophic level in its feeding habit, it has an ability to transfer energy from lower food chain to the higher energy level. Moreover, it has flexible feeding habit and has the ability to use more diversified feed resources. Nile tilapia can shift from plant feed components (vegetable debris, phytoplankton and algae) to animal feed components (zooplankton, insects, mollusks, etc) depending on the availability of animal feed components in the system (Spataru and Zorn, 1978). The feeding regime of Nile tilapia depends on the availability of feed in the natural condition. The feeding habit and dietary preference of Nile tilapia is also related to the life stage of the fish (El-Sayed, 2006).Tilapia larvae feed on zooplankton, juveniles of Nile tilapia feed on phytoplankton and zooplankton and adult Nile tilapias feed on small invertebrates (Tudorancea and Harrison, 1988; Suresh, 2003). However, the requirement of nutrients for Nile tilapia depends on different factors. These factors include life stage, dietary energy content, dietary protein sources, water quality and culturing conditions. For instance, protein requirement for maximum growth performance of larval stage of Nile tilapia, juvenile and adult Nile tilapia ranges from 35-50%, 30-40% and 20-30% of the total component of the feed, respectively (El-Sayed and Teshima, 1992). Therefore, the requirement of ten amino acids and protein for maximum growth depend on the quality of feed and size of the fish (Getachew and Fernando, 1989). In Ethiopia, however, due to the lack of well formulated feed, fish diet preparation depends on locally available feed ingredients. Thus, the proximate feed compositions used by local fish 76 Ma nagement of shallow water bodies ..., EFASA 2010 farmers vary depending on the availability of feed ingredients. The most widely use feed ingredients include mill sweeps of different cereal crops such as wheat, maize and sorghum. Families, species and subspecies (strains) : Tilapias represent a large number of freshwater fish species within the family Cichlidae. Based on meristic, morphomotric, ethological characteristics and genetic variation, tilapias are grouped into three genera namely: Oreochromis, Tilapia, and Sarotherodon. Genera Oreochromis and Sarotherodon are mouth brooders (Laurent and Jean-François, 1995). Genus Oreochromis is maternal mouth brooder while genus Sarotherodon is paternal or biparental mouth brooder. Genus Tilapia is not a mouth brooder rather it is substrate spawner (Suresh, 2003). There are also variations within a species due to geographical differences. The wide geographical differences between different population of Oreochromis niloticus leads to a significant genetic divergence, resulting in distinct subspecies and strains. For instance, there are variations in growth performance between four African strains and four Asian strains reared in different environmental conditions (Eknath et al., 1993; Bentsen et al., 1998). As reported by Eknath et al., (1993), African strains grew better than Asian strains with the exception of Ghanaian strain reared in different environmental conditions. Breeding characteristics of Nile tilapia in both wild and aquaculture : Nile tilapia usually needs shallow, muddy and sandy bottom areas for breeding. In these environments, sexually matured male creates a territory and builds a nest. Sexually matured female lays her eggs on the nest and then the male Nile tilapia releases its milt on the eggs for fertilization. After fertilization the female collects the eggs and incubates them in her mouth. The eggs stay in her mouth for about 6-10 days until hatching (Nandlal and Pickering, 2004). Sexual maturation of Nile tilapia varies depending on several environmental factors such as temperature, feed availability and genetic variation. Most of the time, first sexual maturation occurs within a range of 4 to 6 months (Suresh, 2003). Sometimes age at first sexual maturation occurs within a range of 2 to 4 months at body weight of 30 to 50g (Galemoni de Graaf and Huisman, 1999). Once Nile tilapia sexually matures, it produces offspring throughout the year if the water temperature stays above 20 0C (Trewaves, 1982). Temperature range from 25 0C to 30 0C provides an ideal condition for Nile tilapia spawning (Nandlal and Pickering, 2004). Age at first sexual maturation is relatively earlier in small water bodies than large water bodies (Kolding, 1993). In addition, age at first sexual maturation of Nile tilapia is affected by water quality (Jones and Reynolds, 1997). Under aquaculture condition, age and size at first sexual maturation for Nile tilapia seems smaller than that of the natural condition (El- Sayed, 2006). In general, age and size differences at first sexual maturation and spawning frequency depend on different environmental factors such as food availability and temperature (Trewaves, 1982, Trewaves, 1983) and geographical structure (Kolding, 1993) and genetic factors (Duponchelle and Panfili, 1998). Environmental requirements : Nile Tilapia can be cultured under extensive, semi-intensive and intensive pond culture systems. Some of the main environmental factors in Nile tilapia pond culture are temperature, dissolved oxygen, pH, salinity, carbon dioxide, nitrogenous waste substances such as ammonia and nitrate. These water quality parameters affect the growth performance of the fish in pond culture. Temperature : The the main environmental factors that affect the growth of cultured fish. Change in water temperature will have an effect on growth, metabolism, reproduction, feed consumption, physiology and survival of Nile tilapia. The optimum temperature required for maximum growth of Nile tilapia ranges from 28 0C to 30 0C (Beamish, 1970). But it can tolerate a wide range of temperature from 80C to 42 0C (Philippart and Ruwet, 1982; Trewaves, 1983; FAO, 2009b). However, temperature for normal Nile tilapia growth and reproduction ranges from 20 0C to 35 0C (Trewaves, 1983). At optimum temperature, the body processes stay moderate. When temperature increases, the body processes will be faster. But the processes collapses when the temperature increases above 42 0C (FAO, 2009b). In contrast, when temperature reduces below 16 0C, these processes go slower. If the temperature declines below 10 0C, mortality of fish increases (Sifa, et al . 2002; Azaza et al . 2008). At higher temperature, tilapia becomes very sensitive to low oxygen concentration and high ionic concentration and leads to high mortality. However, there is genetic variation between Nile tilapia strains in response to temperature differences (El-Sayed, 2006). Variation in response to temperature is also observed at different life stage and size of fish (Charo-Karisa et al ., 2005).
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Dissolved Oxygen (DO): The availability of ambient DO is important for normal growth and metabolism. Mostly Nile tilapia can tolerate at low dissolved oxygen levels; but the growth rate is very sensitive for other factors if dissolved oxygen concentration is below 1.0 mg l -1 (Yi, 1998). Low dissolved oxygen concentration causes reduction of metabolism, feed intake, digestion efficiency and growth of fish. In contrast, high dissolved oxygen concentration is toxic to the fish. Optimum DO concentration is important for normal growth of Nile tilapia. DO demand of Nile tilapia varies depending on water temperature, feeding condition as well as size of the fish. For instance, the smaller the fish size the higher the dissolved oxygen demand and vice versa (Franklin et al., 1995). Franklin et al . (1995) also reported that at higher temperature, the demand of dissolved oxygen is higher. DO content in water is affected by several factors such as rate of photosynthesis, respiration and decomposition. Thus, during day time dissolved oxygen concentration becomes high due to photosynthesis. In contrast, during night time dissolved oxygen concentration becomes low due to high respiration and decomposition. If there is a low dissolved oxygen concentration, anaerobic decomposition of sediment forms toxic substances such as H 2S that causes reduction of fish growth and damage to fish gills (Pillay and Kutty, 2005). Carbondioxide, pH and Alkalinity: Acidity, alkalinity and pH are also the main factors that affect the growth of Nile tilapia. These factors are highly inter-related to each other. Depending on the rate of decomposition, concentration of carbondioxide will change. An increase in carbondioxide concentration leads to decrease in pH level. The fluctuation of pH is also dependent on the alkalinity of the water. Alkalinity is the capacity of water to accept H + ions or the pH buffering capacity of water maintaining it to resist change in its pH value. Buffering capacity of seawater is relatively high due to the presence of carbonate system. In contrast, the buffering capacity of fresh water is relatively low as result of low carbonate system, thus photosynthesis and respiration have drastic effect in pH change. The concentration of free carbondioxide, bicarbonate and carbonate in the carbonate system is affected by pH value of the water. If the pH value is less than 4, the concentration of carbon dioxide is high and it becomes toxic to the fish. When pH is around 7.5, bicarbonate become dominant, however, carbonate becomes dominant if pH is greater than 7.5 (Poxton, 2003). Nitrogen wastes (ammonia, nitrite and nitrate) : Nitrogen is the end product of metabolic protein breakdown in fish and other organisms. Nile tilapia excretes nitrogenous waste substances mainly through its gills. These waste substances include ammonia, small amount of urea and uric acid. Ammonia is very toxic and is the most critical nitrogenous waste substances in fish culture. The toxicity level of ammonia depends on pH, carbondioxide and dissolved oxygen. Cherviski (1982) reported that the toxicity of NH 3 increases with decreasing pH and dissolved oxygen concentration, and decreases with increasing carbon dioxide. Ammonia toxicity causes reduction in salt regulation of kidney and reduces oxygen content in the blood (El-Sayed, 2006). Thus, the concentration of NH 3 should be maintained below 0.1mgl -1 to achieve a normal growth performance of the fish (El-Shafai et al ., 2004). - In natural system, nitrifying bacteria have a capacity to oxidize NH 3 to nitrite (NO 2 ) and then to nitrate - (NO 3 ) which is relatively non-toxic for Nile tilapia (El-Sayed, 2006). Thus, the concentration of NH 3 can be reduced by nitrifying bacteria found in the suspended organic substances of the pond or other Nile tilapia culturing systems. In general, water quality parameters such as physical properties (temperature, suspended solid particles, turgidities), chemical properties (pH, DO, NH 3, alkalinity, salinity) and biological properties (density of macroorganisms and microorganisms) are the most important factors that affect the growth performance and feed consumption of farmed fish and thus should be considered during Nile tilapia culture. Stocking density : Several investigators have reported that tilapia can tolerate high stocking density; and they withstand extreme crowding conditions in pond culture. Hence, pond culture is the most widely used method for tilapia production. Nile tilapia is a successful candidate in pond culture. Its success is due to the fact that Nile tilapia has a capacity to use natural feed source found in the pond. The stocking density is the main important factors affecting intensive fish culture. The relationship between stocking density and Nile tilapia growth is the function of a number of biological and physiological factors such as life stages, size, sex, social hierarchies and their tolerance to the environmental change (El-Sayed, 2006). For instance, the growth performance of Oreochromis niloticus
78 Ma nagement of shallow water bodies ..., EFASA 2010 fry decreased with increasing stocking density from 3 to 20 fry per litters. This leads to social stress and chronic stress, which causes reduction in growth performance of the fish (El-Sayed, 2006). Environmental concern with genetic flow between wild and cultured strains : The rapid growth of aquaculture industry may cause negative environmental impacts. These may include ecological or genetic or both of the local ecosystems. The negative impact of aquaculture to the surrounding environment may be due to poor farming designs and management system, which include planning, site selection, feed management and escapees of farmed fish. The Ecological and the genetic impacts are mainly caused by organic pollutant, pathogenic organisms, and movement of seed stocks and disturbance of foreign species on local stocks. There is a direct or an indirect genetic impact on local stock from escapees. The main problems related to escapees, transferring and introducing fish are breeding with wild stocks, disease transfer, and competition for feed, space and habitat modification (Cripps and Kumar, 2003). Nile tilapia is known to adapt to wide range of habitats and can even adapt to a new habitat and reproduce successfully. Nile tilapia, as alien species, has a capacity to invade and exist under natural conditions and then make unsuitable environmental condition for the local species. For instance, the introduction of tilapia to India caused a decrease yield of native fish species such as Indian carp and mirror carp in many reservoirs (Natarajan and Aravindan, 2002 cited in El-Sayed 2006). Late niloticus and Oreochromis niloticus were introduced in Lake Victoria in the1950s and early 1960s. They dominated over the native fish species in the lake during 1980s; thus many endemic fish spaces were eliminated, and later the biodiversity of the lake was changed (Ogutu-Ohwayo and Hecky, 1991). In addition to the effect of escapees, organic pollutant and waste substance from the fish farm may affect the biodiversity of the receiving ecosystem by altering the bottom environmental conditions for bottom resident organisms (Brooks et al ., 2003). Environmental effect from this sector is not noticed in Ethiopia since aquaculture industry is at infant stage. But collecting, transporting, introducing of fry to different parts of the country for different purposes such as research activities and disseminating of fry to the local fish farmers may cause different impacts to different aquatic ecosystems and may cause changes in biodiversity. In addition, there are overfishing activities in different lakes and other water bodies in the country. There are some regulations related to conservation of genetic materials of wild fish population to avoid mixing of different populations found in different water bodies (lakes and rivers). Such regulations include restriction of mobility of life fish, prohibition of distractive gears, small mesh size, allocation of catch, seasonal closures (FAO, 2003). Growth performance and feed conversion ratio : Growth is a complex biological process affected by several factors such as physiological, behavioural, nutritional, genetic and environmental. It is defined as change in magnitudes.The change can be in size (length or weight or both) and body compositions. It is the process of deposition of nutrient in the body. The genetic factor (indigenous factor) of the target fish, providing sufficient amount of balanced diets and optimum environmental conditions (exogenous factors) are important to achieve maximum growth of the cultured fish (Oldham et al., 1997). Nile tilapia culture requires a well formulated feed to meet protein requirements (Halver and Hardy, 2002) and selection of genetically improved strain (Eknath et al ., 1993). Identification of relatively fast growing strains in their early life stage is an important aspect in aquaculture to enhance the genetic potential of the fish (Abdel-Tawwab, 2004). Thus, the first step of selection is characterising the available strains and subsequently select one or more strains to form a base population for genetic improvement (Lutz, 2006), and thus an increasing in productivity through the application of genetic techniques (Shepherd et al ., 2006). Therefore, determination of genetic variation on the growth performance of different O. niloticus strains is very important for breeding program. The expected genetic differences between groups of fish has been widely used for efficient selection of the optimum strain that could be utilized for the improvement of fish culture and breeding program (Bolivar et al ., 1993; Eknath et al ., 1993; Palada-de Vera and Eknath, 1993). Moreover, Eknath et al ., (1993) reported that the analysis of the performance of the strains across environments led to the conclusion that the relative importance of genotype-environmental interaction was low compared to that of the strain difference. They attributed this difference to strain specific effect on growth performance.
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Research on Oreochromis niloticus which focused on genetic improvement and selective breeding programmes have led to the development of a number of improved strains for low-cost sustainable aquaculture that exhibited superior growth performance over the existing stocks’ (Ridha, 2006). For instance, Genetically Improved Farmed Tilapia (GIFT) had a cumulative increase of 85% in growth rate, delayed sexual maturity and is more resistant to cold temperature compared to the base population (El- Sayed, 2006). The author also reported that GenoMar Supreme Tilapia (GST) strain had 80% survival rate and less than 1.10 feed conversion ratio on average which is much better than its base population. In fish farming practice, growth performance of cultured fish is an important consideration in pond and other culture systems to increase the production of the farmed fish. However, in Ethiopia there are no data to compare growth performance of different strains of Oreochromis niloticus in pond culture. Therefore, this study is the first attempt to provide data to compare the growth performance of different strains of this tilapia species in pond culture. Feed conversion ratio (FCR): This is one of the most important economical traits in genetic improvement and selective breeding programmes (Quinton et al ., 2007). Mostly, it can be measured using genetic correlation with growth trait of the fish (Gjedrem, 2000). The genetic correlation between FCR and growth rate is relatively high for many fish species. As reported by Gjedrem (2000), the genetic correlation between FCR and growth rate for many fish is ranging from -0.80 to -0.95. FCR is a ratio of feed intake in gram and weight gained of the fish in gram. The smaller FCR indicates improved feed consumption efficiency of the fish. In addition to genetic effect, the value of FCR may be affected by different factors such as feeding rate and quality of the feed. As reported by Bardach et al . (1972), feeding rate can affect feed conversion ratio and growth rate of juvenile of Java tilapia. The fish were fed the same types of feed with different feeding rate (1%, 2%, 3% and 4% of their body weight). The result revealed that the fish fed at 3% feeding rate of their body weight grew best. In this case, feed conversion ratio was moderate as compared to other feeding rates. FCR was best for the fish fed at 2% and 1% feeding rates, respectively, but the growth rate was relatively low. On the other hand, FCR was relatively higher for the fish that fed at 4% feeding rate and resulted in moderate growth rate of the fish. Length-weight relationship (LWR) and Fulton’s conditional factor : It is believed that LWR is a good indicator for the general “well being” of the fish population in a given environmental conditions. This relationship is an important parameter to characterize the growth pattern and growth performance of the fish in different fish culture systems (Bolger and Connolly, 1989; Costa and Araújo, 2003). Based on this relationship, the growth pattern of the fish can be determined. The growth pattern of the fish may be termed as isometric if the LWR growth exponent ‘b’ in length-weight equation W= aL b is three (Olurin and Aderibigbe, 2006). In this case, change in length and change in weight of the fish are proportional. When the LWR growth exponent is greater or less than three, change in length and change in weight of the fish is not proportional, indicating allomeric growth pattern. If the value of LWR growth exponent is less than three, thus the fish became thinner on account to its growth in length. On the other hand, if the value of LWR growth exponent is greater than three, indicating that the fish become heavier because of the weight increase (Halver and Hardy, 2002; Ariyaratne, 2004). Fulton’s condition factor is the ratio of mean body weight and mean body length of the fish. It is affected by several environmental factors such as seasonal variation, types of feed and age of the fish (Bakhoum, 1994; Khallaf et al ., 2003). Thus, Fulton’s condition factor is very important to study fishery biology (Medri et al ., 2000). In general, LWR and Fulton’s condition factor indicate the wellbeing of fish. In addition, LWR is important in aquaculture to estimate fish biomass from underwater length observation (Yi, 1998). The condition factor is very important in studies of fishery biology and indicates the wellbeing of the fish in the environment they live to verify if good use of the ration (Medri et al ., 2000). Thus, LWR is an important indicator about the condition of the fish which in turn tells us about the environmental and genetic factors that are responsible for growth. Several investigators have studied on feed and feeding habit of Nile tilapia strains in their natural habitat in different Ethiopian lakes (Getachew and Fernando, 1989; Dadebo, 2000; Fetahi and Mengistou, 2007; Alemayehu Abiye, 2008), on effect of stock density on growth performance in cage culture (Ashagrie et al ., 2008), on growth performance of Nile tilapia on different lakes based on otolith analysis (Admassu and Casselman, 2000) and on growth performance Nile tilapia in pond culture at differ stocking density
80 Ma nagement of shallow water bodies ..., EFASA 2010 using poultry loading (Alemu, 2003). However, there are no research reports on the growth performance of different Nile tilapia strains in pond culture. Hence, comparative data are not available on the growth performance and feed utilization on different Nile tilapia strains in Ethiopia. The general objective of this study was therefore to compare the growth performance of four Nile tilapia ( Oreochromis niloticus ) strains collected from four Ethiopian fresh water lakes (Lakes Hawassa, Ziway, Koka and Hora) in pond culture to enhance the production of tilapia aquaculture in the country. Different growth parameters were used to compare the growth performance of different Nile tilapia strains. The specific objectives of this study were: • To estimate the specific growth and survival rates of the strains in pond culture, • To determine the feed conversion rate and gross fish yield of the strains, • To evaluate the growth pattern (growth condition) of the strains, and • To identify strains with better growth performance in pond culture.
Materials and methods Description of the study sites : The experiment was conducted in National Fishery and Other Aquatic Resources Research Centre (NFARRC), Ethiopia. The research centre is situated to southwest direction of Addis Ababa, the capital city of Ethiopia at a distance of 24km. The climatic zone is classified as mid-altitude zone (2240m above sea level). The mean annual minimum and maximum temperature of the area is 15 oC and 21 0C, respectively with an average annual rainfall of 890mm (Ashenafi and Eshetu, 2004). The research centre was constructed in 1975 on a total area of two hectares. It consists of one laboratory and hatchery. It has outdoor ponds made of 18 units (Fig. 2). These ponds are used for research purpose as well as for stocking of fingerlings until dissemination to the local fish farmers. The propagated fish in the research centre are Tilapia spp. (Oreochromis niloticus, and Oreochromis zilli ), Clariasis garpeinus and Goldfish.
Fig. 2 : The study site (NFARRC) with the hatchery and outdoor ponds
Ethiopia has many natural fresh water lakes and rivers. Some of them are found in the highland areas of the country. Most of the lakes are found in the lowland area of the country. Eight of them (Lakes Hawassa, Chamo, Chew Bahir, Langano Shalla, Ziway, Abaya and Abiyata) form a chain of lakes in the Ethiopian rift valley (Fig. 3). These lakes cover about 40% of the total area of the lakes in the country. There are also some artificial lakes in Ethiopia such as Lake Koka and Finacha (Fig. 2.2). Most of these water bodies are inhibited by different commercially important fish species such as Tilapia spp., Catfish spp. and Barbus spp . (LFDP, 1998). Of several Ethiopian lakes, Lake Hawassa, Lake Ziway, Lake Koka and Lake Hora are some of the most widely used rift valley lakes for fisheries and thus they were selected as a source of Juvenile of Nile tilapia fish for this study.
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Nile tilapia is the most widely distributed fish species inhabiting a diverse ecosystems ranging from lowland to highland fresh water bodies found in the country. It is found in all rivers, lakes and reservoirs within a temperature that ranges from 8 0C to 42 0C (Trewaves, 1983). It is also found in muddy and sandy shallow water habitats where natural feeds are abundant. The distribution of tilapia depends on physiological, behavioural, and biological adaptations to different environmental condition (Caulton and Hill, 1973), feed preference (Philippart and Ruwet, 1982) as well as prey and predators found in the ecosystem (Pet et al ., 1996). Thus, understanding of the distribution and habitat of tilapia is important for both genetic and environmental management systems (Pet et al ., 1996).
1= L. Abaya, 12=L. Hora, 2=L.Chaw Bahir, 13=L.Babigata, 3= Lake Tana, 14= L. Aresade 4= Lake Ziway, 15=L. Rudolf, 5=L. Langano, 16=L. Ashange, 6=L.Hora Abiata, 17=L. Besheftu, 7=L. Shalla, 18= L. Koka 8=L. Awassa (reservoir), 9=L. Chamo, 19=L. Guwane, 10=L. Fincha 20=L. Abe, (reservoir), 21=L. Gargori 11=L.Haik,
(Source FAO, (1991) and Balarin( 1986)).
Fig. 3 : Distribution of the most important Ethiopian highland and lowland lakes (the numbers indicate the location of the lakes and the arrows indicate sampled lakes).
Lake Hawassa is found in the Ethiopian Rift Valley Region. It is located 275km south of Addis Ababa at an altitude of 1680m above sea level. The surface area of the lake is 90km 2 with a maximum and mean depth of 23m and 11.6m, respectively (Kebede et al ., 1994). The authors also reported that the mean annual minimum and maximum surface water temperature of the lake is 7.5 0C to 28.8 0C, respectively with a mean annual rainfall of 1154mm. There is one known small tributary namely Tikur Wuha River that feed the lake from the northeast direction. There is no any known outflow river from the lake. The phytoplankton are dominated by different groups of algae such as green algae, blue green algae and diatoms (Kebede and Belay, 1994). The lake is also rich with different zooplankton species and debris. Thus Lake Hawassa is classified as eutrophic lake (Fetahi and Mengistou, 2007). The dominant fish are Tilapia (Oreochromis niloticus ), African catfish ( Clariasis garpinus ), Barbus ( Barbus intermedius and 82 Ma nagement of shallow water bodies ..., EFASA 2010
Barbus Amphigramma ), Garra sp . and Applocheilichthys sp . (Fetahi and Mengistou, 2007).The first three fish species are commercially important for fisheries.
Lake Ziway is found in the northern part of the Ethiopian Rift Valley Region at an altitude of 1636m above sea level (Ayenew, 2007). It is located 160km south of Addis Ababa. The mean annual surface water temperature is 15 0C to 25 0C with a range of 600mm to 1200mm annual rainfall (Vallet-Coulomb et al ., 2001). The surface area of the lake is 442km 2 (Admassu and Casselman, 2000). The maximum and minimum depth of the lake is 9m and 2.5m, respectively. It has three tributaries: two inflow rivers (Ketar and Meki Rivers) and one outflow (Bulbula River) (Vallet-Coulomb et al ., 2001). Lake Ziway is rich in emergent macrophytes such as Phragmitest spp ., Scripus spp., Cyperus papyrus and Typha angustifollia , but they are less abundant here than in Lake Hawassa (Martens and Tudorancea, 1991). As Martens and Tudorancea (1991) reported that water lily Nymphaecae coerulea and Potamogeton spp . are some of the most commonly distributed floating and submerged macrophytes found in the lake, respectively. The most dominant fish species are Tilapia ( Oreochromis niloticus, Oreochromis zilli and Oreochromis Mozambique ), African catfish ( Clariasis garpinus ) and Crucian carp ( Caracius caracus ) (LFDP, 1998). Oreochromis niloticus is the most important fish for fisheries followed by Clariasis garpienus .
Lake Koka is an artificial lake (reservoir) which is found in the northern part of Ethiopian Rift Valley Region at an altitude of 1660m above sea level (Mesfin et al ., 1988). It is located 100km south of Addis Ababa. The surface area of the lake is 255km 2 with a maximum and mean depth of 14m and 9m, respectively (Balarin, 1986). The mean annual surface water temperature of the lake is 27.9 0C. Awash River is the main inflow and outflow river. Besides, there are other small tributaries such as Mojo River that fed the lake. The nature of the lake is similar to those of the natural lakes found in the region, but it is more turbid than other lakes such as Lake Hawassa and Lake Ziway due to high organic debris (Mesfin et al ., 1988). As reported by Mesfin et al . (1988), Lake Koka is rich in phytoplankton (Cyanophyta, Chlorophyta), zooplankton (Rotifers, Copepoda) and benthic fauna, mostly nematodes. Microsystis is the most abundant phytoplankton in this lake. The dominant fish species are Tilapia spp., Barbus spp ., Clarias spp, and Cyprinus spp. (FAO, 1991).The first three fish species are the most commercially important fish in the lake.
Lake Hora (Hora-Arsedi ) is the fourth site for collection of juvenile Oreochromis niloticus . It is found in the highland area of the country outside the Ethiopian Rift Valley Region. It is located 52 km southeast of Addis Ababa at an altitude of 1860m above sea level (Lemma, 2008). Lemma (2008) also reported that the surface area of the lake is 1km 2 with a maximum and mean depth of 35m and 17.5m, respectively. The mean annual surface water temperature of the lake is 22.7 0C. The nature of the lake is slightly saline as compared with other sampled lakes. There are no known inflow and outflow rivers. The dominant fish species in Lake Hora are Oreochromis niloticus and Oreochromis zilli . Some of the physical and chemical properties of the all the four lakes are summarised in Appendix II.
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Fig. 4 : A chain of eight Rift Valley Lakes; the arrows indicate the sampled lakes (Source: Tadesse Fetahi and Seyoum Mengistou, 2007) Collection of juvenile Oreochromis niloticus from the four lakes : Healthy juveniles of Oreochromis niloticus strains of mixed-sex were collected from four Ethiopian lakes described above by using a 50m length and 2.5m width beach sieve mesh whose stretched length was 20mm (Fig.4). Collection of juveniles of Oreochromis niloticus was done from Lake Ziway from 2:30pm to 04:00 pm in June 21, 2008, from Lake Koka from 10:00am to 12:00am in June 22, 2008, from Lake Hora from 10:30am to 11:30am in June 23, 2008 and from Lake Hawassa from 1:00pm to 3:00pm in June 25, 2008. During fish sample collection, some water quality parameters were measured (Table 1).
Table 1 : Some water quality parameter of the lakes measured during sample collection Temp. Cond. TDS Salinity Mortality at Lakes pH DO (%) (0C) (uS/cm) (PPT) (PPT) transportation Hawassa 24.3 8.7 87 795 437 0.12 6% Ziway 26 7.8 94 851 534 0.1 24% Koka 27.9 8.35 81.6 1084 757 0.1 15% Hora-A. 25.5 9.45 79.3 780 403 0.4 11%
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Fig. 5 : Collection of Oreochromis niloticus from different Ethiopian lakes
Immediately after capture, appropriate size of juveniles of O. niloticus was screened for other species as well, for large and small size of the same species, by hand picking. Polyethylene bags containing approximately 25 to 30 litres of water and oxygen cylinder containing 24 litters of pure oxygen were used to transport about 200 individual juveniles O. niloticus (Fig..5). Depending on the distance between the lake and the research centre, the fish were provided oxygen more than once.
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Fig. 6 : Preparation of fish collected from Lake Hora for transportation to NFARRC (the arrow indicates the portable oxygen cylinder containing pure oxygen)
At the study site, the polyethylene bag containing the fish was immersed into the pond about for 20 minutes to acclimatize the fish to the new water condition such as temperature and pH. Moreover, the polyethylene bag was tied off and flow of water into the bag allowed to make an equilibrium condition so that the fish could swim and move to the pond. Then, the juveniles of O. niloticus were stocked into acclimatization ponds from time of collection (June 21-25, 2009) to July 16, 2008. After acclimatization, fifty juveniles of O. niloticus (10-15g weight and 8-10cm length) were randomly selected from all strains and stocked into separated experimental ponds. The stocking density of the fish was 2 fish m -2 (Eknath et al ., 1993; Nandlal and Pickering, 2004). The experiment was done in triplicate. The total number of fish at the start of the experiment was 600 fish (50 fish * 12 = 600 fish). Thus, the total biomass at the start of the experiment was 7488g (600fish*12.48g mean weight of the whole fish). To maintain the water quality of the ponds, there was a continuous water supply throughout the experiment. In addition, all the ponds were covered with nets to protect the fish from fish-eating birds (Fig.6).
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Experimental Design : Three similar-sized (10m x 10m x 1.5m) of ponds were selected randomly (Fig. 7). Pond preparation was done on June 13 to 19, 2008. All the three ponds were cleaned on June 13 and 14, 2008 and left for one week for drying. Then, each pond was partitioned into four parts using nets on June 18 and 19, 2008 as indicated in Fig. 2.6. All the ponds were filled with water at 100cm water level on June 20, 2008. The experimental fish were collected from four lakes described above from June 21- 25, 2008. All the juvenile of O. niloticus strains were stocked in acclimatization pond for three weeks. Then the appropriate weight and length of the experimental fish were transferred to the experimental ponds (Fig. 7).
Fig. 7 : Three experimental ponds indicating the partitions used for stocking the different Nile tilapia strains
Feeding and Feed Supplements : The experimental fish were fed two times a day at 10:00 and 17:00 hours with the feed produced by Akaki feed factory. The fish were fed when the daily surface water temperature was warmer (Tran-Duy et al ., 2008). At warmer temperature the feed intake of the fish is higher than at cold water temperature. According to Abdel-Tawwab, (2004) the feeding rate (feeding ration) was 3% of the body weight of the fish per day throughout the experiment. The nutritional composition of the diet used for the experiment was 89.69% dry matter which contains 92.18% organic matters and 7.82% ashes. About 23 % of the organic matter is crude proteins. The ash also contains Phosphorus (0.08%), Nitrogen (2.2%), Calcium (0.19%), Magnesium (0.32%), Iron (0.355%).Potassium (1.09%), and sodium (79.9%). The amount of the feed was adjusted once in two weeks based on the body weight of the fish. Thus, the amount of daily supplementary feed or daily feed ration (DFR) was calculated using the average body weight (ABW), the total number of the fish (N) and the feeding rate per day (FR d -1) using the following formula: DFR = ABW x N x FR d -1 (Nandlal and Pickering, 2004). Water quality parameters : During the experiment, the water quality parameters such as temperature, dissolved oxygen concentration, pH, were measured daily. Total dissolved solid particles (TDS), conductivity and salinity were measured once in two weeks. Some water quality indicator macroinvertebrates were also collected. Sampling of fish and measuring of growth parameters: 20 to 25 fish were sampled for body weight and body length measurement every two weeks to determine how much the fish have been grown. Length and weight of the fish were measured using ruler and digital weight balance (Ohaus portable balance) (Fig.10). Mortality of the fish was also registered throughout the experiment. Sexual maturity and other effects were also registered for all strains (Fig. 11).
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Fig. 8 : Feeding, removing of dead fish and cleaning of the ponds during the experiments.
Fig. 9 : Measurement of some water quality parameters (such as temperature, pH, Conductivity salinity and observation of some indicators macroinvertebrates
Fig.10 : Measuring of fish body length and fish body weight using ruler and Ohaus portable balance respectively
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Fig. 11 : Testing of sexual maturity and abnormality of fish
Growth parameter measurement: The use of growth model is essential to describe the growth performance and growth pattern of the fish in a given environmental conditions (Bureau et al ., 2000). It is also very important to produce production and environmental management plan (Iwama and Tautz, 1981). Using growth model, growth rate of fish at different sampling times, feed conversion ratio of the farmed fish, and amount of feed to be given for them can be estimated. The most popular growth model is specific growth rate. It is very important model to determine the growth rate of the fish on the bases of natural logarithm corresponding to body weight of the fish (Halver and Hardy, 2002). At a constant water temperature cubic root of the live body weight of the fish (e.g. Salmonids) increases linearly with time (Iwama and Tautz, 1981). Specific growth rate and survival rate : Mortality of the fish was counted from the time of transportation to the end of the experiment. Based on the data collected during the experiment, rate of survival and growth performance were computed (Hardy, 2002; Ridha, 2006). The most widely used growth performance parameters (namely: specific growth rate (SGR) and rate of survival) were calculated using the following formulae:
-1 SGR (% day ) = ( (lnW f – lnW i )/ dt )X 100
Survival rate (%) = (NSF – NDF/NSF) x 100
Where: Wf and W i are the final and initial body weight of the fish, respectively; dt is the time interval in days during the study period, NSF and NDF are the number of stocked and dead fish during the study period, respectively
The growth performance parameters were calculated at different sampling period to compute the growth performance and growth pattern of each strain throughout the experiment.
Feed conversion ratio and feed efficiency ratio : Feed conversion ratio (FCR) was calculated using the amount of feed intake of the fish in gram (g) and body weight gained in gram (g) during the experiment. Gross fish yield (GY) was also calculated from the total body weight of the cultured fish and volume of water used for rearing the fish. Feed conversion ratio and gross fish yield were calculated using the following formulae (Ridha, 2006):
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FCR = F I (g)/ W g (g) GY = W f/W v Where: FI is amount of feed intake (g) in dry weight basis, Wg is Weight gain in gram (g), Wf is final total fish weight, Wv is the total water volume used for culturing fish in metre cube (m 3)
Length-weight relationship and Fulton’s condition factors : Length-weight relationship is important growth parameter to predict the growth rate and growth pattern of the fish. Fulton’s condition factor is also an important growth parameter which indicates well being of the fish (Bagenal and Tesch, 1978). It was calculated for each of the strain at different sampling periods using the following formula.
3 FCF = W T / L T X 100 3 Where: WT is the total weight of the fish (g) and L T is the total length fish (cm)
Statistical Analysis: Mean growth performance parameters, survival and feed utilization were analysed for all strains at different sampling periods using analysis of variance (General Linear Model). T-test and Turky test were used to identify the mean value that causes a significant difference for the analysis of variance. Statistical significance was determined at p<0.05. All calculation was performed using Minitab 15 and SAS 9.1 version statistical softwares.
Results Water quality : The mean value of some water quality parameters were calculated and are summarized in Table 3.1. All the ponds have similar water quality values whichwere not significantly (p > 0.05) different among triplicates of the ponds. Table 1 . The mean value of some water quality parameters measured during the experiment Temperature DO Conductivity TDS Salinity Lakes pH (0C) (%) (uS/cm) (PPT) (PPT) Pond 1 20.38a 8.36b 86.40c 173.02d 99.25e 0.1 Pond 2 20.42a 8.29b 88.10c 188.66d 97.9e 0.1 Pond 3 20.38a 8.27b 87.22c 176.46d 92.62e 0.1
Growth in weight and length : The growth performance for triplicates of all the O. niloticus strains was computed. In all parameters there was no significant (p>0.05) variation among triplicates of same strains (Appendix III).The initial mean body length and initial mean body weight of all the strains were computed and are presented in Table 3.2. There was no significant (p>0.05) difference among the strains in their initial mean body length and initial mean body weight. This indicates the initial body size of all the strains were homogenous.
Table.2 . Growth parameters of four O. niloticus stains in pond culture Initial mean Initial mean Final mean Final mean Mean weight Survival Sex. length weight length weight gain rate. Mat. (cm/fish) (g/fish) (cm/fish) (g/fish) (g/fish) (%) Strains AS 9,14+0,06a 12,60+0,22a 15,10+0,08a 59,63+2,07ab 47,03+2,02ac 100 0 ZS 9,15+0,08a 12,49+0,11a 14,30+0,16b 53,13+1,22a 40,63+1,11b 96 0 HS 9,18+0,11a 12,44+0,34a 14,58+0,20b 55,83+2,29a 43,40+2,01bc 100 0 KS 9,25+0,07a 12,40+0,32a 15,30+0,23a 64,04+3.97b 51,64+3,83a 100 2 fish **In each row, data with different letter are significantly different (p<0.05); AS, ZS, HS, KS are Hawassa, Ziway, Hora-Arsedi and Koka strains, respectively.
The final mean body length, final mean body weight, weight gain and rate of survival of all the strains were calculated after 60 days of the experiment and were summarized in Table 3.2. The highest and the lowest final mean body weight were observed in Koka strain (64.04+3.97g) and Ziway strain (53.13+1.22g), respectively. The Koka strain had significantly (p<0.05) higher final mean body weight 90 Ma nagement of shallow water bodies ..., EFASA 2010 than the Ziway and the Hora strains, but there was no significant (p>0.05) difference between final mean body weight of the Koka and the Hawassa strains. The final mean body weight of the Hawassa strain was slightly higher than the final mean body weight of the Hora and the Ziway strains, but there was no significant difference among the three strains. The final mean body length of all the strains revealed significant (p<0.05) difference among the strains. The Koka and the Hawassa strains had significantly higher final mean body length than the Ziway and the Hora strains, but there was no significant (p>0.05) difference between the final mean body length of the Koka and the Hawassa strains. Likewise, there was no significant difference between the Ziway and the Hora strains. The growth pattern of the four Nile tilapia strains showed similar trend (Fig. 12 and 13). For the first two weeks’ culturing periods, change in length was greater than change in weight for all strains. Later, change in weight was higher than change in length. This indicates that at later stage of growth, fish grow more in weight than in length. Survival rate of all the strains was very high ranging from 96% to 100%. Moreover, sexual maturation was detected in the Koka strain at 19cm and 20.2cm length of fish with body weight of 101g and 132g, respectively.
70
Variable 60 MBW (g) of AS MBW (g) of ZS MBW (g) of HS MBW (g) of KS 50
40
Weight (g) Weight 30
20
10 0 1 2 3 4 5 6 7 8 9 Rearing period in weeks
Fig. 12 : Variation in body weight of four Nile tilapia strains throughout the experiment
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16
15 Variable MBL(cm) of AS 14 MBL(cm) of ZS MBL(cm) of HS MBL(cm) of KS
13
12 Weight (g)
11
10
9 0 1 2 3 4 5 6 7 8 9 Rearing period in weeks Fig.13 : Variation in body length of four Nile tilapia strains throughout the experiment
Specific growth rate (SGR): At the end of the experiment, the highest and the lowest specific growth rate was achieved in Koka and Ziway strains, respectively. The Koka strain had significantly (p<0.05) higher specific growth rate than the Ziway and the Hora strains, but there was no significant (p>0.05) difference between the Koka and the Hawassa strains. The Hawassa strain had also significantly higher specific growth rate than the Ziway strain, but there was no significant difference from the Hora strain. Similarly, there was also no significant difference between the Ziway and the Hora strains. Difference in specific growth rate due to strains and sampling period are clearly indicated in Fig. 14 and Fig. 15, respectively.
Table 3 : Growth parameters (Specific Growth Rate (SGR), Daily Growth Rate (DGR), Feed Conversion Ratio (FCR), Fulton’s Condition Factor (FCF) and Gross Fish Field (GY)) of four O. niloticus strains in pond culture Strains SGR (% day -1) DGR (g fish -1 day -1) FCF FCR GY (g m -3) AS 2.59+0.07ac 0.78+0.04a 1.73+0.06a 1.76+0.03a 149.08+1.78 ab ZS 2.41+0.14b 0.68+0.09b 1.82+0.03a 1.73+0.05a 131.04+4.16a HS 2.50+0.10bc 0.72+0.08ab 1.80+0.05a 1.73+0.05a 139.58+4+12a KS 2.73+0.22a 0.86+0.13a 1.79+0.03a 1.72+0.05a 160.09+6.17b **In each row, data with different letter are significantly different; As, ZS, HS; KS are Hawassa, Ziway, Hora and Koka strains, respectively
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Fig.14 : Specific growth rate of four O. niloticus strains after 60 days of culturing period
Fig. 15 : Variation in specific growth rate between sampling periods for each tilapia strain
Feed conversion ratio and gross yield : After 30 days culturing period, feed conversion ratio was computed. The highest feed conversion ratio value was observed in the Ziway strain followed by the Hawassa strain. The best (lowest) feed conversion ratio was observed in the Koka strain. The result indicated that there was significant difference between the Koka and the Ziway strains in their feed conversion ratio. But both strains were not significantly different from the Hawassa and the Hora strains (Fig.3.5). However, at the end of the experiment, statistical analysis revealed that feed conversion ratio was not significantly different among all the strains (Table 3 and Fig.16). For all the strains, the value of feed conversion ratio increases with time implies decreasing in feed efficiency (Fig 17). At the end of the experiment, gross fish yield for all strains was computed. The highest gross fish yield was achieved in Koka strain followed by Hawassa and Hora strains, respectively. The Ziway strain had the lowest gross fish yield. Statistical analysis revealed that the Koka strain had significantly higher gross fish yield than the Ziway and the Hora strains, but there was no significant difference between the gross fish yield of Koka and Hawassa strains (Table 3 and Fig. 18).
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Fig. 16 : Feed conversion ratio of four Nile tilapia strains after 30 and 60 days sampling periods (bars having different letters are significantly different at P<0.05)
Fig. 17 : Variation in feed conversion ratio between each sampling period for each strain
Fig.18 : Gross fish yield of four nile tilapia strains calculated at the end of the experment (after 60 days); (bars having different letters are significantly different at P<0.05).
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Length-weight relationships and Fulton’s condition factor : The length-weight relationship of all the O. niloticus strains is presented in Fig. 3.8. The length-weight relationship for each of the strains was expressed by the following linear logarithmic equations:
Log W = -1.83 +3.04log L for L. Hawassa strain, Log W = -2.66 +3.78log L for L. Ziway strain, Log W = -2.49 +3.63log L for L. Hora-Arsedi strain, and Log W = -1.75 +2.99log L. for L. Koka strain.
As indicated in Fig. 3.8, there was a strong relationship between length and weight for all strains. The Koka strain had slightly higher ‘R 2’ value (93.5%) than the Hawassa strain (88.0%), the Ziway (87.7%) and the Hora strains (89.12%).
Table 4 : Estimated parameter of length-weight relationship for four O. niloticus strains
Strains ‘a’ ‘b’ ‘R 2’ Remark AS -1.83 3.04 88 3 is growth exponent (b) ZS -2.66 3.78** 89.5 value that shows isometric HS -2.49 3.63 90.5 growth KS -1.75 2.99 93.5 ** Indicate that b for ZA revealed significantly (p<0.05) different from 3.
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A B
140 S 0.0505744 110 S 0.0485718 R-Sq 88.0% R-Sq 89.5% R-Sq(adj) 87.8% 100 R-Sq(adj) 89.4% 120 logW = - 1.83 + 3.04 logL logW = - 2.66 + 3.78 logL 90
100 80
70 80 60
60 50 W eight of the fish (g) W eight of the fish (g) 40 40 30
20 20 12 13 14 15 16 17 18 19 12 13 14 15 16 17 18 Length of the fish (cm) Length of the fish (cm)
C D
120 S 0.0343783 S 0.0388743 140 R-Sq 90.5% R-Sq 93.5% 110 R-Sq(adj) 90.3% R-Sq(adj) 93.4% 100 logW = - 2.49 + 3.63 logL 120 logW= - 1.75 + 2.99 logL
90 100 80
70 80
60 60 W eight of the fish (g)
W eight of50 the fish (g)
40 40
30 20 12 13 14 15 16 17 18 12 13 14 15 16 17 18 19 20 21 Length of the fish (cm) Length of the fish (cm)
Fig.19 . Length-weight relationship showing a logarithmic equation for each of the four Nile tilapia ( O. niloticus) strains: A, B, C and D represent for Hawassa, Ziway, Hora and Koka strains, respectively
The growth exponent (b) in the growth equation is also presented in Table 3.4. The growth exponent of the Ziway strain (3.37) had significantly higher value than 3, but all the other strains were not significantly different from 3. The fitted curve for Koka and Hawassa strains was slightly different from the growth pattern of Ziway and Hora (Fig. 19).
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140 Variable AS -W * AS -L 120 ZS-W *ZS-L HS -W *HS -L KS -W * KS -L 100
80
Weight (g) 60
40
20 12 13 14 15 16 17 18 19 20 21 Length (cm)
Fig. 20 : Comparison of the fitted plot curve for length-weight relationship of four Nile tilapia strains (AS- Hawassa strain, ZS-Ziway strain, HS- Hora strain and KS-Koka strain)
At the beginning of the experiment, Fulton’s condition factor was calculated for each of the strain. There was significant (p<0.05) difference among the strains. The Hawassa strain had significantly higher Fulton’s condition factor than the Koka strain, but there was no significant difference from the Ziway and the Hora strain (p>0.05). Similarly, there was no significant difference among the three strains (Koka, Ziway and Hora strains) in their Fulton’s condition factor value. However, at the end of the experiment, there was no significant difference among all the strains (Fig. 20). As indicated in Fig. 21, there was a direct relationship between Fulton’s condition factor and culturing period thoughout the experiment.
Fig.21 : The pattern of Fulton’s conditional factor for four O. niloticus strains at different sampling intervals [bars having different letters are significantly different (p<0.05)]
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Discussion Water quality parameters : Some water quality parameters measured during the study period remained in agreement with the favourable range set for O. niloticus (Trewaves, 1983). The average surface water temperature was 20.9 0C with slightly basic pH condition (8.37). However, this temperature was much less than that of the temperature ranges (28 0C to 30 0C) for maximum growth set for Oreochromis niloticus (Beamish, 1970). In this study, triplicates of all the strains were not significantly different in their growth performance and feed conversion ratio. This means that the effect of environmental factors on the growth performance of all the strains were similar for all experimental ponds. In addition, the initial mean body weight and initial mean body length of all the strains were not significantly different indicating homogenous initial fish size. Growth performance : In the present study, growth performance was significantly different among the strains. The Koka strain had the highest growth performance while the Ziway strain had the lowest growth performance. The body weight of the Koka strain was nearly 20.53%, 14.71% and 7.4% higher than that of the Ziway, the Hora and the Hawassa strains, respectively. The specific growth rate of the Koka strain was also nearly 13.28%, 9.2% and 5.41% higher than that of the Ziway, the Hora and the Hawassa strains, respectively. The results obtained in this study were in line with the work of Abdel-Tawwab (2004), who worked on the growth performance of four different Nile tilapia strains collected from four Egyptian lakes (Abbassan, Asswan, Manzalah and Maryut lakes). The author reported that the Asswan strain had higher growth performance than the other strains tested. The Asswan strain had the highest final body weight. The Manzalah strain had the lowest final body weight. The final body weight of the Asswan strain was nearly 29.97% higher than that of the Manzalah strain. Ridha (2006) made a similar observation and reported that different stains had different growth performance and feed conversion ratio. The study indicated that the selected line (SL) and the GIFT strain had higher mean body weight, daily and specific growth rates than the non selected (NS) strain. In this study, the selected line showed the highest value of daily growth rate followed by the GIFT strain. Similarly, the highest specific growth rate was obtained in the Selected Line followed by the GIFT strain. The lowest daily growth rate and specific growth rate were obtained in Non Selected strain at 125 fish m -3 stocking density of Juvenile of Nile tilapia. The specific growth rate that ranged from 2.59+0.07 to 2.73+0.22% day -1 obtained in this study was comparable with the range of 2.2 to 3.1% day -1 reported by Middendorp (1995) for juvenile of Nile tilapia in pond culture. Moreover, the specific growth rate observed in this study was much higher than the specific growth rate that ranged from 0.49 to 0.75% day -1, 0.787 to 1.035 % day -1 and 0.967+0.03 to 1.277+0.03% day -1 reported by Al Hafedh (1999), Ashagrie, et al. (2008) and Abdel-Tawwab (2004), respectively obtained for juveniles of Nile tilapia. The daily growth rate ranged from 0.68 to 0.86g fish -1 day -1 in this study and was in line with the range of 0.5 to 1.186g fish -1 day -1 reported by Middendorp (1995) for juveniles of Nile tilapia in pond culture. The daily growth rate was also comparable with the range of 0.45 to 0.66 86g fish -1 day -1 reported by Cruz and Ridha (2001) for fingerlings of Nile tilapia in tank culture. The result of this study clearly indicated that the Ziway strain had the poorest growth performance among the other strains tested. This result is in line with the work of Admassu and Ahlgren (2000) on the growth performance of three juvenile of Nile tilapia strains in three Ethiopian Rift Valley Lakes. They reported that the growth performance of juveniles of Nile tilapia strain in Lake Ziway showed the lowest growth performance than found in Lake Chamo and Lake Langano. Thus, the present study together with the study of Admassu and Ahlgren (2000) confirmed that the growth performance of the Ziway strain is relatively low. Eknath et al . (1993) and Palada-de Vera and Eknath (1993) had comparative studies on the growth performance of eight different Nile tilapia strains collected from Egypt, Kenya, Senegal, Ghana, Israel, Taiwan, Singapore and Thailand. The authors found that African strains had higher growth performance than Asian strains with the exception of Ghanaian strain. The fastest growth rate was observed in Egyptian strain while the poorest growth rate was obtained in Ghanaian strain indicating that different Nile tilapia strains had different growth performance. In line with this study, the present result showed that variation in growth performance occurred among the four 98 Ma nagement of shallow water bodies ..., EFASA 2010 strains tested, i.e. the Koka strain had the fastest growth rate while the Ziway strain had the poorest growth rate. Similarly, the body weight of the Hawassa strain was significantly higher than that of the Ziway strain. The daily and specific growth rates of the Hawassa strain were nearly 14.71%, and 7.47% higher than that of the Ziway and the Hora strains, respectively. Thus, the growth performance of the Koka strain was ranked first followed by the Hawassa and the Hora strains, respectively. The Ziway strain had the lowest growth performance. Therefore, ranking of growth performance of different strains is possible. However, ranking of growth performance for different Nile tilapia strains may be affected by environmental factors as well as environment-genotype interaction (Abdel-Tawwab, 2004). Thus, it is crucial to consider different factors when candidates of the strain are selected for aquaculture purpose. The result of the present study also showed that fish survival was reasonably good in all strains (96% to 100%) and was not influenced by strain differences. This result is in line with the work of Ridha (2006) who observed that the survival rate of juveniles of Nile tilapia was relatively high for all strains (97.4 to 100%) in tank culture. Similar result was reported by Ashagrie et al ., (2008) who found that survival of juvenile of Nile tilapia was between 94% and 97% at different stocking density in cage culture. El- Sayed (2002) also observed that the survival rate of Nile tilapia fry was between 90% and 100%. In this study, sexual maturation was also observed in Koka strain at 101g and 132g body weight. This result was much higher than Suresh (2003) who reported that sexual maturation was observed at 30g to 50g body weight of Nile tilapia. Feed conversion ratio : The lowest feed conversion ratio implies the most efficient nutrient utilization and conversion into flesh. In the present study, the Koka strain had the highest growth performance with slightly better feed conversion ratio than the other strains. Similarly, Abdel-Tawwab (2004) reported that the lowest feed conversion ratio was obtained in Aswan strain that had the highest growth performance. In the same study the highest feed conversion ratio was obtained in Abbassan and Manzalah strains that had the lowest growth performance in the groups. The feed conversion ratio that ranged from 1.72 to 1.76 obtained in this study was in line with the range of 1.45 to 2.40 for juvenile of Nile tilapia, reported by Yi et al. (1996) in cage culture. Moreover, feed conversion ratio observed in this study was much less than the feed conversion ratio (3.15 to 4.86) for juveniles of Nile tilapia reported by Al Hafedh (1999). However, it was slightly higher than the feed conversion ratio that ranged from 1.01 to 1.6 for juveniles of Nile tilapia reported by Diana et al . (2004) in pond culture. The study also showed that gross fish yield was also affected by strain differences. The maximum gross fish yield was obtained in the Koka strain (160.09g m -3) followed by the Hawassa strain (149.08g m -3). The lowest gross fish yield was obtained in the Ziway strain (131.04g m -3). The Koka strain had 22.17% higher gross fish yield than that of the Ziway strain. This result is in agreement with the work of Ridha (2006) who found that the strain with the highest growth performance (Selected line) had the highest gross fish yield (45.4+1.2kg m -3) and the lowest feed conversion ratio (1.27+0.01). The poorest growth performance (None selected line) had the lowest gross fish yield (30.4+0.08 m -3) and the highest feed conversion ratio (1.55+0.12). Length-weight relationship and Fulton’s condition factors (FCF) : In the present study, length-weight relationship of all the Nile tilapia strains showed a strong relationship (R 2 > 88% for all strains). The fitted plot curve for the Ziway and the Hora strains overlapped. This indicates that both of the strains have similar trend in their growth pattern than others. The fitted curve for the Koka and the Hawassa strains were relatively different. The difference progressively increased as the weight and length of the fish increased. Thus, the growth pattern of the Koka and the Hawassa strains was slightly different from that of the Ziway and the Hora strains. This result is in agreement with the work of Admassu and Ahlgren (2000) who reported that the growth pattern of the same species in Lakes Chamo, Langano and Ziway. The strains from Langano and Ziway lakes had similar growth pattern. The fitted plot curve for Chamo strain was slightly different from the other two strains. Thus, the growth pattern of slow and fast growing strains is different. The range of Fulton’s conditional factor (1.58 to 1.82) obtained in this study was also comparable with the average value of 1.46 in Lake Ziway and 1.86 in Lake Chamo reported by Admassu and Ahlgren (2000).
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With the exception of Ziway strain, the growth exponent ‘b’ of length-weight relationship obtained in this study was nearly 3 (a growth exponent ‘b’) that indicates an isomeric growth pattern. This means that the fish shape is consistent (Ariyaratne, 2004). The Ziway strain, however, had a growth exponent of 3.78. Thus, the Ziway strain had allotropic growth pattern and was heavier because of the weight increase (Halver and Hardy, 2002).
Conclusions and recommendations The main focus of this study was to compare the growth performance of different Oreochromis niloticus strains collected from different Ethiopian lakes. Comparison was made based on different growth performance parameters. These include specific and daily growth rates as indicator of growth, feed conversion ratio as indicator of feed utilisation efficiency, gross fish yield as indicator of production potential, and length-weight relationship as indicator of growth condition and growth pattern of the fish. The result of this study clearly demonstrated that the growth performance of different Nile tilapia strains was significantly different. The Koka strain had the highest growth performance and feed utilization efficiency than the other strains tested. The poorest growth performance was observed in the Ziway strain. It is worth to say that the best growth performed strain (Koka strain) had best feed utilization efficiency and had the highest gross fish yield at harvest. Thus, it is very important to select the correct strain for the enhancement Nile tilapia aquaculture production. Therefore, it is recommended that Nile tilapia hatcheries in Ethiopia should use Koka strain than other strains tested for fry propagation. However, further research is still needed to compare more strains at different life stages as well as at different environmental conditions to evaluate the robustness and the genetic potential of the strains to utilize as base population. Thus, the expected genetic differences between groups of fish (strains) can be used for efficient selection of the strains that could be utilized for the development of fish culture and breeding program in the country.
Acknowledgments We would like to thank Professor Hans Magnus for his advice and the National Fishery and Other Aquatic Resources Research Centre (NFARRC) for the opportunity to do this experiment in the research centre and providing all the facilities needed for the experiments. The manager of NFARRC Mr. Kassahun Assaminew and the Administrator Mr. Aschalew Lakew and all staff members are thanked for their full support. Dr. Getnet G/Tsadik, Dr. Zenebe Tadesse, and W/r Abeba W/Gebreal provided advice and valuable comments during the experiments. The Ziway Fisheries Research Centre provided materials during sample collection and financial support was provided by the Norwegian Government State Educational Loan.
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Technical and socio-economic characteristics of fishing activities, fish handling and processing in Ethiopia
Abera Degebassa, Zeway Fishery Resource Research Center (OARI)
ABSTRACT : Fish is an important source of food and income to many people in the developed world. In Africa, some 5 percent of the population, about 35 million people, e depend wholly or partly on the fisheries sector for their livelihood. Various traditional methods are employed to preserve and process fish for consumption and storage. These include smoking, salting, boiling, drying, canning, marinating and different combination of these. In Ethiopia, since early days fish had been consumed fresh and it is still the wish of many people to eat fish fresh as soon as possible after catching. This has been one of the limitations of fish consumption in many countries, especially in warm climates like Ethiopia. Fish are one of the most perishable foods known. It needs careful handling and processing. Careless procedures will accelerate spoilage and increase losses. But careful methods will retard spoilage, reduce losses and improve the quality of the marketed product. The process of handling and distribution of fish in Ethiopia is handled by fishermen, licensed traders, informal sectors and Fish Production and Marketing Enterprise (FPME).However, the bulk of fish marketing channels in Ethiopia is handled by FPME and is in fact the major supplier of fresh and processed fish for Addis Ababa market all year round. Facilities such as jetties which are important for fish handling are almost non existent, with the exception of some lakes at particular sites. There is also shortage of ice and other necessary materials which are crucial during boarding and landing. FPME with its facilities such as cold storage, ice making machine and insulated trucks with the necessary cold chain is in proper hygienic standard of fish until it reaches the consumers. However, informal sectors particularly the traders who mostly operate during the peak season transport whole fresh fish without ice in rented open trucks. Small traders regularly use pack animals to reach less accessible destinations while informal fishermen walk long distances by carrying fish in sacks on their heads in order to get their catch to traditional markets. Such kind of inadequate and unhygienic distribution systems pose public health concern and fast deterioration of fish which indirectly affects income of fishermen. In recent years, there is an increasing consumer preference for fresh and processed fish, particularly in urban areas and this offers considerable scope for further expansion. Hence, the reduction of post-harvest losses through improved handling and processing, transport and distribution systems should make an important contribution to the betterment of fishery sectors.
Key words : Fishing activities, fish processing, fish preservation, Ethiopia
Introduction Fish is an important source of food and income to many people in the developed world. In Africa, some 5 percent of the population, about 35 million people, depend wholly or partly on the fisheries sector for their livelihood (Somerset and Bowerman, 1996; FRDC, 2001).Various traditional methods are employed to preserve and process fish for consumption and storage. These include smoking, salting, drying, boiling, marinating and different combination of these. In Ethiopia, since early days fish has been consumed fresh, and it is still the wish of many people to eat fish fresh as soon as possible after catching. This has been one of the limitations of fish consumption in many countries, especially in warm climates like Ethiopia. Foods generally can be classified into stable, semi-perishable and perishable foods, depending upon the length of shelf-life they will keep. Unfortunately, fresh fish belong to the last group; in fact they are one of the most perishable foods known (Clucas and Satcliffe, 1981). Hence, before embarking on proper handling and processing, I would like to mention why fish is the most perishable food or what causes the spoilage or fresh fish after catch. Causes of fish perishability : It is known that fish spoilage (deterioration) may be caused by three agents. (i) Autolytic spoilage (deterioration): At the death of fish, food supply ceases and the energy resources soon become depleted. The energy continues to operate, but as energy is required to build the larger unit of the body, their function postmortem is the break down of compounds into smaller units. This break down of tissues affects the flavor lose, texture and sometimes, the appearance of the fish. The enzymes are present in the muscle of fish, viserca and digestive tract. They are also produced by
104 Ma nagement of shallow water bodies ..., EFASA 2010 bacteria. If viserca and gut bacteria are allowed to break down fish tissues, they will spread out of the gut, attack other areas of the fish, and cause belly burst which is a sign of advanced spoilage.Fish which have fed heavily before capture will have high enzyme concentration in the gut, and unless these are removed, the chance of belly burst will increase (Sikorski1990). (ii) Microbial deterioration : Although the newly caught fish is sterile, millions of bacterial and other microorganisms, many of them potential spoilers , are present in the surfaces slime , on the gills and in the intestine of living fish, but the do not harm because the natural resistance of healthy fish keeps then at bay. Soon after the fish dies, however, bacteria begin to invade the tissue, which provides an ideal medium for their growth and multiplication. The spoilage bacteria first utilize the similar components and in the process release various volatile off- odor components (FAO 1991b). The continued action of micro-organisms affects the appearance and physical properties of several components of the body. The slime on the skin and gills initially watery and clean becomes cloudy, clotted and discolored. The skin loses it bright indescent appearance. (iii) Lipid deterioration : Fish flesh consists of lipids which contains a high degree of polyunsaturated fatty acids chains. The most important causes of deterioration is oxidative rancidity.The polyunsaturated fatty acids which are subjected to attack by atmospheric oxygen, give rise to rancid flavor and subsequently to a series of other chemical reactions. Preservation and processing : There are two main ways by which spoilage can be slowed down or stopped: preservation and processing. Preservation methods keep the fish in the fresh state so that the changes in texture, taste and appearance, etc, are minimized. Processing methods usually change these properties so that the deterioration is slowed or halted, but the characteristics of the fish also alter according to the process used. Two different methods of preservation have been developed to reduce or inhibit enzyme and microbial spoilage of fish. Fish can be preserved broadly in two ways. (i) Temperature control : The bacterial flora of the fish and enzyme present in the tissues are adapted to the temperature at which the fish lives i.e. about 5-10 0C in cold water and 25-30 0c in the tropics. The bacterial and autolytic spoilage rates can therefore be reduced by lowering or raising the temperature. In broad terms, the lower temperature the slower the bacterial and enzyme activity will be and the longer the storage life. A fish can therefore be chilled or frozen to preserve it. The most important means of preservation of fresh fish in tropical and temperate climates is by chilling. The most common chilling media is wet ice. The other is freezing. The purpose of freezing fish is to lower the temperature and thus slow down the rate of spoilage by reducing the reaction of enzymes involved in autolysis as well as slowing the growth rate of bacteria. When the product is thawed after cold storage, it can be virtually indistinguishable from fresh fish depending on the time and temperature involved. (ii) Raising the temperature : During canning the fish are subjected to high temperature to kill bacteria and inactivate enzymes. The product must then be protected from further bacterial contamination by being hermetically sealed within the can. Canning also enables man to preserve the fish in un- edible conditions under a wide range of storage conditions for long periods. The other method is boiling fish in water is a method of short- term preservation used in many countries especially in south East Asia. The action of boiling fish in water denatures or cooks the protein and enzymes and kill many of the bacteria present on fish. The normal spoilage that occurs in a dead fish is thus stopped or drastically reduced. (iii) Marinating is a process by which fish are protected by placing the fish in a solution of usually acetic acid and salt in order to retard the action of bacteria and enzymes. Lowering of water activity: (i) Drying a preservation method of fish based on the principle that reduced moisture content and therefore, reduce water activity will inhibit microbial growth, enzymic and most chemical reactions and so retard deterioration. (ii) Smoking is a method of preservation affected by the deposition of naturally produced chemicals resulting from the pyrolysis of wood in combination with drying and after salting. The smoke produced from burning wood contains a large number of compounds, some of which kills bacteria. The smoke also generates heat which will dry and cook the fish flesh and thus destroy the enzyme activities and prevents spoilage. (iii) Salting alone, or in combination with drying/smoking is an ancient method of preserving fish still very much in use today. As salt is applied in to the flesh, water is removed from the fish flesh due to osmosis and the water activity is reduced to 0.75. Growth of most spoilage bacteria is inhibited at 0.75 water activity. As most
105 Ma nagement of shallow water bodies ..., EFASA 2010 bacteria cannot grow in salt concentration above 6%, salting will, therefore, reduce bacterial action (Johonson and Clucas, 1996) Fish handling and processing-some aspects of experiences in Ethiopia : Fish is one of the most perishable foods known. It needs careful handling and processing. Careless procedures will accelerate spoilage and increase losses. But careful methods will retard spoilage, reduce losses and improve the quality of the marketed product. The process of handling and distribution of fish in Ethiopia is handled by fishermen, licensed traders, informal sectors and Fish Production and Marketing Enterprises (FPME). However, the bulk of fish marketing that passes through marketing channels in Ethiopia is handled by FPME and it is in fact the major supplier of fresh and processed fish for Addis Ababa market all year round. The varied experience of handling fish in the different sites is discussed below. Handling of fish at boarding and landing sites : Facilities such as jetties which are important for fish landing are almost non-existent, with the exception of some lakes at particular sites. There is also shortage of ice and other necessary materials which are crucial during boarding and landing. In many lakes, gill net fish fishermen come to fishing grounds in the afternoon to set their nets and return the following morning to collect their catch. Fishermen that use beach seine and long lines normally fish early in the morning and return late morning to the landing sites. They store their catches in the boat until the collection boat or truck arrives, or fish are dumped on the sandy beaches with or without shade. The time lapse between capture and arrival at the receiving station is very long (an average of 5-7 hrs). No efficient cold chilling is used ( ice is seldom used except by FPME) andsuch practices induce heavy post-harvest losses and poor quality of fish . Handling fish during distribution : FPME with its facilities such as cold store ice machine insulated track and some 10-15 fish shops equipment with necessary cold chain is in afar better position in keeping proper hygienic standard of fish until it reaches the consumers. However the informal sector, particularly the traders who mostly operate during the peak season, transport whole fresh fish n rented open tuck .Small traders regularly use pack animals to reach less accessible destination while informal fishermen walk along distance by carrying fish in sacks on their heads in order to get their catch to traditional markets. Such kind of inadequate and unhygienic distribution system poses public health concern and fast deterioration of fish which indirectly affects the income of fishermen Fish Processing in Ethiopia : Fish processing in general is non- existent in Ethiopia. Fishermen around Lakes Zeway Chamo and Abay practice fish drying where they are unable to sell their catch in fresh form. Currying fish by salting is not popular in the inland fishing, mainly due to lack of knowledge on storage and salt, currying. Fish smoking is also not popular in the country. However, Zeway fishery research center has recently started smoking tilapia on experimental basis to diversify the fish markeket in the country. Canning of fish has recently been started by an Ethiopian meat concentration factory. Future improvement of fish handling and processing : Nowadays there is an increasing consumer preference for fish and processed frozen fish, particularly in urban areas. Therefore fish hasr considerable scope for farther expansion, however, adequate quantity of storage, landing facilities, processing and distribution centers are needed to cope up with the increasing demand for fish and supply quality fish to consumers. Therefore, the following recommendation should be given due consideration so as to promote fish consumption and improve livelihood and welfare of the fisherfolk community.
Recommendations The reduction of post-harvest loss through improved handling and processing transport and distribution system, should be given high priority, as it will make an important contribution to the betterment of the fishery sector. To do this and the following recommendation should be given consideration: • Distribution system should be geared to the form in which fish is to be sold. If it is to sell fresh fishermen in the first place must keep it in suitable condition which needs ice storage in their boats. Secondly, there must be adequate landing sites and storage facilities within the fishing sites. • If fresh and processed fish are to be transported to the market centers, the distribution be it is private or other organization, must collect and transport it in appropriate vehicles such as refrigerated or insulated trucks. 106 Ma nagement of shallow water bodies ..., EFASA 2010
• Methods of traditional or modern fish preservation such as drying, smoking or salting should be encouraged to improve the shelf life of fish, since fish serve as cheap source of protein, particularly to the poorest segment of the population in countries in Africa and south East Asia. • Where projects plan to improve processing or preservation techniques, special consideration must be given to the family relationship and tradition. If women are responsible for processing, it should be they who receive credits for new equipment. • Seasonality of fish catch and supply, which is the main characteristics of fishing activities in Ethiopia, could pose a problem for sustaining consumer interest and demand. Hence, an appropriate technology needs to be introduced for fish preservation over a prolonged period. • Considerable effort is required to create awareness among the population on the nutritional value of fish through appropriate channels like public media, schools, etc. Promotion and popularization of fish consumption should be strengthened. • There should be regulation with regard to quality control from the catch untill the selling site in order to protect the consumers from health hazards
Conclusion Fish being extremely perishable food stuff, it needs careful treatment in handling and processing, both from public health aspect and improvement of the welfare of fishing communities. The improvement of facilities from the point of production until it reaches the consumer is important. Therefore, adequate financial and institutional support is needed for construction of landing jetties, water supply, cold chains and appropriate transport facilities in addition to the promotion of traditional and improved preservation methods.
References Clucas, I.J. and Sutcliffe, P.J. (1980). An introduction to fish handling and processing. R eport of Tropical Products Institute, G143, 86pp FAO (1991b) Lake Victoria (Tanzania) Fisheries Development project. Roome. Food and Agriculture Organization of the United Nations. Johonson, S.E. and Clucas, I.J. (1996) Maintaining Fish Quality: an illustrated guide . Chatham, UK, Natural Resources Institute. Somorset, S. and M. Bowerman (1996). Enhanced usage of contemporary scientific finding on health benefits of sea food to promote fresh sea food consumption. Final report 1996/340, Fisheries Research and Development Corporation, Australia. 94p.
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Economic analysis of capture fisheries: The case of Lake Babogaya, Ethiopia
Lemma Abera Hirpo Negro Farm, P.O.Box 1335, E-mail: [email protected]
ABSTRACT: The study was conducted in Lake Babogaya, Debre Zeit town, situated some 45 km in the south east of Addis Ababa. The objective of the survey was to generate some baseline information for the economic analysis of capture fishery. Fishing of Oreochromis niloticus was conducted for the period of September 2005 to August 2006 using gillnets of 10 cm mesh sizes. The gear was set in the afternoon (05:00 pm) and lifted in the following morning (7.00 am). Then immediately after capture, some biological parameters of the fish as well as all inputs that are involved in the fishing activities were recorded. The fish were then processed and sold at local markets. The price of fish varied from 1-3 Birr/head depending on the demand of the product. The result indicated that the total income of fish varied between months and. the demand was high between March - April and August 2006. Hence, the study concludesd that the profitability of capture fishery of the lake was related with demand of the product in the area.
Key words/Phrases: Capture fishery, economics, Lake Babogaya, Oreochromis niloticus.
Introduction Agriculture being the main backbone of Ethiopia’s economy, fishery has also the potential to contribute to the economy of the country and is becoming a valuable asset in the economy. Even though Ethiopia is a land- locked country, it is endowed with a number of lakes and rivers, which are believed to be promising potentials of different fish stocks. Despite the high potential of fish resource to contribute to the economy, it is far lagging behind due to poorly developed infracstructure, human personnel and administrative structure in the fishery sector. This has contributed to underexploitation of the resource in certain areas and management problems of the sector. For instance, resources in all the rivers are not utilised by resource users but some are used mainly for fishing (Wudneh, 1998). Most Rift valley lakes harbour African catfish ( Clarias gariepinus ), Tilapia nilotica ( Oreochromis niloticus ) and a few cyprinids, mostly Barbus species (LFDP, 1998). Annual fisheries potential of the major lakes, reservoirs, small water bodies and major rivers in Ethiopia is estimated to be 51 thousand tones since 1993, and the catch in the year 1993 was estimated at 8 thousand tones (16% of the potential). In the year 1999 the total catch was estimated at 17,000t from the estimated potential of more than 75,000t/yr. Nile Tilapia ( Oreochromis niloticus ) is the dominant fish species in the landings (FAO, 1995, LFDP, 1998, EARO 2002). Catches are still falling far below the estimated potential yields, although some lakes are heavily exploited (for example, Lakes Ziway and Hawassa) (LFDP, 1998). Hence the contribution of fisheries to the GDP is very low. Concerning the gears, gillnets are the most commonly used fishing gears and long lines and beach seines are used depending on the fish species and the shorelines of the lakes. From 1993 to 1999, the trend of Ethiopian fishery showed an increasing trend in production. Despite the increase in production, Ethiopians prefer meat to fish, which is mainly attributed to the high population of cattle. Inhabitants near lake shore areas consume more fish, especially Tilapia which is the dominant species in the landings, (per head per year) than those living far from the resource area (LFDP, 1998). In some part of the country, the fishery industry has been of critical importance to the local economy and to the social well-being of communities and provides a vital source of food, employment, recreation, trade and economic well being for the people. In Lake Babogaya, prior to the beginning of the present study, there was limited fishing activity. The lake was mainly used for recreation and domestic water-use purposes. The reason for limited fishing activity in the lake could be due to lack of fishing gears and lack of knowledge on the fishery resource utilization. Therefore, this study aimed to generate baseline information on the profitability of capture fishery of the lake for the appropriate utilization of the fish resources by the local communities.
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Materials and methods Description of the study area : Lake Babogaya is one of the volcanic crater lakes found in the vicinity of Bishoftu town at about 45 Km East of Addis Ababa (Fig.1). The lake is small, roughly circular and fairly deep, and is found at an altitude of 1870 m and at about 9 0N latitude and 39 0E longitude (Prosser et al., 1968; Wood, et al ., 1984). Like the other volcanic crater lakes of the area, it is a closed system surrounded by very steep and rocky hills. The vertical distance from the lake's surface to the crater rim is 20 m, and this affords moderate protection from wind (Baxter, 2002). The lake is fed primarily by precipitation falling directly on its surface and run-off from its small catchment area (Prosser et al ., 1968), which was formed from volcanic rocks of basalt, rhyolite and tuff (Mohr, 1961). Limnological studies made on Lake Babogaya described its bathymetry (Prosser et al ., 1968) (Table 1), water chemistry (Prosser et al ., 1968; Wood et al., 1984; Rippey and Wood, 1985; Zinabu Gebre-Mariam, 1994; Baxter, 2002; Zinabu Gebre-Mariam, 2002), thermal stratification and mixing (Baxter and Wood, 1965; Wood et al ., 1976; 1984), chlorophyll a and phytoplankton (Wood and Talling, 1988; Zinabu Gebre-Mariam, 1994; Zinabu Gebre-Mariam and Taylor, 1997), bacterial abundance (Zinabu Gebre- Mariam and Taylor, 1997) and zooplankton associations (Green, 1986).
Fig. 1. Location of Lake Babogaya in relation to the other Bishoftu Crater Lakes (After Lamb, 2001)
Lake Babogaya is a dilute lake with Na + as the dominant cation and carbonate-bicarbonate as the dominant anion (Table 1). The lake water is alkaline, with the erosion of basaltic and hyper-alkaline rocks surrounding the lake playing an important role in increasing the alkalinity of the water (Wood and Talling, 1988). The phytoplankton community is dominated by blue-green algae, particularly Microcystis aeruginosa (Kutz.) (Wood and Talling, 1988), while the zooplankton is composed of copepods ( Afrocyclops gibsoni , Lovenula africana ), rotifers (Asplancha sieboldi , Brachionus calyciflorus and Hexarthra jenkinae) (Green, 1986), and Cladocera (Yeshimebet Major, 2006). The fish community in Lake Babogaya is composed of O.niloticus, C.gariepinus and Tilapia zilli. Of these, O.niloticus is the most dominant species. Meteorological data : Data on mean total monthly maximum and minimum air temperature, and monthly total rainfall of the lake region were obtained from Debre-Zeit Agricultural Research Center (Ethiopian Agricultural Research Institute) and are shown in Figure 2.
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Table 1: Some morphological, physical and chemical characteristics of Lake Babogaya (After d Prosser et al., 1968; c Zinabu Gebre-Mariam, 1994 ; b Yeshemebet Major, 2006)
Parameters Values Latitude 90N and 39 0Ed Altitude (m) 1870 d Surface area (Km 2) 0.58 d Volume (Km 3) 0.022 d Maximum depth (m) 71 b Mean depth (m) 38 d -1 c Conductivity,K 25 ( µscm ) 900 Alkalinity ( meq l -1 ) 10.2 b pH 9.2 b Salinity (gl -1 ) 0.9 b -1 b SiO-2 ( meq l ) < .1 Alkalinity (meq l -1) 10.80 b Na+ (meq l -1) 5.50 b Cl - (meq l -1) 0.90 b Sum of cations (meq l -1) 11.7 b Sum of anions (meq l -) 11.4 b
Mean monthly minimum air temperature ranged from 11.2 to 13.5 0C, while the maximum mean monthly air temperature varied from 21.6 to 31.5 0C. Monthly total rainfall varied from 2.1 mm (January 2006) to 239.5 mm (July 2006). Although the region was described by Baxter and Wood (1965) as having two rainy periods, the minor one extending roughly from February to April and the major one between June and September, appreciable quantities of rainfall were recorded throughout from February to August, 2006 including September, 2005, and peaking in July. Rippey and Wood (1985) also documented that the lake area has moderate rainfall, varying around about 850 mm per annum. The present meteorological data also show an annual mean rainfall of about 877.2 mm. Surface water temperature of the lake is reported to be mostly between 22 0C and 24.5 0C while the bottom temperature was almost constant (19.2 0C-19.4 0C) (Wood, et al. , 1976 and 1984). In a recent study (Yeshemebet Major, 2006), the water temperature and dissolved oxygen of the lake range from 23 0C to 27 0C and 7 mg l -1 to 14 mgl -1, respectively.
Materials and methods Capturing of fish and measurement : Specimens of O.niloticus were collected monthly between September 2005 and August 2006 using gill net. The gear (10 cm stretched mesh size) of 300 m long was set parallel to the vegetation. The gear was set in the afternoon (05:00 pm) and lifted in the following morning (7.00 am). Then immediately after capture, total length (TL) and total weight (TW) of sample fish were measured to the nearest 0.1 cm and 0.1g, respectively, and sexes of each specimen were determined by pressing the abdomen and/or dissecting the gonads. Determination of breeding season: The breeding season of O.niloticus was determined from the percentage of fish with mature gonads taken each month. The sexes of all fish and the maturity stages of the gonads were determined. The maturity level of each gonad was determined by visual examination using maturity keys. A five-point maturity scale was used for this purpose (Holden and Raitt, 1974) and all examined maturity stages were recorded for the determined GSI. Therefore, the breeding season of O.niloticus was determined based on the frequency of fish with ripe gonads and on Gonadosomatic index (GSI). The GSI for each fish was computed as the weight of the gonads as the percentage of the total body. GSI = (GW/TW) X100 Where, GW: Gonad weight in gram, TW: Total weight in gram
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300 40
250 30
200 Rainfall (mm) C 150 20 0 Mean min. Temp. 100 Mean max.Temp. Rainfall (mm) 10 Temp. 50 0 0 Sep - Oct Nov Dec Jan- Feb Mar Apr May Jun July Aug 05 06 Month
Fig. 2 . Monthly total rainfall, mean minimum and maximum air temperature of the Lake Babogaya region.
Fishing gear effort: In each month, yield of the fish were recorded in relation to the fishing gears. In addition to this the price that the fish were sold in all months were recorded for the analysis, and the products were transported to local markets. Revenue Fish production in the lake is mainly supplied for domestic markets. The average price of the fish in each month was calculated to assess cost variation across months. Therefore, the total revenue (TR) from the fish was calculated as price of fish multiplied by quantity harvested: TR = P * Y And profit was calculated as the difference of total revenue and cost incurred. PR = TR - C Where, TR - Total revenue P - Price Y - Yield PR - Profit C - Cost
Results and Discussion Composition of the fish: A total of 28,437 O. niloticus individuals were caught in all months. The total length of the fish ranged from 4 to 28 cm and the corresponding total weight ranged between 6 and 680 grams for both sexes. As shown in Fig. 2, the greater proportion of the sampled fish for both sexes ranged in size between 14 and 22 cm, with the peak being between 17 and 19 cm for the sexes. This length group alone was about 36% for females and 29% for males. Fish over 23 cm, and below 10 cm TL were least represented (Fig.3) Breeding season : Mean gonadosomatic index (GSI) ranged from 0.7 – 3.5 for females and from 0.6 - 2.1 for males. GSI values varied highly significantly between sampling periods for both sexes (ANOVA, P < 0.001). Temporal variation in GSI was remarkably similar between males and females (Fig. 4). Thus, there was a biannual cycle in which GSI increased from March peaking in April for females and June for males (Fig. 4). GSI values were lower between October to February.
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Fig. 3: Length-frequency distribution of O.niloticus in Lake Babogaya
4
3.5
3
2.5 Female 2 Male
Mean GSI Mean 1.5
1
0.5
0
6 n 05 Jul 0 Oct Dec 00 Feb Apr Ju Aug 2 Nov 2 Mar May p. n. Se Ja Month
Fig. 4: Temporal variation in gonadosomatic index (GSI) of O. niloticus from Lake Babogaya
The cycle in GSI was also reflected in monthly variation in the frequency of fish with ripe gonads (Fig. 4 and 5). The frequency was found to be high between April to August including September for both sexes (Fig. 5) which coincided with the periods of peak GSI values. In addition, lowest frequency of ripe fishes was recorded at times of lowest GSI values. Catch patterns of the fish: The dominant species in the catch was O.niloticus . The catch varied from month to month. Hence, high number of catch may be related to the amount of gears operated (Fig 6 and 7). Higher proportion of catch was conducted in January, March, April and August (Fig.7). This could show its high socio-economic importance, which might include consumption, employment and others. Fishing gears : A maximum of six gill nets and one timber boat were involved in fishing activities. The number of nets that were set was not constant. This is due to the demand of the fish in the local market. In March and April, the demand of the fish was high because this is the fasting period for Christians (Fig. 6). Therefore, to increase the amount of the fish, large sampling efforts were used.
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Fig. 5: Temporal variation in frequency (%) of ripe female and male O. niloticus from L. Babogaya
Fig. 6: Trend of effort (total boats and gill net) in Lake Babogaya.
Fig. 7 : Catch trend of the fish in Lake Babogaya
Even though the general trend of the catch seems to be increasing in relation to effort, it is hardly possible to predict the pattern. There fore, some research in relation to special and temporal abundance of the fish as well as stock assessment studies of the particular fish species for the lake must be conducted. 113 Ma nagement of shallow water bodies ..., EFASA 2010
Price of the fish: The catch was sold principally to local markets (restaurants and hotels) in Debre Zeit and Addis Ababa. Fish sold to retail outlets and to hotels/restaurants are usually filleted. The availability of high market outlet, which might be attributed to relatively good infrastructure and vicinity of the production area to the capital city, would have high probability of inviting more users to the fishery. The average price of the fish varied between 1.20 birr (February) and 2.89 birr (March) (Fig.8). This variation of price was related to the demand of the fish in the market. Demand was strongly linked to the fasting traditions of the Ethiopian Orthodox Church: most people consider that fish can be eaten on days when meat is not allowed (Wednesdays, Fridays and during the fasting months).
Fig. 8 : Average monthly price of fish in Lake Babogaya
Lake Babogaya is considered a rich source of fish, which generally does not yet show signs of over- fishing. Current instability in the production and marketing system suggests that the system itself is relatively competitive and exerting pressure on prices. Profits of the fishery : The total cost and profit analysis of the fishery for the lake were calculated from September (2005) to August (2006). The cost of the fishery included boat and gill nets rent, labours cost for fishing and processing and also transportation cost. Since the yield of the fish depend on the numbers of gill net, high yield were recorded in March (Fig 9 and Table). In addition to amount of gears, the numbers of days that operating the gears were also other factor (Fig.6).
Fig. 9 . Average cost, profit and revenue of the fish product
The costs for the fishery were dependent on the activity conducted. In March and April the cost were high, whereas in September, October and May, the costs were less (Table 3). This was because in March and April, the demand of the fish was high, hence it needed more costs to enhance the activity of fishery. The revenue of the product depended on the quantity of fish caught and the price of the fish in 114 Ma nagement of shallow water bodies ..., EFASA 2010 the market. Hence, in March and April there was high revenue of the product. The value was the least in September and increased from March and April. Then it decreased in May and increased again in August (Table 3 and Fig.9). The profit was also influenced by cost for the fishery activity and the product sold. Based on this, the results indicate that profit of the product is directly related to the revenue (Fig. 9 and Table 3).
Table 3. Cost, revenue and profit of capture fishery in Lake Babogaya.
Fish Cost (ET. Birr) Month Harvested Gill net Boat and Processing Transport Sub total Revenue Profit (Number) Labour fish cost September (2) 360 300 120 90 30 540 496.8 - 43.20 October (2) 500 300 120 125 30 575 690 115 November (5) 1440 500 300 360 40 1200 1987.20 787.20 December (5) 1560 500 300 390 45 1235 2152.8 917.80 January (10) 2000 500 600 500 150 1750 5500 3750 February (10) 1800 500 600 450 150 1700 2160 460 March (30 8575 800 1800 2143.75 450 5193.75 24781.75 19588 April (26) 6962 800 1560 1740.50 390 4490.50 19215.12 14724.62 May (2) 640 300 120 160 30 610 928 318 June (10) 1600 400 600 400 150 1550 3520 1970 July (10) 1200 400 600 300 150 1450 1680 230 August (10) 1800 800 600 450 150 2000 4698 2698 Total 28437 6100 7320 7109.25 1765 22294.25 67809.67 45515.42
Conclusion According to the results of this study, Lake Babogaya has biological potential to produce more fish but this might need detailed economical analysis to determine profitability. Maximum sustainable yield might be the most desirable equilibrium for a fishery in the absence of consideration of costs to harvest or discounting of future revenue from fishing. But fisheries management that may consider only biological factors might lose economic information, which could in turn have a valuable input and importance in management. The maximum sustainable yield of Lake Babogaya is unknown; hence, harvesting Lake Babogaya fishery with such knowledge may be a disaster for the lake. Therefore, there is need for such type of research for proper lake management and economic exploitation. To meet the objective of the profitability of fish markets, enhancing revenue or reducing the cost of production is a must. With all the limitations in place, this study might give an insight to the need of further investigation for better outcome in the status of the lake by making use of full data. Even though there was lack of maximum sustainable yield data for the lake, the study has indicated marginal profitability of the fishery in relation to other considered factors.
References Baxter, R. M. and Wood, R. B. (1965). Studies on stratification in the Bishoftu crater lakes. J. Appl. Ecol . 2: 416. Baxter, R. M. (2002). Lake morphometry and chemistry. In : Ethiopian Rift Valley lakes , Tudorancea, C. and Taylor, W.D. (eds.), pp. 45-60. Backhuys Publishers, Leiden, The Netherlands. EARO. 2002. NFLARRC. Baseline Survey Report on Current Status of Fisheries and Other Living aquatic Resources. FAO (1995). Review of the Fisheries and Aquaculture Sector. Ethiopia. FAO, Rome. Green, J. (1986). Zooplankton associations in some Ethiopian Crater lakes. Freshwat. Biol . 16 :495–499. Holden, M. J. and Raitt, D. F. S. (1974). Manual of fisheries science. Part 2.Methods of resource investigation and their application. FAO. Fish tech. 214 pp. Lamb, H.F. (2001). Multi-proxy records of Holocene Climate and Vegetation change from Ethiopian Crater Lakes. Institute of Geography and Earth Sciences, University of Wales Aberystwyth, Aberystwyth, http://www.ria.ie/cgi-bin/ria/papers . LFDP. 1998. Seventh Annual Progress Report, July 1997 to June 1998.
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Mohr, P. A. (1961). The geology, structure and origin of the Bishoftu explosion craters, Shoa, Ethiopia. Bull. Geophys. Obs., Addis Ababa , 2: 65-101. Prosser, M. V., Wood, R. B., and Baxter, R. M. (1968). The Bishoftu crater lakes: a bathymetric and chemical study. Arch. fur Hydrobiologia 65 :309-324. Rippey, B. and Wood, R. B. (1985). Trend in major ion composition of five Bishoftu crater Lakes. SINET : Ethiop.J .Sci . 8: 9-29. Tesfaye Wudneh, (1998). Biology and management of fish stocks in Bahir Dar Gulf, Lake Tana, Ethiopia. Ph.D. dissertation, Wageningen Agricultural University, Wageningen. 142 pp. Wood, R. B., Prosser, M. V. and Baxter, R. M. (1976). The seasonal pattern of thermal characteristics of four Bishoftu cater lakes, Ethiopia. Freshwat. Biol . 6: 519-530. Wood, R. B., Baxter, R. M. and Prosser, V. (1984). Seasonal and comparative aspects of chemical stratification in some tropical crater lakes, Ethiopia. Freshwat. Biol. 14 : 551-573. Wood, R. B. and Talling, J. F. (1988). Chemical and algal relationships in a salinity series of Ethiopian inland waters . Hydrobiologia 158 : 29- 67. Yeshimebet Major (2006).Temporal change in the community structure and photosynthetic production in Lake Babogaya, Ethiopia. M.Sc. thesis. School of Graduate Studies, Addis Ababa University, Addis Ababa. 79 pp. Zinabu Gebre-Mariam (1994). Long-term changes in indices of chemical and productivity status of a group of tropical Ethiopian lakes with differing exposure to human influence. Arch. Hydrobiologia 132 (1):115-125. Zinabu Gebre-Mariam (2002). The Ethiopian Rift Valley lakes: Major threats and strategies for conservation. In : Ethiopian Rift Valley lakes , Tudorancea, C. and Taylor, D.W. (eds.), p. 259-271, Backhuys Publishers, Leiden, The Netherlands. Zinabu Gebre-Mariam and Taylor, W.D. (1997). Bacteria-chlorophyll relationships in Ethiopian lakes of varying salinity: are soda lakes different? J. Plankton. Res. 19 : 647- 654.
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Part two Poster Session
A comparative study on the effect of three drying methods for better preservation of fish
Abera Degebassa, Ziway Fishery Research Center, P.O.Box 229, Zeway Tesfaye Alemu Aredo, Adami Tulu Agricultural Research Center, P. O. Box 35
ABSTRACT : Two experiments were conducted at Zeway Fishery Research Center (ZFRC) to test the effects of three drying methods and salting on moisture content of fish and hence their preserving efficiency. In the first experiment, salted fillets of both tilapia (Oreochremis niloticus) and catfish (Clarias garipienus) were subjected to three drying methods (rack, rock and solar) whereas in the second experiment, salted or unsalted fillets of tilapia were subjected to the three drying methods. Significant difference (p<0.05) in moisture content was observed among the fillets subjected to the three drying methods. Fillets dried in solar tent drier followed by those dried on rack had the lowest moisture content of 8 and 10.5%, respectively, for tilapia and catfish. Such fillets were also of good quality. Though salting as a main effect had no significant effect on moisture content of the fish, the salted fish in solar tent drier had significantly (p<0.05) lower moisture content than the unsalted fish in the same apparatus (8 vs. 10.8%). Iit was concluded that solar tent dryer and rack are appropriate and suitable for drying fish so that their shelf life can be prolonged.
Key words : Catfish, fish handling , fish drying, fish salting, fish preservation, Tilapia
Introduction Fish is an essential food resource. It supplies 25% of the total animal protein in developing countries (ICLARM, 1992); is the principal source of animal protein for over one billion people (Williams, 1996); and provides many important nutritional health benefits (Somerset and Bowerman, 1996; FRDC, 2001). Fisheries support livelihoods by providing employment and income to millions of people, both directly to those harvesting fish, and indirectly to those who supply materials, and who process and market the catch. Fish are also perishable food stuff. Spoilage occurs as a result of the action of enzymes and bacteria present on the fish and also due to chemical oxidation of fat which causes rancidity. At high temperature prevalent in tropical countries bacteria and enzymatic action are enhanced. Fish invariably become putrid within a few hours of capture unless they are preserved or processed in some way to reduce this microbial and autolytic activity and, hence, retard spoilage. Salting and drying are traditional methods of preserving fish that have been used for centuries. If the moisture content of fresh fish is reduced during drying to around 25%, bacteria can’t survive and autolytic activity will be reduced greatly. To prevent mold growth however, the moisture content must be reduced to 15% and below. The presence of salt retards bacterial action and removes water by osmosis (Waterman, 1976). Traditionally, many fishermen dry fish in open ground or on rocks in the sun. Some fish processors use mats or reeds laid on the ground to prevent contamination of the fish by dirt, mud and sand. Drying fish in this way has many problems and, in recent years, the uses of raised sloping drying racks have been introduced as a simple and effective technique (Clucas and Satcliffe, 1981). A cleaner product is obtained from rack drying since the fish do not come into contact with the ground. Also they are less accessible to domestic animals and pests such as mice, rats and crawling insects, which contaminate or consume them. Protection from rain is simply accomplished by covering the rack with a sheet of waterproof material (e.g. plastic). If fish on the ground are covered they are protected only from falling rain but not from water on the ground. When using racks drying rates are higher because air currents are stronger at a meter or so above the ground and air can pass under the fish as well as over them. The use of a slopping rack allows any exudates to drain away.
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However, even when racks are used, sun drying has many limitations: long periods of sunshine without rain are required; drying rates are low and in areas of high humidity, it is often difficult to get a uniform product. Thus, in search for improved drying techniques, the use of solar tent dryer has been investigated at Zeway Fishery Research Center as an alternative to traditional sun drying. Solar dryer employ some means of collecting or concentrating solar radiation with the result that higher temperature and lower relative humidity are achieved for drying. When using solar dryer, the drying rate is increased, moisture contents are reduced and product of higher quality than sun drying is obtained. The dryer is less susceptible to variations in weather. Although they do provide shelter from the rain , drying is slower during inclement weather.. The high internal temperature discourage the entry of pests into the dryer and can be lethal to any that enter also Thus, the main objective of the present study was to test fish preserving efficiency of salting and drying methods (solar tent, rack and rock drying) to prolong the shelf life of cured fish fillet .
Materials and methods Study area : This study was conducted at Zeway Fishery Research Center, 160 km South of Addis Ababa. The center is located in mid rift valley at an altitude of 1500 meter above sea level. The average annual rainfall of the area is about 688mm and its mean maximum and minimum temperatures are 27 and 14 oC, respectively. Its mean relative humidity and wind speed were recorded to be 55% and 1.66 m/second, respectively. Experiment and treatments : Two experiments were concurrently conducted to evaluate the efficiency of three drying methods and salting in preserving fish. In the first experiment, three methods of drying, namely, rack, rock and solar drying methods were tested using salted fillets of both tilapia and catfish. Photos of the three drying methods are shown in figures 1-3. In rack drying, the rack was constructed from locally available materials such as mesh wire, wood and nail. The rack was 1m above the ground, 1m wide and 1m long to protect the entrance of flies and other pests. During the rainy season it was covered with plastic sheet to protect the fish from the rain.
Fig 1 : Drying on racks Fig 2 : Drying on rocks
The solar dryer was constructed, using a wooden frame and plastic sheet. Black polythene was used for the base of the tent and clear ultra-violet resistant polyethylene for the sides and ends. Staples were used to attach the plastic sheet to the frames. The drying rack was built along one side of the tent using wooden frames and mesh wire. The principle of operation of the tent dryer is that the air inside the dryer is heated as it flows over the dark surfaces which absorb the heat of the sun resulting in air temperatures higher than that of ambient air. Upward flows of air takes place as air flows from the vents located at floor to those located at the top of the structured . The fish which are placed on wire racks are dried by the flow of air which gets progressively warmer as it rises upwards and leaves the structure by the top vents. According to Sazabo (1970), depending on the design of the solar dryer, temperatures of 70 oc and above can be achieved if there is no ventilation. The temperature can be lowered by opening the air vents thus allowing free movement of air.
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Fig 3 : Solar tent dryer
In the second experiment efficiency of the three drying methods was evaluated when used on either salted or unsalted fillets of tilapia fish. The treatments were arranged as 2X3 factorial with two levels of salting (salted or unsalted) and the above-mentioned three methods of drying methods. The treatment combinations were: • Drying salted fillet of tilapia on racks • Drying salted fillet of tilapia on rocks • Drying salted fillet of tilapia in solar tent dryer • Drying unsalted fillet of tilapia on racks • Drying unsalted fillet of tilapia on rocks • Drying unsalted fillet of tilapia in solar tent dryer In all cases two single fillets were removed from each fish and the fillets were washed and scored before they were put under drying. In case of salting, the fillets were packed in a dry salt (1kg salt for 5kg fish) for 12 hours. After salting, the fillets were carefully washed to remove excess salt crystals from the surface. Then they were allowed to drain before they were put in the drying treatments. Each treatment was replicated 5 times. In the case of rack and rock drying, the fillets were placed on the drying rack and rocks in the morning (9: 00 am) and removed in early evening (5:00 Pm). In order to ensure even drying the fillets were turned regularly 3 times a day. In the case of solar tent dryer, the drier was exposed to direct sun and it was heated prior to the start of the experiment. Vents and openings were closed early in the morning and late afternoon in order to raise internal temperatures as quickly as possible. Care was taken during the hottest periods of the day to maintain the internal temperatures between 48 oc-55 oc to avoid case hardening. In all the drying methods, the fish were placed in the driers in the morning and removed in early evening. Each batch of fish in the driers was weighed at 24 hours interval until it is completely dried after which it was allowed to cool, and then stored in plastic bags. Moisture content: Samples of all dried salted and unsalted products were analyzed for moisture contents. Moisture contents of 5gm dried fillets were determined relative to the weight of over-dried fish at 105 oC for 24 hours (Bostocketal, 1987). Chemical analysis: Chemical composition of salted and unsalted fish was analysed according to standard procedures. Dry matter, ash and Ether-extract were determined according to AOAC procedure (AOAC, 1990). Nitrogen (N) and phosphorus (P) contents were determined by auto analysis (Chemlab, 1978 and 1984) and Crude protein (CP) was calculated as N x 6.25. Calcium (Ca), potassium (K) and Magnesium (Mg) were analysed using atomic absorption spectorophotometer (Perkin Elmer, 1992).
Statistical analysis Effects of the three drying methods (rack, rock and solar) on moisture content of salted fillets of tilapia and catfish were analysed as CRD design. The effects of salting and drying methods were analysed as a
119 Ma nagement of shallow water bodies ..., EFASA 2010 factorial experiment with two levels of salting (salted and unsalted) and the three methods of drying using the GLM procedure of SAS (SAS, 2001).
Result and Discussion Chemical composition: Chemical composition of salted and unsalted fillets of the two fish species is shown in Table 1, Crude protein content of fillets of catfish ( Clarias gariepinus) was higher than that of tilapia ( Oreochromis niloticus) . This could be attributed to the difference in the feeding habits of the fish (Zenebe Tadesse et .al ., 1998). Clarias gariepinus are carnivores feeding on fish, insects and zooplankton. As food of animal origin contains more protein it is likely that tissue of fish feeding on such foods are of high protein.
Table 1 : Chemical composition of salted rack dried fillets of cat fish and tilapia
Fish type DM, % Ash OM N CP P EE CA Mg Cat fish 91.53 12.99 87.01 13.62 85.14 1.14 1.94 1.99 0.24 0.14 Tilapia 93.77 41.09 58.91 9.13 57.06 0.65 2.55 1.23 0.41 0.10
Effects of drying methods : The moisture content of salted rack dried fillets of tilapia and catfish is indicated in Table 2. For both type of fillets, solar drying resulted in lower (p<0.05) moisture content than the other two drying methods, and rock drying relatively yielded fillets of high moisture content. The average moisture content of solar dried fish were 8.0 and 10.5% for tilapia and cat fish, respectively, while that of the rock dried fish were 14.8 and 13.6%, respectively, for the two fish types . The water content of fresh fish is about 80%. If this is reduced to 25%, spoilage bacteria cannot survive as the lower moisture content inhibits growth of bacteria and molds. The result obtained from the current study showed that lower final moisture content than this critical value was achieved by using any of the drying methods. In rock drying the moisture content of tilapia fillet was higher than that of catfish fillet (Table 2). The reason was that the cut surface area of catfish fillet exposed to the air was increased and splitting decreased the thickness of the fish fillet. So drying of catfish fillet was faster and loss of moisture was higher than tilapia fillet. This technique was not done on tilapia fillet. In the other two drying methods, the moisture content of catfish fillet was higher than tilapia fillet, because catfish flesh is thick and cannot lose moisture as fast as tilapia fillet unless its surface area is increased.
Table 2 : Effect of drying methods on moisture content of salted fillets of tilapia and catfish Fish type Drying method Tilapia Cat fish Solar 8.00 c 10.52 b Rack 10.78 b 11.84 ab Rock 14.78 a 13.62 a ab = Means in a column with different superscripts are different (p<0.05)
Effects of salting and drying methods: As indicated in Table 3, the combined effects of salting and drying methods on moisture content of the fillets of fish was significant (p<0.05). Generally solar drying brought about lower moisture content of the fillet than any other drying method. However, the average moisture content of the solar dried salted fillet was significantly lower than that of the unsalted fillet with values of 8.0 and 10.8%, respectively. Therefore, salted solar dried fish has longer shelf life than unsalted fish and is less susceptible to spoilage caused by bacteria and molds. It was observed that drying salted and unsalted fillets of tilapia to the attained lower moisture content using the solar dryer required 3 days. This was due to the combined effect of the drier and the presence of salt in the fish.
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Table 3. Effect of salting and drying methods on moisture content of fillets of Tilapia Salting Drying method Moisture content (%) Salted tilapia Solar 8.0 d Rack 10.78 c Rock 14.78 a Unsalted tilapia Solar 10.76 c Rack 12.48 c Rock 13.76 ab ab = Means in a column with different superscripts are different (p<0.05)
For drying tilapia and catfish to the final moisture content of 20%, an acceptable figure for dry salted fish, the solar dryer required 60-65% of the time necessary for sun drying (3 days compared with 5 days). Under sunny condition, solar-dried fish would require 3 days to attain about 20% moisture. Fish on rack initially dried at faster rate but at lower moisture contents, their drying rates were lower than those on the rocks. A possible explanation for this might be that the initial higher rate could be due to the better air circulation around the rack, whereas in the final stages, the faster drying of fish spread on the rocks could be due to the higher air temperature surrounding the fish as a result of their proximity to the rocks. Comparison of the final dried products indicated that the solar dried fish were of good quality and were found to be marketable. Such fish was well dried with hard texture and pleasant odor. Sun dried products were of poorer quality, particularly than those fish dried on the rocks. They were contaminated with sand and dirt and the fish had suffered from attack by insects, birds and other animals. However, the sun dried products were of better quality than the locally produced dried salted fish which were well salted, but insufficiently dried and had very strong unpleasant odor. None of the experimental products showed any evidence of mold attack, ‘pinking’ caused by salt tolerant bacteria, beetle infestation, or case hardening. Scott (1957) reported that the stability of salted and dried food products depends on their water activity. This is a measure of free or available water in a food, which rest chemically or in spoilage, to support the growth of micro-organisms such as molds and bacteria (Waterman, 1976) For salted dried fish it is necessary to consider both the moisture content and the salt content when calculating water activity (Doe et al , 1982). A ration of high salt content has an inhibiting effect on growth of micro -organisms, except the red holophilic bacteria that are salt tolerant. The water activity of pure water is 1 and that of food is expressed as a fraction relative to that of pure water. Fresh fish have a water activity of about 0.95. Most spoilage bacteria cease to grow in a food whose water activity is below 0.90 and the growth of most molds is inhibited below 0.80. However, halophilic bacteria can grow at a water activity of 0.75 and some yerophilic molds as low as 0.65 (Bone, 1999). Both salting and drying have the effect of reducing water activity. During storage, dried fish flesh will absorb moisture from the air at higher humidity until equilibrium is reached. At humidity of above 75%, any salt in the fillet will also absorb moisture. Therefore, during storage, the product becomes wetter, thus increasing the water activity and it will become more susceptible to spoilage by molds and bacteria. Poulter et al . (1982) reported that fish treated with 20% salt and dried to 15% moisture content.d have mold free shelf life for 450 days. The present study also indicated that as the moisture content attained with salt content of 20% was less than 15%, the dried fillet can be stored for over one year with ut any spoilage. However, Sidwell et al., (1974) stated that for fish of high fat content such as catfish, the actual shelf life of the dried fish may be shorter due to the inevitable onset of rancidity. During the drying process and storage of the dried fish, infestation by insects is a major problem. This may cause additional losses in quality and quantity as insect pests are carriers of pathogenic bacteria and represent a serious health hazard (Proctor, 1977, Wood, 1981). Hence, care has to be taken at all storages of fish handling and processing in order to control insect infestation. As Proctor (1977) indicated though the primary effect of the salt is bactericidal, it can also retard insect infestation. This was evidenced by the current study where blowflies were found to be less attracted to the dry salted products compared to the unsalted fish.
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Conclusion and recommendation: The solar tent dryer and drying on rack produced a product of low moisture content that could have a long shelf life. Salting as such had no effect on moisture content of the fillets, though salted tilapia fillets had lower moisture content than the unsalted ones. Either tilapia or catfish dried in solar tent dryer or on rack under fine and sunny condition would dry in about 3 and 5 days, respectively, to achieve the final lower moisture content. Hence, it is recommended that solar tent dryer and rack are appropriate and suitable for small scale fishermen in Ethiopia as the energy from the sun is free, the drying time is short, the product is free from contamination by animals and the temperature is very high enough to kill flies and insects.
Acknowledgments The Ethiopian Science and Technology Commission and the Ethiopian Agricultural Research Institute are acknowledged for financial support.
References AOAC (Association of Analytical Chemists) (1990). Official method of analysis (15 th ed.). AOAC Inc. Arlington, Virginia, USA. AOAC (Association of Analytical Chemists) (1980). Official method of analysis (13 th ed.). AOAC Inc. Washington DC, USA. Bone, D.P (1993). Water activity- its chemistry and application. Food product development, 3 (15), 81-84. Bostock, T.W., Walked, D.J. and Wood C.D., (1987). Reduction of losses in cured fish in the tropics. Guide to extension workers. Chemlab. (1978). Continuous flow analysis. Method Sheet No. W2-075-01. Determination of Orthophosphate in water and waste water. Chemlab Instruments Ltd. Horn church, Esex, UK. Chemlab (1984). Continuous flow analysis system 40. Method Sheet No. CW2-008-17 (Ammonia (0-1 and 0-50 PPM. N). Chemlab Instruments Ltd. Horn church, Essex,UK. Clucas, I.J. and Sutcliffe, P.J. (1980). An introduction to fish handling and processing report of tropical products Institute, G143,86PP Clucas and AR Ward (1966). Post-Harvest Fisheries Development : A guide to handling preservation , processing and quality. Chatham Maritime, Kent ME4 4TB, United Kingdom Doe, P.E., Hashmi, R., Poulter, R.G. and Olley, 3, (1982). Isohalic Sorption isotherms 1. Determination for dried salted cod ( Gadus morrhua ). Journal of Food Technology , 17,125-134 Geoff Ames, Ivor clucas and susan, Scott panl, (1991). Post-harvest losses of fish in tropics. pp 1-22 FRDC.(2001).What is so healthy about sea food? Aguide about sea food marketers. Fisheries Research and Development Corporation, Australia 36p. ICLARM, (1992). ICLRAM,S strategy for International Research in Living Aquatic Resource Manegment ICLARM, Philipines.79p.and Apendez30p. Perkin Elmer (1982). Analytical methods for atomic absorption Spectrophotometer. Perkin Elmer Coorporation, Norwalk, Connenticut, USA. Poulter, R.G., Doe, P.E. and Olley, J. (1982) Isohalic sorption isotherms 2. Use in prediction of storage life of dried salted fish. Journal of food technology, 17,201-210 Proctor,D.L. 1997. The control of insect infestation of fish during processing and storage in the tropics. Processing of the conference on handling, processing, and marketing of tropical fish,pp.307_311.London Tropical Products Institute. Sazabo A., (1970). Rapport au Gouverment du malisur les ameliorations possible dl’utilization des produits de la peche. Repot FAO/UNDP (TA), (2900), Rome: FAO, 27pp Scott, W.J. (1957). Water relationships of food spoilage micro-organisms. Advances in Food Research, 7,83-127 Sidwell, V.D. , Foncannon,P.R. ,Moore...,N.S. and Bonnet, J.C. (1974). Composition of the edible portion of raw (fresh or frozen) Crustaceas, fin fish and molluscus.1. protein ,fat, moisture ,ash ,carbohydrate ,and colesterol. Marine Fisheries Review , 36 (3) , 21-35. Somorset, S. and M. Bowerman (1996). Enhanced usage of contemporary scientific finding on health benefits of sea food to promote fresh sea food consumption. Final report 1996/340. Fisheries Research and Development Corporation, Australia. 94p Waterman, J.J. (1976). The production of cured fish, FAO Fisheries technical paper No.166 Williams, M. (1996). The transition in the contribution of living aquatic resources to food security . Food ,Agricultural and the enviroment discussion paper 13.IFPRI, Washington D.C. Zenebe Tadesse, Ahlgren, G, Gustafsson, I-B and Boberg, M. (1998). Fatty acid and lipid content of Oreochromis niloticus L. in Ethiopia lakes: dietary effects of phytoplankton. Ecol. Fresh. Fish 7:146-158 122 Ma nagement of shallow water bodies ..., EFASA 2010
The effect of supplementary feeding on water quality during cage culture practice of Oreochromis niloticus in Lake Kuriftu, Ethiopia
Ashagrie Gibtan 1, Abebe Getahun and Seyoum Mengistou Department of Biology, Addis Ababa University, Addis Ababa, Ethiopia [email protected] 1
ABSTRACT: This research was conducted to investigate the effect of supplementary feeding on water quality during cage culture practice of Oreochromis niloticus in Lake Kuriftu, Ethiopia. Analysis of some physico- chemical parameters, zooplankton and phytoplankton were done for six months. The fish were fed a composite mixture of mill sweeping, cotton seed, and Bora food complex at 2% of their body weight twice per day using feeding trays in powdered form. The fish were grown in four treatments 50 (50F), 100 (100F), 150 (150F), and 200 (200F) fish per m 3. Samples were taken at two sites (site A- around the cage and site B- on the other side of the lake). The zooplankton abundance during the study period varied from 1.124 x 10 4 to 1.802 x 10 4 and from 1.156 x 10 4 to 2.118 x 10 4 individuals / m 3 at sites A and B, respectively. Abundance was almost the same at both sites. The highest value (2.118 x 10 4 individuals / m 3) was recorded at site B. At both sites, rotifers contributed most to the total abundance, followed by copepods and cladocerans. The result showed an insignificant difference in the abundance of zooplankton at the two sites (P < 0.05), but there was a significant difference in abundance between sampling dates (P > 0.05). Six phytoplankton groups were identified during the study period. The three taxonomic groups, blue greens, diatoms and greens, were dominant in the sense that they represented >90% of the total net phytoplankton. Relatively high proportion was observed at the beginning of the experiment and at the end of the experiment in both sites. There was significant variation (p > 0.05) in some physico-chemical parameters . However, this study indicated that overall, there was no significant effect of feed on water quality and plankton abundance in cage culture production in Lake Kuriftu.
Key words/phrases: Cage culture, Lake Kuriftu, Oreochromis niloticus , Water quality.
Introduction Freshwater bodies are finite resources essential for agriculture, industry, and human existence. For example, lakes are useful to humans in a number of ways, including their uses for industry, water supply, drinking and municipal water supply, commercial and recreational fisheries, river regulation, agricultural irrigation, navigation, body contact recreation, boating and other recreational uses. Nowadays, water quality of lakes is deteriorating due to both natural and anthropogenic effects. Agriculture, industries and urban settlements adjacent to or in the drainage basin of the lakes can further aggravate the deterioration of lakes’ water quality and human health problems by releasing contaminants, though the discharge of wastewaters into these water bodies or their sources waters. These effects may be more pronounced if the activities are done on the water bodies. Fish production in most of the water bodies of Ethiopia is far below the estimated yield and the pattern of production is by no means uniform; only capture fisheries. However, fish resources have been depleted from time to time (FAO, 1997). Therefore, the current increasing market demand for fish protein in Ethiopia can met only when the capture fishery is supplemented by aquaculture. The tilapine fishes especially, Oreochromis niloticus L., which have received considerable attention in many countries due to their good aquaculture potential, are widely distributed in Ethiopia. One of the reasons in which O. niloticus is selected for aquaculture is that it readily accepts artificial feeds . In cage culture practice, there is use of different supplementary feeds. The supplementary feeds used in tilapia culture employed in Asia and Africa includes rice bran, broken rice, oil cakes, flour, corn meal, kitchen refuse, rotten fruit, coffee pulp, and a variety of aquatic and terrestrial plants (Diana et al ., 2004). The use of this supplementary feeds cause water quality deterioration. Therefore, water quality management is a key ingredient in a successful operation including aquaculture (farming of aquatic organisms). Such caution is even important to avoid poor growth, disease and parasite outbreaks, and fish kills which can be traced to water quality problems. Water quality management is undoubtedly one of the most difficult problems facing the fish farmer. Water quality problems are even more difficult to predict and to manage. A more thorough study on water quality problems should be addressed to solve such problems . Therefore, the purpose of this study 123 Ma nagement of shallow water bodies ..., EFASA 2010 was to evaluate the effects of supplementary feeding on the water quality of the lake during cage culture practice of Nile tilapia ( Oreochromis niloticus ) in Lake Kuriftu, Ethiopia. Study site and experimental design: The study was conducted in Lake Kuriftu (Fig.1), Ethiopia, at an altitude of 1860m, some 47 km southeast of Addis Ababa. The lake is located at 8 047 'N and 39 010'E. It is a shallow (6m) artificial lake formed by diverting and damming Belbela River (Kebede et al. , 2001). It has an area of 0.4 km 2, a volume (m 3) 3.0 x 10 6. T-shaped jetty was constructed in the lake with a total length of 25m: 15m into the water and 10m side ways. Two sites (Fig.1), one in the cage area (designated as site A) and the second on the other side of the shore (designated as site B), were chosen for physico-chemical parameters, phytoplankton and zooplankton sampling and assessment. The cages were constructed with a size of 1m 3 (1m x 1m x 1m) from PVC material (frame) and an enclosure of nylon netting material. The PVC was type 50, with a tube of 10 cm with 1mm polyethylene material. The net mesh had 4 cm stretch length. The cages were placed in the constructed jetty side by side in rows at 1m intervals. O. niloticus juveniles of mixed sex were collected from Lake Babogaya using beach seine hauls 50m x 2.5m (with stretched mesh size of 20mm). Fish were stocked in combinations of 50 juveniles x 2 cages, 100 juveniles x 2 cages, 150 juveniles x 2 cages, and 200 juveniles x 2 cages on 5 January, 2007 and left for 5 days to acclimatize. The cages with different stocking densities were coded as 50F, 100F, 150Fand 200F, where F refers to feeding. The fish in these cages were feed 2 % of their body weight two times (early morning at 8:00 am and late afternoon at 4:00 pm) per day in powdered form using feeding trays. The proximate composition of ingredients used in the preparation of diets for feeding consist of mill sweeping (60 %), cottonseed (10 %), Bora food complex (30 %) (Table 1). The stocks had free access to the natural foods. Feeding rate tables were adjusted every two weeks based on the average weight of fish. Feed was offered to the caged fish only at 2 % of the body weight for the feed treatments as described in Chapman (2006), except for the controls where fish fed directly in the natural environment only .
5
Fig. 1 . Lake Kuriftu with sampling sites (enlarged image). The inset in the map of Ethiopia represents the Bishoftu Crater lake area. Table 1 . Feed types and their nutritional composition. Feed type % carbohydrate % fat % protein % fiber Reference Mill sweeping 58.0 14.0 12.5 7.5 Bardach et al., 1972 Cotton seed 29.6 18.8 22.8 24.1 Bardach et al., 1972 Bora food complex 35.0 8.8 35.0 20.0 Pers. Com.
Data collection : The meteorological data of the lake region during the study year were obtained from National Meteorological Service of Ethiopia (NMSE). Water temperature was measured with thermometer in situ monthly (from January to June, 2007) at 25 cm below the surface at Sites A and B. 124 Ma nagement of shallow water bodies ..., EFASA 2010
Visibility was measured monthly at 12:00 am using Secchi disk at both sites. Visibility was calculated as the average depth at which the Secchi disk disappeared when lowered, and the depth at which it reappeared when raised (Boyd, 1990). The secchi disk depth was used to estimate the euphotic depth of the lake. Similarly, pH was measured with pH meter. To estimate zooplankton abundance in the experimental lake, water was collected at 2 m depth at the two sites (A and B) starting from January to June, 2007. Zooplankton samples were collected with a net mesh size of 67 µm and diameter of 31 cm. The samples were immediately preserved in 5 % formalin. The volume of the water filtered through the net was determined by using the formula (V = 3.14 r 2h) where, r is the radius of the net mouth and h is the depth from which the sample was taken. Based on this, the number of organisms per m 3 of the lake was calculated and then the number of each category of zooplankton of the lake was expressed as per m 3. 20 - 25 ml of sub-sample was taken for counting using pipette with wide mouth and poured into a gridded petri dish. Three grids were counted for each sample after allowing the sample to settle and checking the uniform distribution throughout the grids and then extrapolation was made. Counting was done with stereoscope microscope (magnification of 50 x) and the zooplankton species were identified using keys in Fernando (2002). Samples for estimation of the relative abundance of the different taxonomic groups of the phytoplankton community were collected with plankton net of 10 µm mesh size at 2 m depth of the open water in Sites A and B. The samples were stored in brown bottles preserved using Lugol’s solution (Wetzel and Likens, 2000) and placed in a refrigerator. The samples were examined with inverted microscope and the identification of phytoplankton to genus or species level was made using different identification keys including those of Whitford and Schumacher (1973); Talling (1987); and Willen (1991). Aliquots of the preserved samples were used, after sedimentation, for the estimation of the relative abundance of the major algal groups with Sedgewick – Rafter cell under an inverted microscope (Nikon) following the procedures outlined in Hotzel and Croome (1999). According to Hotzel and Croome (1999), the number N x 1000 M 3 of cell per ml was calculated as Co = where N is the number of cells, A is the area of A x D x F x 10 1 field (mm 2), D is the depth of field (mm), and F is the number of fields counted and is the 10 concentration factor. The fish length (using measuring board) and weight (using Ohaus portable balance) were measured and recorded at two weeks interval. At the end of the experiment, the fish were harvested and weight and length of all fish were measured. Data analysis: To check the variation in physico-chemical parameters, zooplankton and phytoplankton abundance between Sites A and B, statistical test (ANOVA) was used. These analyses were done using SPSS (1999) and Minitab (Version 14) (2003). All statistical tests were considered significant at p < 0.05 as indicated in Sokal and Rohlf (1995). Growth performances of fish were determined and feed utilizations were calculated as:
Weight gain (gm) = Final weight (gm ) − Initial weight (gm ) .
Results and Discussion Results: According to the data of NMSE, this is plotted in Figure 2, mean monthly minimum air temperature ranged from 3.5 to 13.8 oC, while the maximum monthly air temperature varied from 24.0 to 28.4 oC. Monthly total rainfall varied from 2.9 mm (November 2006) to 186.7 mm (August 2006) (Fig. 3). Surface water temperature of the lake is reported to be between 20 oC and 27.4 oC (this study) while the bottom temperature was almost constant (19.2 oC to 19.3 oC) (Rippey and Wood, 1985).
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30
25
20 Maximum 15 Minimum 10
5 Temperature (oC) oC) (oC) Temperature 0 6 6 6 6 7 7 007 200 , 2006 , 200 R, 2007 JUL, JUNE, 2006 AUG, 200SEP, 200OCT, 200NOV, DEC2006 JAN, 2OO7FEB, 2MA APR, 200MAY Months
Fig. 2 : Mean monthly air temperature at Lake Kuriftu area (Source: NMSE).
Fig. 3 : Mean monthly rainfall at Lake Kuriftu area (Source: NMSE).
Physical parameters including water temperature, Secchi disk transparency and the chemical parameter (pH) measured at monthly interval for a period of six months are summarized in Table 2. In Site A, the water temperature ranged from 20.6 oC to 27.6 oC while in Site B it was 21.5 oC to 27.5 oC. pH and Secchi depth ranged from 8.32 to 8.78 and 35 to 60 cm for Site A and 8.33 to 8.81 and 31 to 58 cm for Site B. The water temperature was relatively high during May and June, medium in January, March and April and relatively very low in February in both sites (Fig. 4). The physico-chemical parameters were fairly the same in the two stations (Sites A and B) during the experimental period. They were not significantly affected by culture conditions (P > 0.05), but were affected by experimental dates alone (P < 0.05).
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Table 2 . Some physico-chemical parameters in the two sites (A and B) in Lake Kuriftu during the study period.
Station Sampling dates Parameters Site A Site B January 9, 2007 Water temperature ( O C) 25.3 25.1 pH 8.44 8.41 Secchi depth (cm) 53 51 Euphotic depth (cm) 159 153 February 9, 2007 Water temperature ( O C) 20.6 21.5 pH 8.78 8.81 Secchi depth (cm) 52 50 Euphotic depth (cm) 156 150 March 9, 2007 Water temperature ( O C) 22.7 22.7 pH 8.45 8.42 Secchi depth (cm) 60 59 Euphotic depth (cm) 180 177 O April 10, 2007 Water temperature ( C) 24.1 24.0 pH 8.32 8.33
Secchi depth (cm) 55 53 Euphotic depth (cm) 165 159 May 9, 2007 Water temperature ( O C) 27.4 27.5 pH 8.6 8.7 Secchi depth (cm) 58 58 Euphotic depth (cm) 174 174 June 10, 2007 Water temperature ( O C) 26.3 26.4 pH 8.51 8.49 Secchi depth (cm) 35 36 Euphotic depth (cm) 105 108
30
25
20 Site A 15 Site B 10
Temperature in oC 5
0
. 9 b.9 . 9 10 . 9 10 an e ar r. ay n. J F M Ap M Ju Sampling Date
Fig. 4 . Water temperature records of Lake Kuriftu at sites A and B from January 9, 2007 to June 10, 2007.
Zooplankton abundance during the study period varied from 1.124 x 10 4 to 1.802 x 10 4 and 1.156 x 10 4 to 2.118 x 10 4 individuals per m 3 at Sites A and B, respectively (Fig.5). Abundance was almost the same at both sites. The highest value (2.118 x 10 4 individuals per m 3) was recorded at Site B. In both sites, the highest value was attained in January and February 2007 and densities started to decline in April and
127 Ma nagement of shallow water bodies ..., EFASA 2010 later increased in June (Fig. 5). The temporal variation of total zooplankton abundance for each site is depicted in Figure 5. At both sites, rotifers contributed more to the total abundance followed by copepods and the cladocerans contributed the least to the total abundance. The number of the cladocerans, copepods and rotifers during the study period were 1.242 x 10 4 individuals / m 3, 2.486 x 10 4 individuals / m 3, 4.392 x 10 4 individuals / m 3 in Site A and 1.282 x 10 4 individuals / m 3, 2.636 x 10 4 individuals / m 3, 4.620 x 10 4 individuals / m 3 in Site B, respectively. Analysis of variance (one-way ANOVA) was performed for the two sites. There was no significant difference in the abundance of zooplankton at the two sites (P > 0.05), but there was a significant difference in abundance between sampling dates (P < 0.05).
14000 12000 Copepod A Copepod B 10000 Cladoceran A 8000 Cladoceran B 6000 Rotifer A 4000 Rotifer B 2000 Individual number / litter / number Individual 0
7 7 7 7 7 7 -0 -0 -0 -0 -0 -0 n b ar pr y n Ja Fe M A Ma Ju Sampling date
Fig. 5 . Zooplankton abundance in Lake Kuriftu (individuals / m 3) at the two sites.
Table 3 . Zooplankton taxa identified from Lake Kuriftu during this study.
Copepoda Cladocera Rotifera Mesocyclops aequatorialis a Ceriodaphnia sp. Asplanchna sp. a Thermocyclops consimilis ++ Diaphanosoma excisum Brachionus bidentata B. calycyflorus Moina micrura B. caudatus B. falcatus ++ Filinia sp. a Keratella sp. a ++ Dominant species; ª Rare occurrence
The list of species of phytoplankton recorded for Lake Kuriftu is presented in Table 5. Six phytoplankton groups were identified during the study period. The number of phytoplankton cells, colonies and filaments are given in percentage in Table 4. The three taxonomic groups, blue greens, diatoms, and greens were dominant in the sense that they represented > 90 % of the total net phytoplankton. At Site A, 60 - 85 % of the total phytoplankton was represented by Cyanobacteria. They were 67 - 91 % in Site B during the study period. The contribution of the green algae never exceeded more than 29 % of the total phytoplankton in the two sites. A relative high proportion was observed at the beginning of the experiment and at the end of the experiment in both sites. Blue green algae were the most dominant in almost all the months in both sites.
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Table 4 . Percentage (%) composition of phytoplankton in Lake Kuriftu.
Cyanophyceae Chlorophyceae Bacillariophyceae Others Sampling date Site A Site B Site A Site B Site A Site B Site A Site B January 9, 2007 85 91 13 3 1 2 3 4 February 9, 2007 70 74 26 21 2 2 2 3 March 9, 2007 60 67 29 20 10 12 1 1 April 10, 2007 70 71 20 18 9 10 1 1 May 9, 2007 71 73 16 12 11 13 2 2 June 10, 2007 70 77 20 13 8 9 2 1 Total 71.0 75.5 20.67 14.5 6.83 8.0 1.83 2.0
Table 5 . List of phytoplankton identified from Lake Kuriftu.
Phytoplankton group Species name Cyanophyceae (Cyanobacteria) Anabaena circinalis + Chroococcos sp. Cylindrospermopsis africana ++ C. Curvispora ++ Microcystis aeuroginesa ++ Psuedoanabaena sp. Chlorophyceae Chlamydomonas reticula (Green algae) Closterium species Pediastrum simplex P. duplex Phacotus lenticularis Scenedesmus armatus Bacillariophyceae (Diatoms) Navicula cryptocephale Nitzschia vernicularis N. rostellate Synedra sp. Dinophyceae (Dinoflagellates) Peridinium sp n. Cryptophyceae (Cryptophyta) Cryptomonas sp. Euglenophyceae (Euglinophyta) Lepocincilis sp. Phacus sp ⁿ. ++ most dominant, + dominant, ⁿ rare occurrence
The highest weight (219.71 gm) of O. niloticus was attained at a density of 50 fish / m 3 with supplementary feeding followed by 100 fish / m 3, 150 fish / m 3, 200 fish / m 3 (Fig.6). The lowest weight (116.42 gm) was obtained at a density of 50 fish / m 3 without supplementary feeding (Fig. 6). The data were tested at 95 % confidence interval and their growths were significantly affected by stocking density and supplementary feeding (P < 0.05).
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250
200 50N 150 50F 100F 100 150F
Weight in gm in Weight 200F 50
0
9 4 5 2 2 10 b. un n. r. -May -J Fe eb. 9 Ja Jan.25 F 10-MarMa Apr. 10 Apr. 25 10 25-May Sampling dates
Fig. 6 . Temporal variation in mean weight of fish in the five treatments.
Discussion In both experimental sites, the different physico-chemical parameters of the water were close to each other and were within the safe limits. No significant difference in physical parameters was detected between the sites. These parameters (pH, temperature, and secchi disc transparency), measured during the study remained in the favorable range for O. niloticus (Boyd, 1990; Gibtan et al ., 2008), suggesting that O. niloticus growth performance was not limited by any of these parameters except temperature which was low record during February. This is in agreement with Diana et al . (1996) who emphasized that the efficient use of supplementary feed at a limited rate, along with natural feeds does not adversely affect water quality. The results found in the two sites indicate that there wass no significant difference in abundance of zooplankton between the sites (Table 3). Rotifers were the most abundant in both sites followed by copepods and cladocerans. This is in agreement with the recent study of Tamire (2006) who reported that the lake zooplankton community was dominated by rotifers followed by copepods and cladocerans. Since there is no significant variation between sites, the experiment did not bring any adverse effect on the lake zooplankton abundance. This is further supported by the feeding behavior of Nile tilapia ( O. niloticus ). O. niloticus ingestion rate of zooplankton decreased with increasing fish total length (Moriarty and Moriarty, 1973). Temporary changes in percentage contribution of the different algal groups to the total abundance of the phytoplankton community in Lake Kuriftu were observed, although the blue-greens were the most abundant in the study period. The blue-greens accounted for over 60 % of the total phytoplankton abundance. However, the phytoplankton communities were dominated by green algae during the study done by Lemma (1997). This variation might be due to the variation in the length of sampling time. Among the blue greens, Microcystis were the most important contribution to the total phytoplankton abundance in this study. Microcystis are among the troublesome alga genera that commonly form blooms in lakes (Boyd, 1990). The formation of such algal blooms might be initiated and enhanced by one or several environmental factors such as light, temperature and availability of nutrient in the open water, although the relative importance of these factors vary considerably among different phytoplankton species (Reynolds, 1990). However, the formation of blooms due to the added supplementary feeding might be low as the foods put in suspended feeding trays retained feed floating and prevented wastage and were consumed by fish.
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Moreover, there is no significant variation between sites; the experiment did not bring any adverse effect on the lake phytoplankton abundance. This is further supported by high productivity of the lake (Tamire, 2006). However, further study should be done to investigate the effects on the phytoplankton community under intensive practice. Physical, chemical and biological parameters are the same among cages or between cages and the open water in the present experiment. Thus, all O. niloticus had similar culture environment and equal access to natural foods. The feed intake observed is only a function of the Tilapia ( O. niloticus ) group and the individual physiological condition of the fish; body mass of each individual changed as a function of feed intake and feed conversion efficiency. Compared to nonfeeding cages, the addition of supplemental feed resulted in significantly higher growth. The growth differential between nonfed and fed tilapia (O. niloticus ) started during the first two weeks of culture (Fig. 6). Similar results were reported for Nile tilapia (O. niloticus ) cultured in fresh waters (Diana et al ., 1994). However, Moav et al . (1977) did not find a significant difference in growth of cultured fish with and without supplemental feeding, which was likely due to lower densities of stocked fish (Diana et al ., 1994). Moreover, Watanabe et al. (1990) showed that, the growth of Florida red tilapia that were fed supplementary feed did not differ at densities ranging from 100 to 300 / m 3, which was due to intensive culturing condition. The results of this study showed that under the present conditions (feed type, feeding frequency), the supplemental feed provided could make a substantial contribution to the growth of this species. Clearly, the fish analyzed in the feeding treatment (50F) of the same stocking density did not even come close to growth encountered when kept without food (50N). It is possible to confirm that addition of feed in present proportion (2 % per body weight of fish), twice a day, brought a substantial growth difference. However, different feeding regime involving more frequent feed applications must be studied. In view of this, the used supplemental feed for O. niloticus in Lake Kuriftu should be reviewed critically, partly from the aspect of availability of food but also from a cost-benefit point of view. Therefore, study measures should be taken to improve this. These need not be based on a ban on the use of feed but could also rely on distinct improvements in the culture methods and techniques like use of supplied feed in pelleted form, frequency of feeding, quality of feeding, demand feeding regime (automatic feeders) which were not included in this experiment. This would allow a reduction in supplementation levels, making culture cheaper, as well as minimizing eutrophication from wasted feed. Regardless of the supplementation levels and the way of supply used (with feeding tray) in the present study, the fed cages with low stocking density gained higher weight than those with higher stocking density .
Conclusions and recommendations This study on cage aquaculture is one of the first two in Ethiopia. The other concurrent study was that of Abebe Tadesse (see reference) in Lake Elen who obtained results similar to those obtained in the present study. Needless to say, much more research is required on cage culture in Ethiopia. Investigations on other water bodies like reservoirs, dams, rivers should also be conducted. In addition, similar studies using other production systems, such as pond, pen and tank, should be conducted and compared with cage culture. Furthermore, other aspects of cage aquaculture, for instance cage size and type as well as economic feasibility should be investigated . In this study, no adverse effect of the experiment on the lake plankton abundance was observed; this needs to be studied when the cage culture is intensive. In addition, effect of cage culture on the lake nutrient loading, macrophytes, littoral and benthos community needs profound investigation. The best stocking density with regard to growth performance, condition and feed conversion efficiency was 50 fish / m 3 of cage .
Acknowledgments We are grateful to all members of Kale Hiwot Church at Lake Kuriftu, Sebeta National Fishery and Other Aquatic Life Research Center and Ziway Fisheries Resource Center who collaborated in different ways while we were conducting our experiment. We thank the Systematic Research Fund of the America Museum of Natural History and Development Innovation Fund of the Zoological Natural History Museumof the Addis Ababa University. 131 Ma nagement of shallow water bodies ..., EFASA 2010
References Bardach, E.; Ryther, H. and Mc Larney, O. (1972 ). Aquaculture: The Farming and Husbandry of Fresh Water and Marine Organisms. John Wiley and Son. New York. 47 - 37pp. Boyd, C. (1990). Water Quality in Ponds for Aquaculture . Alabama Agriculture Experiment Station. Auburn University. Alabama. USA. Chapman, F. (2006). Culture of Hybrid Tilapia: A Reference Profile . University of Florida. Institution of Food and Agriculture Science. USA. Diana, J.; Lin, C. and Jaiyen, K. (1994). Supplemental feeding of tilapia in fertilized ponds. Journal of the World Aquaculture Society . 25: 497 - 506. Diana, J.; Lin, C. and Yi, Y. (1996). Timing of supplemental feeding for tilapia production . Journal of the World Aquaculture Society. 27 : 410 - 419. Diana, J.; Yi, Y. and Lin, C. (2004). Stocking densities and fertilization regimes for Nile tilapia ( Oreochromis niloticus ) production in ponds with supplemental feeding. In : Proceedings of the 6 th International Symposium on Tilapia in Aquaculture , 487 - 499 pp. (Bolivar, R.; Mair, G. and Fitzsimmons, K. eds.). Manila. Philippines. FAO (1997). Fisheries Management . No. 4 . Rome. FAO. Fernando, C. (2002). A Guide to Tropical Freshwater Zooplankton: Identification, Ecology and Impact on Fisheries . Backhuys Publisher. Leiden. Netherlands. 291 pp. Gibtan, A.; Getahun, A. and Seyoum M. (2008). Effect of stocking density on the growth performance and yield of Nile tilapia [ Oreochromis niloticus (L., 1758)] in a cage culture system in Lake Kuriftu, Ethiopia. Aquaculture Research . 39 : 1450 -1460. Hotzel, G. and Croome, R. (1999). A phytoplankton Methods Manual for Australian Freshwaters . Land and Water Resource Research Development Corporation. Canberra. Australia. 51pp. Kebede, S.; Ayanew, T. and Umer, M. (2001). Application of isotope and water balance approaches for the study of hydrogeological regime of the Bishoftu crater lakes, Ethiopian. SINET: Ethiopian Journal of Science. 24: 151 - 166. Lemma (1997). Der Einfluß zooplanktonfessender Fische auf die Größenfraktionen des phytoplanktons und die primärproduktion in gemäßigten und tropischen Seen. Ph D. Thesis. Technische Universität. Dresden. Germany. 199pp. MINITAB (2003). Version 14 . Minitab Inc. USA. Moav, R.; Wohlfarth, G.; Schroeder, G.; Hulata, G. and Barash, H. (1977) . Intensive polyculture of fish in freshwater ponds: substitution of expensive feeds by liquid cow manure. Aquaculture. 10 : 25 - 43. Moriarty, C. and Moriarty, D. (1973). Quantitative estimation of the daily ingestion of phytoplankton by Tilapia nilotica and Haplochromis nSGRipinnis in Lake George, Uganda. J. Zool. Lond. 171: 15-23. National Meteorological Services of Ethiopia (NMSE). 2006 / 2007 Meteorological data of Bishoftu Town. Reynolds, C. (1990). Temporal Scales Variability in Pelagic Environments and the response of Phytoplankton. Freshwater Biology . 23 : 25 - 53. Rippey, B. and Wood, R. (1985). Trends in major ion composition of the five Bishoftu crater Lakes. SINET: Ethiopia Journal of Science. 8: 9 - 29. Sokal, R. and Rohlf, F. (1995). Biometry. 3rd Edition. W.H. Freeman and Co. New York. USA. 887 pp. SPSS (1999). Software Program of Statistical Analysis . Version 8.0 Edition for Windows. SPSS Inc .Chicago. USA. Tadesse, A. (unpublished). The effect of stocking density and supplementary feeding on growth performance of Nile tilapia [ Oreochromis niloticus (L., 1758)] in cage culture system in Lake Elen, Ethiopia. Talling, J. (1987). The phytoplankton of Lake Victoria (East Africa). Arch. Hydrobiol. Beih. Ergebn. Limnol. 25 : 229 - 256. Tamire (2006). Zooplankton community grazing rates on the natural phytoplankton assemblage in Lake Kuriftu. M. Sc. Thesis. Addis Ababa University. Ethiopia. Watanabe, W.; Clark, J.; Dunham, J.; Wicklund, R.; and Olla, B. (1990). Culture of Florida red tilapia in marine cages: effect of stocking density and dietary protein on growth. Aquaculture . 90 : 123-134. Wetzel, R. and Likens, G. (2000). Limnological Analysis . 3 rd ed. Springer-Verlag. New York. USA. Whitford, L. and Schumacher, G. (1973). A Manual of Freshwater Algae. Sparks Press. Raleigh. N.C. 323 pp. Willen, E. (1991). Planktonic diatoms-an ecological review. Algological Studies . 62 : 69 - 106.
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Growth of Labeobarbus spp. in aquaria and pond conditions
Belay Abdissa: Bahir-Dar Fishery and Other Aquatic Life Research Center [email protected], F.N. Shkil, K.F. Dzerzhiskii, Wondie Zelalem, Mesfin Tsegaw: Joint Ethio- Russian Biological Expedition (JERBE III)
ABSTRACT : Lake Tana (Ethiopia) is inhabited by large African barbs (Barbus intermedius complex sensu Banister, 1973) differing in morphology in such a degree that up to 15 distinct species forming the species flock were distinguished (Nagelkerke and Sibbing, 2000). Given its wide diversity, this species flock is considered to be unique among cyprinids. Consequently, Lake Tana is often considered as a natural laboratory to study the evolutionary process in fish. On the other hand, the large Lake Tana barbs are commercially valuable species. The commercial fishery at the lake began to develop intensively beginning from 1980 when the motorized boats and nylon gillnets were introduced. Now the main pressure on the stock of large Lake Tana barbs falls during the spawning season. The fishery activity focuses on the mouth of the rivers where the large barbs spawn, resulting in the decrease of the large barbs diversity and of the density of barbs population. Also, the damming of the rivers feeding the lake for irrigation and electric power project leads to changes of their hydrographic regime and to the disappearance of the large barbs spawning sites. Combined, these factors make large barbs of Tana lake an endangered species. To save the unique large barbs species flock valuable both for science and commercial fishery, one needs to create the restoration fish stock. For this aim, JERBE III developed methods of artificial breeding and further rearing of large barbs under artificial conditions. During the last 5 years we obtained progeny from different species of large Lake Tana barbs and succeeded to grow them up till their sexual maturity. As a result, artificial fish stock of endangered Lake Tana barbs was created in the Bahir-Dar Fishery and Other Aquatic Life Research Center. These positive results indicate the necessity to continue this project.
Key words/phrases : Artificial condition, Breeding, Labeobarbus, Lake Tana.
Introduction With the extinction of most of the endemic cyprinid species in Lake Lanao in the Philippines (Kornfield and Carpenter, 1984), the Labeobarbus species of Lake Tana ‘Ethiopia’ form, as far as is known, are the only remaining intact species flock of ‘large’ cyprinid fishes left in the world (Nagelkerke et al., 1994; Nagelkerke and Sibbing, 2000). Lake Tana (Ethiopia) is inhabited by large African barbs differing in morphology in such a degree that up to 15 distinct species forming the species flock were distinguished (Nagelkerkeand Sibbing, 2000). Given its wide diversity, this species flock is considered to be unique among cyprinids. Consequently, Lake Tana is often considered as a natural laboratory to study the evolutionary process in fish. On the other hand, the large Lake Tana barbs are commercially valuable species. The commercial fishery at the lake began to develop intensively beginning from 1980 when the motorized boats and nylon gillnets were introduced. Now the main pressure on the stock of large Lake Tana barbs falls during the spawning season. The fishery activity focuses on the mouth of the rivers where the large barbs spawn resulting in the decrease of the large barbs diversity and of the density of barbs population (data of Bahir-Dar Fishery andandOther Aquatic Life Research Center) (Fig.1). Also, the damming of the rivers feeding the lake for irrigation and electric power project leads to changes of their hydrographic regime and to the disappearance of the large barbs spawning sites. Combined, these factors make large barbs of Tana lake endangered species .
Materials and methods Field observations were carried out in September and October 2005 at the Gumara River and its tributary, the Ducalit (Fig. 2), near the village of Wanzaye (Hot Springs).For this aim, Bahir-Dar Fishery Research Center and JERBE III developed the methods of artificial breeding and further rearing of large barbs under artificial conditions using indoor aquaria system and concrete tank build at the Bahir Dar Fisheries and Other Aquatic Life Research Center. The fish were sampled with cast nets of 3.2 m in diameter when open. Having noticed an aggregation of spawning barbs, we collected them with cast nets.Splashes produced by the female’s tail movements were the main noticeable sign of the spawning.
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For artificial fertilization we used eggs and sperm obtained from running barbs caught in the Dukalit mouth.
Fig.1 . Catch Per Unit Effort (CPUE) of Lake Tana large Barbus (2000-2004)
Fig.2. Dukalit stream of Gumara River
We obtained the eggs of large barbs by artificial fertilization (“dry method” in Petri dishes) from the wild parents caught in the Lake Tana tributary the Gumara River at the spawning season (the end of the rainy season September/October). The capture of the parents was carried out by the cast-net. The use of cast-net gives the opportunity to reduce the damage of fish and avoid the premature loss of eggs and sperm by squeezingThe ripe running females were wiped with dry tissue and positioned over the Petri dish. The anal fin has to be directed to the center of Petri dish. Then, the smooth pressing of female abdomen direct from the head to the anal fin released the eggs which were squeezed out to the bottom of the petri dish. We captured sperm from males in the same manner and positionede it at the side at the same petri dish. Immediately, the eggs and sperm were mixed well witha feather and the Petri dish was placed into the running shallow water (Fig.3). The eggs show stickiness after fertilization for a short time. Therefore, it’ was necessary to wait until the eggs became unstuck and begin to float. Further, the eggs may be transferred to the plastic bottle (V=1.5-2 l) with water taken from the river and will be given permanent aeration until transportation to the aquaria.
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Fig. 3 Fertilized eggs in petridish
The eggs were placed in an aquarium (180 l) (Fig.4) with permanent aeration, 10-20 cm water level, 24- 26 O C, natural illumination. It was preferred to use the aquarium with the broad bottom to avert the intimate contact of eggs. The wide distribution of eggs prevented the rapid spread of fungi and other infections, and the initiation of premature massive hatching. The water at the aquarium has to be changed daily and dead eggs had to be removed. Most of the water may be changed at hatching to prevent premature massive hatching. Larvae began to feed at the 6-7 dpf (day post fertilization). We used Artemia salina nauplii and Tetra BabyMin (Tetra) to feed larvae during the first 2-3 weeks after hatching. When the feeding of larvae began, we started to clean the aquarium bottom daily and changed ¼ of water amount. The water level must be progressively increased. Larvae and juveniles were fed artificial food Biomar.
Fig.4 The eggs are incubated in aquaria (180 l)
It’s necessary to prevent the overcrowding of larvae and juveniles in aquaria. We put about 500-700 eggs per aquarium up to 9-10 dpf, time when larvae fill the swim bladder and begin to swim. Then we reduced twice the number of larvae and rear them up to the silver pigmentation of abdomen and reduced twice the number of larvae again. Further we progressively decreased the number of larvae per aquaria. Density should be 20-30 juveniles per aquaria at the time of squamation (90-100 dpf ).
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Fig.5 : One year-old L.megasoma
Fig. 6 : Two year-old L.megasoma
Fig. 7 : Four year-old L.megasoma
After squamation juveniles were transferred to the open air ponds (Fig.8). We used unfiltered and untreated water from the Lake Tana for rearing large barbs at the ponds. As the water chemistry was changing from time to time, it was very important to measure the oxygen and the acidity level of the ponds in order to prevent the spontaneous outbreak of unicellular algae. Fish in the pond should be fed artificial food. However, as artificial food requires additional feeding resource, the main food supply was crustacean and insect larvae suppliedt to the pond with lake water.
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Fig.8 : Concrete pond
Results Our results show that the large barbs reared at the described above conditions developed well and reached sexual maturity at the 2-3 years old age (Figs 5, 6 and 7). This will allow us to pursue further experiments to breed large barbs under artificial conditions and create an artificial large barbs stock in the Bahir-Dar Fishery andandOther Aquatic Life Research Center.
Discussion Discussions on the conservation of biodiversity usually focus on terrestrial habitats, especially on rain forest ecosystems (Myers 1979, Simberloff 1984, Wilson 1989). Because of this bias, the value of aquatic communities, which are less accessible for direct observations, is often not fully appreciated. Fishes on spawning migrations are especially vulnerable to overfishing (Craig 1992), because their exploitation can, in extreme cases, lead to a dramatic decrease in the number of recruits (Gabriel et al. 1989). In Lake Tana, at present, there is no limitation on the number of gill nets used, although the most commonly used mesh size (100 mm) ensures that the smallest fishes caught are sexually mature. The recent observation on the ecology of Lake Tana Labeobarbus species flock stressed that it is in danger of extinction due to habitat deterioration including the presence of recruitment overfishing at the time of spawning migration. The present study provided a method by which Lake Tana Labeobarbus could be artificially induced to spawn so that a large-scale propagation and stocking program could be initiated in selected areas.
Conclusion We believe that the artificial large barbs restock should save the unique endemic species of Lake Tana large barbs, restore the large barbs population in the lake and preserve the fish resource for people living around the lake.
Acknowledgments The study was done within the framework of the Joint Ethio-Russian Biological Expedition (JERBE) and carried out with financial support from The Russian Foundation for Basic Research (project nos. 03- 04- 48329 and 06-04-48352). We thank Dr. Eshete Dejen, Dr. Andrei Darkov, Mrs. Sewmehon Demissie, and Mr. Alayu Yalew.
References Banister, K.E (1973) A revision of the large Barbus (Pisces: Cyprinidae) of East and Central Africa: - Studies on African Cyprinidae, part 2. Bulletin of the British Museum of Natural History (Zoology) 26: 167-180. Kofield, I and K., Carpenter (1984) Cyprinid of Lake Lanao, Philippines: taxonomic validity evolutionary rates and speciation scenario’s In: A.A, Echelle and I. Kornfield (Eds); Evolution of Species flocks: 69- 83, University of Maine at Orono press, Orono, Maine. 137 Ma nagement of shallow water bodies ..., EFASA 2010
Nagelkerke, L.A.J. and Sibbing, F.A. (2000) The large barbs ( Barbus spp., Cyprinidae, Teleostei) of Lake Tana (Ethiopia), with a description of a new species, Barbus osseensis . Neth. J. Zool. , 50,179-214. L. A. J. Nagelkerke, F. A. Sibbing, J. G. M. van den Boogaart, (1994). “The Barbs ( Barbus spp.) of Lake Tana: A Forgotten Species Flock.,” Environ. Biol. Fish . 39 , 1–21. Craig, J.F. (1992). Human-induced changes in the composition of fish communities in the African Great Lakes. Reviews in Fish Biology and Fisheries 2: 93-124. Gabriel, W.L, Sissenwine, M.P, Overholtz, W.J. (1989). Analysis of spawning stock biomass per recruit: an example for Georges Bank haddock. North American Journal of Fisheries Management 9: 383-391. Myers N. (1979). The sinking ark: a new look at the problem of disappearing species . Oxford (UK): Pergamon Press. Simberloff, D.S. (1984). Mass extinction and the destruction of moist tropical forests. Zhurnal Obshchei Biologii 45: 767-778. Wilson, E.O. (1989). Threats to biodiversity. Scientific American 261: 108-117.
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Growth, mortality and recruitment of Clarias gariepinus in the northern part of Lake Tana
Belay Abdissa, Bahir Dar Fisheries and Other Aquatic Life Research Center P.o.Box 794 E-mail- [email protected], Bahir Dar, Ethiopia
ABSTRACT : Growth, mortality and recruitment patterns of the African catfish, Clarias gariepinus were determined based on length frequency data from 2002 research sampling programs in the northern part of Lake Tana. Values of L ∞ = 81.9 for female and 87.15 cm (TL) for male and K = 0.52 and 0.45 yr -1 for female and male, respectively, were computed. The total mortality (Z) estimates from each curve analysis for female and male were Z = 1.19 and 1.12 yr -1, with a natural M of about 0.79 and 0.74 yr -1 .respectively. The single highest peak for recruitment was in July, indicating recruitment of one cohort per year. These results are discussed and compared to other African lakes.
Key words/phrases : Clarias gariepinus, growth, Lake Tana, mortality, recruitment
Introduction The northern part of Lake Tana covers 75% of the entire lake. Very little research activity has been done so far as compared to the narrow Bahir Dar Gulf which was relatively well- studied. Lake Tana is the largest fresh water body in Ethiopia (3,150 km 2) and the source of Blue Nile River. An endemic flock of 15 large Barbus spp. (Cyprinidae), Oreochromis niloticus (Cichlidae), Clarias gariepinus (Claridae) and Varicorhinus beso (Cyprinidae) are commercially important fish species in the lake. In addition, three ‘small barb” species (< 100 mm- fork length), B.humilus , B.pleurogramma and B.tanapelagius and some species of the genus Garra (Cyprinidae) have been reported in this lake. Serious decline of the stocks of endemic ‘large barbs’ and moderately susceptible C. gariepinus to future fishing pressure in Lake Tana (de Graf et al ., 2000b) raises the question of management option. Demographic assessment is a basic requirement for rational fisheries management. Such assessments can be made only if the individual growth, mortality and recruitment patterns of fish populations are known. Therefore, information on the demographic status of the fish will be needed. In an ideal world, tagging and utilization of standard technique for ageing are based on the identification of mark on their scales; otoliths or other hard structure and such yechniques make excellent method for demographic analysis. Unfortunately, this method could not be used here; instead length-frequency analysis methods are employed. The aim of this study was to estimate the growth parameters, mortality rates and recruitment pattern of Clarias gariepinus from the northern part of lake Tana.
Materials and methods Study area: Lake Tana is the largest lake in Ethiopia with a surface area of 3150 km 2, a maximum length and width of 78 andand 68 km, respectively, and a maximum depth of 14m and mean depth of 8.9m. The shallow littoral zone (depth 0 – 4m) is relatively small, ca. 10% (315 km 2) of the total surface area of the lake. The sub-littoral intermediate zone contains no macrophytes and occupies ca.20% (630 km 2 ) of the lake area (depth4- 8 m), whereas the pelagic deep offshore zone is 70% (2205 km 2) of the lake surface area and is relatively deep (depth 8- 14 m). Sampling sites and collection Length – frequency data for Clarias gariepinus was obtained through feeding andand reproductive behavior of the African catfish research program conducted on a monthly basis at 4 sampling sites. Samples were collected from January to December 2002 in the northern part of Lake Tana at four different habitats (Fig.1) whicht consisted of A) River mouth with papyrus and submerged vegetation B) shallow littoral zone (average depth 2m) with muddy bottom bordered by papyrus bed, and C) an open water zone, ca 10m deep with sandy/ muddy bottom. Sampling was carried out using gill nets with stretched mesh sizes of 60, 80, 100, 120 andand 140 mm each with 50 meter length and 3 m depth. Each station was sampled once in each month. The nets were set overnight between 1700h and 1800h and were lifted between 0600 hours and 0730 hours the next
139 Ma nagement of shallow water bodies ..., EFASA 2010 morning. Data collected for each individual fish included total length (cm), wet (ungutted) weight (g), gut content, and sex and gonad (maturity) stage. Data analysis : The monthly length- frequency data were grouped into 5 cm length classes (midpoints at 23 cm, 25 cm, etc). Since sex and maturity were determined, the results refer to both sexes separately and in combination. Growth parameters, mortality and recruitment were estimated using the FiSAT (FAO- ICLARM Stock Assessment Tools) computer package (Gayanilo et al., 1996). Estimation of growth parameters : In the tropics, accurate length at age data are difficult to obtain as there may not be strong fluctuations in environmental conditions throughout the year (Sparre, andet al., 1989). Therefore, length frequency distribution (LFD) data were used to estimate age and growth. The ELEFAN I program incorporated in the FiSAT software was used for estimating the growth parameters of the von Bertalanfy growth equation:
Lt = L ∞∞∞ (1 – e –k(t – to) (1) Where L t is length at age t, L ∞ is the asymptotic length, k is a growth constant and t o is the “age” the fish would have been at zero length (Gayalino et al . 2002). The growth performance index Φ’ using the formula of Pauly and Munro (1984).Phi prime ( Φ’) was used to evaluate the reliability of L and K estimates (Sparre, Ursin and Venema 1989
ΦΦΦ’ = log k + 2 log L ∞∞∞ (2) and the potential longevity t max calculated using Pauly (1983). tmax = 3/k (3) Estimation of mortality rates : Total mortality (Z) was estimated from a length – converted catch curve analysis as described by Pauly (1984):
Ln(N i/∆∆∆ti) = a + b i (4) Where Ni is the number of fish in length class i, t i is the time needed for the fish to grow through length class i, ti is the age (or the relative age, computed with t o = 0) corresponding to the midlength of class i, and where b, with sign changed, is an estimate of Z. Natural mortality rate ( M) is usually a difficult parameter to estimate in the absence of an unexploited resource (FAO 1993). Most of the procedures rank no higher than 'qualified' guesses (Sparre et al . 1989). In the present study the empirical formula of Pauly (1980) was used:
Ln (M) = -0.0066 - 0.279 ln (L ∞∞∞) + 0.6543 ln (K) + 0.4634 ln (T) (5) Where T is the mean environmental temperature °C. Once Z and M were obtained, then fishing mortality (F) was derived from the relationship. F = Z – M (6) and the exploitation rate (E) was obtained by the relationship: E = F/Z = F/ (F + M) (7) Also in ELEFAN routine recruitment pattern are displayed graphically which indicate the peak
spawning season. Using growth parameters L∞, k and t o available as input parameters and based on either original length- frequency data or restructured data (Moreau and Cuende, 1991). Preliminary
estimation of L ∞ and of the ratio Z/K was obtained using ELEFAN routine according to Wetherall (1986) as modified by Pauly (1986).
Results Growth parameters : Size distribution of C. gariepinus ranged from 207 to 850 mm TL, and mean length in each month is shown in Fig. 2.Preliminary estimates of L ∞ using Wetherall (1986) gave the value of = 81.47 cm and 84.66 cm for female and male, respectively (Fig.3) (Fig.4). The growth -1 parameter estimates of L ∞ and K values were 81.90 cm and 0.52 yr for female, and 87.15 cm and 0.45 yr -1 for male. The growth performance index ( Φ’) values were 3.54 and 3.53 for female and male, respectively. The longevity for female and male were t max ≈ 6 and 7year, respectively. Mortality : The average water temperature in Lake Tana is 23 °C (Tesfaye, 1998). Therefore, the natural mortality coefficient, M, which was assumed to be constant throughout the study period, was estimated to be 0.79 and 0.74yr 1 for female and male, leading to fishing mortality values of 0.40 and 0.38 with
140 Ma nagement of shallow water bodies ..., EFASA 2010 the same 0.34 exploitation rate for female and male sexes, respectively (Fig.4).The length- converted catch curve analysis produced total mortality estimates for female and male as Z = 1.19 and 1.12 yr -1 (Fig.5) for the range of ages 2 to 7. Recruitment: The annual recruitment pattern (Fig.6) for C.gariepinus in the northern part of Lake Tana suggest a major breeding period from April to August with prominent peak during the month of July. Thus suggests a single cohort per year.
Fig. 1. (a) Location of Ethiopia in the Horn of Africa, ( b) Lake Tana and itsmain in- and out- flowing rivers and the Blue Nile.
Fig.2. Length frequency distribution of C.gariepinus from Lake Tana.
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Female Male
Fig.3: Preliminary estimates of L ∞ and Z/K obtained from length – frequency data using the Wetherall’s method (1986)
Fig.4 : Evaluation of the growth of Clarias gariepinus in northern Lake Tana, using ELEFAN I on -1 length- frequency data (L ∞ = 81.90 and 87.15 cm where as k = 0.52 and 0.45 yr for females (upper panel) and males (lower panel)
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Fig.5: Length converted catch curve analysis using ELEFAN II on length – frequency data
Fig. 6 : Recruitment pattern of C.gariepinus in northern Lake Tana as obtained using ELEFAN II length- frequency data .
Discussion Growth of fish may be estimated using annuli on hard parts like otoliths, mark recapture experiments or by analyzing length – frequency data (Sparre and Venema, 1998). Here we used length- frequency analysis because of absence of logistic to process the hard parts of the specimens and we were unable to examine daily rings. Various growth parameter prediction models were used to estimate L and Kohn (1986) suggested that if parameter values were estimated by formal optimization methods, it was essential to show that these estimates were reasonable and reliable for the biological data that the model was depicting. Therefore, in line with this view, the estimates of VBGF parameters, L should be reasonably close to the maximum fish length observed in the samples (Taylor 1958; Pauly 1979; Moreau 1987), t0 should be smaller than 0 so that the fish at age 0 could have a positive length (Moreau 1987), and K might vary between 0 and 1 per year for fish species with long life spans (Pauly 1978); the relevant estimates for C. gariepinus in northern Lake Tana conform to all these criteria. 143 Ma nagement of shallow water bodies ..., EFASA 2010
The estimates of growth parameters are in the range of already available values from the literature and are comparable with that reported for C. gariepinus in various African water bodies (Table.1). Lake Sibaya of South Africa and Lake Malawi reported similar value of L = 67.20 and value of K= 0.52 and 0.22 for female C.gariepinus . The male C.gariepinus value of L and K were 76, and 0.35 and 113 and 0.11 for Lake Sibaya and L.Malawi, respectively. The Bahir Dar gulf of L.Tana value of L and K was 85 and 0.20 for female and 90 and 0.2 for male. For the Lake Le Roux of South Africa L and K value was 102 and 0.45 for female and 115 and 0.31 for male C.gariepinus, respectively. The value obtained
from the current study L∞ = 81.90 and 87.15 cm for female andand male C.gariepinus whereas k = 0.52 and 0.45 yr -1 for female and male, respectively. These results were similar with the above results obtained from different African lakes, rivers and dams. The Phi prime (Ø') value of C.gariepinus was used to evaluate the reliability of L and K estimates. Moreau et al.,and (1986) indicated that species within the same family are expected to have similar Ø' values, as Ø' values are normally distributed. From various African water bodies the Ø' value of C.gariepinus was found to range from 3.00 to 3.67 (http://www.fishbase.org/). In Lake Malawi, C.gariepinus has a Ø' value of 3.00 for female and 3.13 for male. On the other hand, L.Le Roux of South Africa shows relatively higher Ø'- value of 3.67 and 3.61 for female and male catfish, respectively. Compared with the Bahir Dar Gulf Ø'- value of female was 3.16 and 3.21 for male. The current study of northern Lake Tana have higher Ø’- value of 3.54 and 3.53 for female and male, respectively (Table1). TMortality rate was similar for the female and male C.gariepinus in Lake Tana.
Table 1 : Parameter estimates (asymptotic length ( L∞), growth constant ( K) and growth index ( Φ) of C.gariepinus in African Lakes, Rivers and Dam.
L∞ Length K Sex T° C Φ' Country Locality (cm) Type (1/y) 67.20 TL 0.517 F 3.37 S. Africa Lake Sibaya 67.20 TL 0.220 F 22.50 3.00 Malawi Lake Malawi 76.00 TL 0.349 M 3.30 S. Africa Lake Sibaya 79.00 TL 0.170 F 26.50 3.03 Malawi Shire River 85.00 TL 0.200 F 22.00 3.16 Ethiopia Bahir Dar Gulf, Lake Tana 88.00 TL 0.230 F 21.50 3.25 S. Africa Hartbeespoort Dam 90.00 TL 0.200 M 22.00 3.21 Ethiopia Bahir Dar Gulf, Lake Tana 102.00 TL 0.450 F 17.50 3.67 S. Africa L.Le Roux 109.00 TL 0.210 M 21.50 3.40 S. Africa Hartbeespoort Dam 113.00 TL 0.105 M 22.50 3.13 Malawi L. Malawi 115.00 TL 0.310 M 17.50 3.61 S. Africa L. Le Roux 128.00 TL 0.190 M 21.50 3.49 Zimbabwe Lake McIlwaine 137.00 TL 0.171 M 3.51 S. Africa Boskop Dam AS 139.00 TL 0.090 M 26.50 3.24 Malawi Shire River 156.00 TL 0.084 M 3.31 S. Africa Incomati-Limpopo AS 195.00 TL 0.090 F 3.53 S. Africa Boskop Dam AS
The period of the main recruitment pulse lasts from April to August. This is also supportedby Abebe et al (2006) who suggested that the main spawning season of Clarias gariepinus in Lake Tana extends from April to July. Belay andand Teferi, (2006) suggested that Clarias gariepinus spawns at the onset of the rainy season. This is in agreement with the present study.
Conclusion The results suggest that C.gariepinus males grow bigger in length than females in Lake Tana. The female fish were more susceptible to fishing mortality than males which leads to decline of the catfish 144 Ma nagement of shallow water bodies ..., EFASA 2010 population since females are the ones which play a significant role in perpetuation of generations.The Catfish fishery exploitation rate in the northern part of Lake Tana accounts for about 34% which was moderate. The major breeding period was found from April to August with prominent peak during the month of July. However the demographic status were normal at this time; further investigation are needed to monitor lake-wise demographic status of C.gariepinus and its possible over – fishing , as has already been observed in some parts of Lake Tana.
Acknowledgments I would like to thank all the ex- Gorgora Fishery Research Sub- Center staff for their help, and my thanks goes to the late Abba Amare of the Bergida Mariam Monastry Abbot and the monk community for their help in arranging resting place during our work.
References de Graaf, M., Dejen, E., Sibbing, F. A. and Osse, J. W. M. (2000b). The piscivorous barbs of Lake Tana (Ethiopia): Major questions on their evolution and exploitation. Neth. J. Zool. 50 , 215–223. Gayanilo, F., Sparre, P. and Pauly, D. (2002). FiSAT II User’s Guide. Food and Agriculture Organisation of the United Nations . Gayanilo, F.C. Jr. , P/ Sparee and D. Pauly, 1996. The FAO-ICLARM Stock Assessment Tools (FiSAT) User's Guide. FAO Computerized Information Series (Fisheries) . No. 8. Rome, FAO, 126 p. KohnM.C. (1986) Strategies for computer modelling. Bulletin of Mathematical Biology 42 , 417–426. Moreau, J., (1988). Estimation of natural mortality from selection, and catch length-frequency data: a modification of Munro's method and application example. ICLARM Fishbyte , 6(2): 10-12. Moreau, J. and F.X. Cuende, (1991). On improving the resolution of the recruitment patterns of fishes. ICLARM Fishbyte , 9(1): 45-46. Pauly, D., (1979). Gill size and temperature as governing factors in fish growth: a generalization of von Bertalanffy's growth formula. Berichte des Instituts für Meereskunde an der Univ. Kiel. No. 63, xv + 156 p. Pauly, D., (1980). On the interrelationships between natural mortality, growth parameters and mean environmental temperature in 175 fish stocks. J. Cons. CIEM , 39(3):175-192. Pauly, D., (1986). On improving operation and use of the ELEFAN programs. Part II. Improving the estimation of
L∞. ICLARM Fishbyte , 4(1):18-20. Sparre, P. and S.C. Venema, (1993). Introduction to tropical fish stock assessment. Part 1-Manual. FAO Fish. Tech. Pap . (306.1) Rev. 1: 376 p. Sparre, P. and Venema, S. (1998). Introduction to tropical fish stock assessment. Part 1 . Manual. FAO Fisheries Technical Paper. No. 306.1, Rev. 2 . Rome: FAO. Tesfaye Wudneh (1998a) Temporal and spatial patterns in the gillnet fishery for Clarias gariepinus , Oreochromis niloticus and Barbus spp. and the formulation of the catch effort data recording system. pp. 85-102. In: Biology and management of fish stocks in Bahir Dar Gulf, Lake Tana, Ethiopia. PhD thesis, Wageningen Agricultural University, Wageningen, The Netherlands Wetherall, J.A., (1986). A new method for estimating growth and mortality parameters from length frequency data. ICLARM Fishbyte , 4(1): 12-14.
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Status of Lake Tana commercial fishery, Ethiopia
Dereje Tewabe and Goraw Goshu Amhara, Regional Agricultural Research Institute (ARARI) P. O. Box 794, Bahir Dar, Ethiopia, [email protected]
ABSTRACT : The status of Lake Tana Fishery was evaluated from analysis of commercial catch data of number I fishers cooperative. The data collection was carried out from September 2003 to September 2009. Results indicated that Nile tilapia (Oreochromis niloticus), African catfish (Clarias gariepinus) and species flock of endemic, large Labeobarbus spp. were the three main species groups targeted by commercial gillnet fishery of Lake Tana and form 65 %, 20 % and 15 % of the annual catch compositions of fish species during the study period, respectively. There was significant variability among sampling years encompassing temporal aspects. Especially, commercial catch of O. niloticus was significantly booming up to 2007 and declined afterwards. The most likely explanations for the declining catch of O. niloticus and others are the illegal use of undersized monofilament gillnet imported from Sudan town (Gelabat) and the harmful increase of the commercial gillnet fishery targeting the spawning aggregations of L. barbus spp. and C. gariepinus in the river mouths and littoral areas. The observed decline in the commercial catch of O. niloticus and others stress the need for the urgent development of a management plan focusing on controlling import of undersized monofilament gillnet, fishing effort and gear restrictions in the river mouths and major tributaries during the breeding seasons and implementing the regional fishery legislation .
Key words/phrases : Commercial fishery, monofilament, spawning grounds, spawning seasons, sustainable management.
Introduction Ethiopia is endowed with significant area of inland water, including about 7,400 km 2 of lakes and reservoirs, and about 7,000 km of rivers. Estimates of maximum sustainable yields might allow a production growth between 30,000 to 40,000 tones per year, from the main lakes only. The rivers fishery potential is roughly estimated at about 5000t/yr. however, the estimated annual production in 1992/93 increased by about 30 % leading to an estimated fish harvest of 6,500 tones (FAO, 2003). Tthe incidence, depth and severity of food poverty are very serious in Ethiopia. The national food security strategy has therefore, been formulated with an overall objective to raise the level of food self reliance nationally and ensure household food security strategy of the regions, much more comprehensive packages of interventions are needed to ensure food security in the regions. It can be stressed that the fisheries and aquaculture sub-sector of the livestock sector can play a significant role for the regions’ food security as far as resources of fishery is numerous. Lake Tana, the source of the Blue Nile, is Ethiopia’s largest lake; it probably was formed during late Pliocene or early Pleistocene times. It now covers an area of about 3150 km 2 and has an average depth of 8 m, with a maximum of 14 m. It is situated at an altitude of 1830 m and can be characterized as oligo-mesotrophic Lake (Rzoska 1975; 1976; Demeke Admasu, 1986) with a very truncated fish fauna (Green wood, 1976) that is it is poor in species and families. There is only one representative of the family Cichlidae: Oreochromis niloticus, a very wide spread species in Africa. The three species of Clarias (Family Claridae), that Boulinger ( 1911) described for the lake (Including the endemic Clarias tsanensis Boulinger 1902), have recently been synonyms to C larias gariepinus , the most common member of this genus (Teugels, 1982). The largest family in the lake is the Cyprinidae, which is represented by three genera: Varicorhionius, with one single species V. beso Garra, for which Boulenger (1911) described two species in Lake Tana: G. quadrimaculata and G.dembensis and the last well described genus of Cyprinidae fishes from Lake Tana Barbus, which has been revised several times as a result of which seventeen morphotypes of lake Tana Labeobarbus were identified. According to Martin deGraaf (2003), to prevent extinction of the unique Barbus species flock, effort to control restrictions near the river mouths during August- September (peak breeding period) have to be implemented immediately to protect the vulnerable spawning aggregations. Since its introduction in 1986, little has been documented about the development and characterstics of the commercial gillnet fisheries and development of the three targeted 146 Ma nagement of shallow water bodies ..., EFASA 2010 species groups, L. Barbus , C. gariepinus , and O. niloticus . This lack of knowledge about the natural resources and the impact of the commercial gillnet fishery is one of the main reasons why to date no management plan or fisheries regulations exist in L. Tana. However, in recent years fishers have noted a drastic reduction of their catches in L. Tana. This stresses the need for sound data on Lake Tana’s fish and fisheries in order to provide a scientific base for advice on development of a management plan and fisheries regulations. Therefore the purpose of the study was to understand the general trend of catch compositions and weight of Lake Tana commercial fishery and evaluate status of fishing activities in Lake Tana.
Objectives of the study General objective: The major objective of the study was to generate baseline scientific information/ data about economically important and commonly found fish species for management and sustainable utilization of the resources, and recommend ways and means of conserving the diversity and stock of the icthyofauna of L. Tana. Specific objectives: • To identify fish composition of annual catch, • To evaluate the weight of annual catch, and • To examine the fishing activity at the landing and fishing sites.
Materials and methods Study site was at the landing site of Bahir-Dar number one fishers cooperative station. Data were collected by identifying fish species just after arrival of motorized boat at the station and taking their weight on daily basis using a sensitive balance. Data collection was carried out from September 2003 to September 2009. Reconnaissance survey was conducted to overview the fishing site and fishing materials at different landing and fishing sites. Survey was conducted by collecting information from the beneficiaries and fishers from motorized and reed boat by interviews while they were fishing. Fishing gears type and size were assessed at ther landing and fishing sites. Data was analyzed using statistical software (SPSS version 16) and descriptive statistics .
Results and discussion Total catch composition and weight: The three main species groups targeted by commercial gillnet fishery of L. Tana during the study were found to be a species flock of endemic, large Labeobarbus spp., African catfish ( Clarias gariepinus ) and Nile tilapia ( Oreochromis niloticus ) (Fig. 1). Total catch from Lake Tana by Bahir- Dar fishers number one cooperative recorded during the study was O. niloticus 1689.1 ton, C. gariepinus 527.3 ton and L. barbus 383.8 ton. Annual catch shows that, compositions of fish species for seven consecutive years were mainly O. niloticus which constituted 64.96 %, C. gariepinus 20.28 % and L. barbus 14.76 % of the total catch (Fig. 2). Species diversity for L. barbus species was more diverse, which enables Abay basin to be rich in fish diversity due to L. barbus endemicity exclusively in L. Tana. The previous two species were more abundant in total catch , but L. barbus species was rare, the most possible explanation is due to inappropriate fishing burden for several years on their spawning grounds and absence of applicable fishery legislation in the region that make L. barbus composition rare in commercial catch composition of fishers of Bahir-Dar number one fishers cooperative. Full time fishers and part-time fishers of Lake Tana vicinity target L. barbus species at spawning grounds especially at all Lake Tana tributary river mouths and upstream rivers while fishes migrate for breeding purpose.
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Fig. 1 : Total catch of commercial gillnet fishery of L. Tana by Bahir-Dar number one fishers cooperative from 2003 to 2009
20.28%
O. niloticus L. barbus C. gariepinus 14.76%
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Fig. 2 : Total catch percentage of commercial gillnet fishery by Bahir-Dar number one fishers cooperative from 2003 to 2009
Fishing Activities : Lake Tana fisheries consist of mainly artisanal; predominantly subsistence fishery, conducted from papyrus reed boats ( tankwa ), and resembled those of ancient Egypt. The fishermen, who use mainly fish traps and small gill nets, are almost exclusively members of the reed boat fishers association formed in 1986 as a motorized commercial gillnet fishery by Amhara fishermen in cooperation with fishermen in Urk (Netherlands). As a result currently fishing with motorized boat has become common; fore example Bahir-Dar number one fishers’ cooperative has more than 70 motorized boats. Commercial catches of large barbs in Lake Tana over the last decade have sharply decreased, due to over fishing in river mouths during fish migration to their spawning rivers (de Graaf et al ., 2004). However, at the 4 th Pan African Fisheries and Fish Association (PAFFA) conference held in September 2008 at Addis Ababa, it was indicated that habitat degradation at the breeding ground of fish (rivers, tributaries and wetlands) contributed more than overfishing for the sharp decline. The present study found that almost all fishers (both reed boat and motorized boat) fishing pressure is mainly concentrated during the breeding season and on the spawning ground of each species. O. niloticus fishing is carried out inthe littoral regions, C. gariepinus in flooded areas, littoral and river mouths. L. barbus is mostly targeted at river mouths and a little distance towards upstream (Fig. 3). The most shocking fishing 148 Ma nagement of shallow water bodies ..., EFASA 2010 activitythat leads to overall collapse of L. Tana fishery resource is using undersized monofilament gillnet imported from Sudan town (Gelabat) market starting from 2008 (personal communication with fishers). It has become common practice to set 5 cm up to 7 cm stretched mesh by all fishers during the peak spawning season ( pre-rainy season), peak rainy season and post rainy season in all spawning grounds (Fig. 4).
Fig. 3 : Catch of commercial gillnet fishery from Enfranz River mouth tributary of LakeTana during L. barbus spawning season .
Fig. 4 Monofilament gillnet introduced to L. Tana commercial gillnet fishery from Sudanese market (Gelabat)
Fishing by monofilament gillnet is performed mostly from early in the morning up to 10 a.m by disturbing spawning ground with strong stick to kick surface water for several times and several places until they caught enough catch. The demand of filleted fish by immediate fish traders who export L. Tana fish mainly to Addis Ababa and Sudan as well as different towns of the country trigger fishers to have catch from small sized fish population by using illegal small sized monofilament gillnets which have never been practiced during previous years. The other fishing practice recently started by many of fishers is using small mesh sized cast net (usually < 4 cm) at the shore sides of L. Tana especially during O. niloticus spawning seasons (Fig. 5).
Fig. 5 : Fishing with 4-5 cm stretched mesh size cast net on shore of L. Tana
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During both the day time and night, monofilament gillnet is hidden somewhere in the vicinity of L. Tana covered by vegetation at littoral areas. This makes it easier for the fishermen to set the appropriate gillnet for the whole night and they set off early in the morning and left their gillnet for the next day harvesting (Fig. 6).
Fig. 6 : Monofilament gillnet during off time (day time) hidden in littoral region.
The commercial gillnet fisheries was monitored during 2003 to 2009. According to experimental trawling program of de Graaf et al ., (2006) the commercial catch of large specimens of African catfish (>50 cm) and Nile tilapia (>20 cm) decreased significantly over the last 10 years time, but recruitment of young fish to the adult populations was not negatively affected. During the same period the commercial catch of riverine spawning Labeobarbus spp. declined by 75 %. In the experimental fishery a similar decrease was observed and the populations of juvenile L. barbus in the littoral (Length range: 5-18 cm) decreased even by more than 85 % (de Graaf et al ., 2006). The major reason for the collapse of these fish species is due to destructive fishing during their spawning season and destruction of the river ecology that serves as a spawning ground. These species form aggregations in the river mouths in August-September, during which time they are targeted by the commercial gillnet fishery. Annual catch distribution pattern : The present study showed that O. niloticus show an increasing order starting from 2003 up to 2007, but after 2007 it sharply declined year after year for consecutive two years. C. gariepinus and L. barbus did not show significant change year after year except L. barbus species which showed significant decline during 2007 (P < 0.05). From annual catch composition O. niloticus played a leading catch by weight this is because of targeting the spawning seasons and spawning aggregation grounds. The other two species had been targeted illegally for several years at both spawning seasons and grounds; there is no remarkable catch whenever fishing effort is applied. Overfishing of L. barbus near and in river mouths and upstream in the rivers on and near the spawning grounds by fishers for several years has reduced their abundance to a very low level.
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At every year of commercial gillnet catch of O. niloticus took a leading dominant species by weight starting from 2003 to 2007 at an increasing order. The total amount commercial catch of O. niloticus during 2007 is 450 tons, but after a year of 2007 it started to become decline. The total annual commercial catch declined during 2008 and 2009 at decreasing order, respectively (Fig. 8). Catch weight increment of O. niloticus from 2003 up to 2007 was due to fishing pressure at spawning grounds with illegal monofilament introduction, this is supported by the amount of catch recorded at a particular seasons, which are peak spawning seasons of O. niloticus (Feburary, March and April). The highest catch of O. niloticus was recorded during 2007 which was 452.7 tons/year and least was recorded during 2003 with 101.1 tons/year and the mean catch by weight is 241.3 tone/year. The highest catch of C. gariepinus was recorded during 2007 which was 101.6 tons/year and least was recorded during 2005, which was 57.5 tons/year and the mean catch by weight was 75.3 tone/year. The highest catch of L. barbus was recorded during 2008 which was 92.4 tons/year and least was recorded during 2007, which was 0.7 tons/year and the mean catch by weight was 54.8 tons/year (Fig. 7).
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Fig. 9. Total catch distribution on monthly basis from 2003 to 2009 from catches of Bahir-Dar number one fishers cooperative
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Total catch distribution shows that March hadt the highest catch and February and April followed next. May, Jun, July and August exhibit the second category for better catch distribution. The least was recorded from September up to December (Fig. 9). Especifically L. barbus annual catch started to increase during July, peaked in August and started to decline in September. September is the peak spawning season for L. barbus species. The highest catch was recorded for C. gariepinus in June lowed by July, which is the spawning season for C. gariepinus . The other seasons exhibit least production. The highest total catch for O. niloticus was recorded during March followed by February and April, respectively (Fig. 10).
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Fig. 10. Total catch distribution of three species on monthly basis
Fisher’s trip of fishing days per year increased from 2003 to 2005. This showed that fishers used an appropriate fishing material throughout the year. But during year 2006 fishing trips declined and it remaineds constant until 2008. Trips per year during 2009 again started to decline. This indicated that fishing was carried out during the selected seasons, which is the breeding season and at the same time breeding ground of the most economically important fish species of Lake Tana (Fig. 11).
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Fig. 12 . CpUE using kg/trip
CpUE using kg of the catch per trip showed that during 2005, it declined and from 2005 onwards up to 2007 it increased and again after 2007 it declined (Fig. 12). The number of fishers from 2003 up to 2005 was almost the same, but starting from 2005 up to 2009 it was on an increasing order (Fig. 13); this implied that the number and length of fishing gears increased with time.
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Fig. 13 : Number of fishers per year.
Conclusion and recommendation The commercial gillnet catch of O. niloticus showed changes in the leading dominant fish species each year starting from 2003 to 2007. The total amount of commercial catch of O. niloticus during 2007 was 450 ton, but after 2007, it started to decline. Total annual commercial catch declined during 2008 and 2009. Catch weight increment of O. niloticus from 2003 up to 2007 was due to fishing pressure on the spawning grounds with illegal monofilament introduction. This is supported by the amount of catch
153 Ma nagement of shallow water bodies ..., EFASA 2010 recorded at particular seasons, which are peak spawning seasons of O. niloticus (Feburary, March and April). By way of recommendation, the following should be enacted: • Closed seasons and spawning grounds for different fish species have to be implemented. • Prohibit illegal fishing such as using small stretched mesh size gillnet, monofilament gillnet, beach seines during spawning aggregations, small mesh sized cast net at lake shore, which are the major sites for breeding and nursery. • Generally implementing the existing fishery legislation is a vital issue to alleviate the problems that Lake Tana fishery resource has encountered.
References Boulenger, G.A. (1905). The distribution of African freshwater fishes. Nature 72(1869 ):413-421. Boulenger, G.A. (1911). Fresh water Fishes of Africa . Vol. II, pp.1-512. London: British Museum (Natural History). Degraaf, M. (2003). Lake Tana‘s Piscivorous Barbs (Cyprinid, Ethiopia) PhD thesis.Wageningen University. The Netherlands. DeGraff, M. , Marcel, AM, Machiels, M., Tesfaye Wudneh and Sibbing, FA. (2004). Declining stocks of Lake Tana’s endemic Barbus species flock (Pisces: Cyprinidae): natural variation or human impact ? Biol. Cons. 116: 277-287. DeGraaf M, van Zwieten, P.A.M., Machiels M.A.M., Lemma, E., Wudneh T., Dejen, E. and Sibbing F.A. (2006). Vulnerability to a small-scale commercial fishery of Lake Tana’s (Ethiopia) endemic Labobarbus compared with African catfish and Nile tilapia: An example of recruitment-overfishing? Fisheries Research 82: 304- 318. Demeke Admasu (1986). Report on Limnological Studies on Lake Tana, pp.1-44. Addis Ababa, Ethiopia: Addis Ababa University, Dept. of Biology, internal report. FAO, FID/CP/ETH/, (2003). Fishery Country Profile. Rev.3. pp. 1-6. Green, Wood, P.H. (1976). Fish Fauna of the Nile . In : The Nile, Biology of an ancient River (J.Rzoska, Ed.), pp. 127-141. The Hague, The Netherlands: Dr. W. Junk Publishers. Teugels, G.G. (1986). A systematic revision of the African species of the genus Clarias (Pisces;Clariidae). Annales de la Mussee Royal de l’ Afrique Central, Science Zoologique 247: 1-199.
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The biodiversity of fish communities of nine Ethiopian lakes along a north- south gradient: threats and possible solutions
Eshete Dejen 1, Jacobus Vijverberg 2 and Abebe Getahun 3 Food and Agricultural Organization of the United Nations, FAO Sub Regional Office for Eastern Africa Ethio-China Road P.O.Box 5536, Tel. 0918767549 email. [email protected] . Addis Ababa, Ethiopia 1 Netherlands Institute of Ecology (NIOO-KNAW), Centre for Limnology, Rijksstraatweg 6, 3631 AC Nieuwersluis, The Netherlands 2 Department of Biology, Addis Ababa University, PO Box 1176, Addis Ababa, Ethiopia 3
ABSTRACT : The fish populations of nine Ethiopian freshwater lakes, located along a north-south gradient, were sampled. Fish were collected in a standardized and quantitative way using multi mesh gill nets. Biodiversity in the two northern highland lakes is low, but not lower than predicted. L. Tana has a high biodiversity which is close to what is predicted, but four rift valley lakes have low biodiversity, much lower than predicted. Although the fish fauna of the two most southern rift valley lakes have a higher species diversity than the other investigated rift valley lakes, their diversity s also lower than predicted. We conclude that the studied fish communities, with the exceptions of those of L. Tana and the two most northern highland lakes, have a reduced biodiversity. Threats like overfishing, high sediment load and degradation of breeding habitats were identified. It is recommended that Ethiopia should clearly develop guidelines and directives for the gazetted fishery legislation and implement it through an enforcement agency. Moreover, catchments management (tree planting, soil conservation and controlled grazing) should be practiced to save the water bodies and their biodiversity. Key words /phrases: Community structure , conservation biology, fish assemblages, habitat degradation, size distribution, species abundance.
Introduction Conservation of biodiversity implies knowledge of the number and distribution of species of any particular area. As habitat degradation continues on a global scale, maintenance of species richness has become a central issue of conservation biology. This is particularly the case with the fish fauna of inland waters. Habitat alteration and destruction are generally the major causes of most extinction of freshwater fishes (Thomas 1994). Fish communities differ per water body, hence site-specific management is important in fishery biology and fish biodiversity conservation. In the past fishery biologists, particularly those working in tropical countries, traditionally have tended to consider fish in isolation, as a natural renewable resource, rather than as integral components of the aquatic ecosystem interacting with other components of the system. This attitude has led to various ecological disasters, therefore, a better understanding of the role of fish diversity in the functioning of ecosystems should be a precondition before manipulation of African inland waters is undertaken (Lévêque 1995). In Ethiopia the rate of degradation of the environment, mainly by deforestation and overgrazing of grasslands by cattle, is very high (Zinabu Gebre-Mariam 2002) and leads to approximately 1.5 billion tons of soil lost every year from the highlands (Tefera 1994). This has already resulted in a decrease in biodiversity of the fish fauna in the different drainage basins and the Rift Valley Lakes. Getahun and Stiassny (1998) compared the number of fish species reported in five drainage basins and the Rift Valley Lakes during the period 1835 to 1995 on basis of literature with the number of species collected during their own surveys during 1995-97. They reported a reduction in species numbers for each of the drainage basin varying from 40-85% and a reduction of species numbers for the Rift Valley lakes as a whole of ca. 65%. Ethiopia has a large variety of freshwater lakes, but except for Lake Tana and Lake Abaya fish communities were rarely studied in a quantitative way. Nine freshwater lakes were selected for a comparative study (see Zinabu Gebre-Mariam et al. 2002). These lakes show large differences in size (range: 20 - 3000 km 2) and productivity, and are located at altitudes varying from 1233 m to 2409 m above sea level (Table 1). The higher the altitude, the more temperate the climatic conditions are. None of these lakes are currently interconnected, but L. Chamo and L. Abaya (southern Rift Valley Lakes)
155 Ma nagement of shallow water bodies ..., EFASA 2010 were connected until a few decades ago and L. Ziway and L. Langano were interconnected in the geological past. The objective of this paper was therefore to give an overview on the fish species composition of nine Ethiopian lakes, threats of biodiversity and possible management measures.
Materials and methods The survey was carried out in the dry season during four field trips in the period 15 November 2004 and 20 January 2005. We selected 3 lakes in the highlands of Ethiopia in the North-West and 6 in the Rift Valley in the South (Fig. 1). The physical parameters were measured between 09:30 and 13:30 at three sampling sites in the openwater zone. Water samples were collected just below the surface at a depth of ca. 0.5 m and were pooled before filtration. All measurements were carried out in triplicate. Water temperature was measured at 1 m intervals over a vertical transect from just below the surface to 10 m depth (or less when depth was < 10 m). Ash weight was measured as an estimate of silt load. Light penetration in the water column was determined with a standard Secchi-disk (25 cm in diameter). Depending on seston and silt concentrations 250-900 ml of lake water was filtered through Whatman GF/C filters. Ash weight was determined by collecting seston and silt on pre-washed and pre-weighted filters. After collection the filters were dried and weighted on a microbalance, then the contents on the filters were ashed in an oven at 550 oC for 24 h and weighted again on a microbalance. Filters with chlorophyll were stored in a freezer for 5-15 days. As extraction solvent acetone was used; the absorbance of the centrifuged extract was then measured spectrophotometrically before and after acidification (ISO 1992). Fishes were sampled at two stations (one inshore, one openwater) during three successive days and nights. Gill nets of varying mesh sizes were used: one multi-mesh monofilament gillnet with small mesh sizes (5, 8, 10, 15 and 19 mm bar mesh) and one multifilament gill net with large mesh sizes (25, 30, 38, 45 and 55 mm bar mesh). The panel length of each mesh size was 15 m. In the shallow inshore stations one set of two multi-mesh nets were set: one net with small meshes and one with large meshes, whereas in the deeper openwater four nets were set (one set at the surface and one set at the bottom). When the water depth was more than 10 m the bottom nets were set between 7 and 15 m. Nets were set just before dusk; the exposure time was 2 h for the small meshed net and 15 h for the large meshed net. The Fisheries Effort per lake was 2025 m 2 net-hours for the small meshed nets and 15188 m 2 net-hours for the large meshed nets; Catch Per Unit Effort (CPU) was expressed as catch per 100 m 2 net per hour. A total of 22305 fish specimens were caught.
Ashe L. L.
Koka L. L. L. L.
L.
Fig. 1 : Map of Ethiopia showing the location of all nine study lakes (modified from Map UN-OCHA, United Nations, 2006)
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Results Physical parameters and chlorophyll : Water temperatures varied between 19 and 26 oC, with the lowest values observed in the mountain lake Ashenge (altitude 2409 m) in the north, and the highest temperature in L. Chamo (altitude 1233 m) in the south. L. Tana and Koka Reservoir showed relative low temperature values whereas the lakes in the Southern Rift Valley showed higher values. The northern crater lake, L. Hayk, in the highlands showed a surprisingly high water temperature (altitude 2030 m). This may have been the result of volcanic activity. Sediment load was high in Koka Res. and Lakes Ziway, Langano and Abaya. Secchi-disk depth varied between 6.5 and 0.1 m. The highest values, indicating high water transparencies, were observed in two northern lakes, L. Ashenge and L. Hayk, the lowest in some of the Rift Valley Lakes (Ziway, Langano and Abaya) (Figure 2 a,b,c). Chlorophyll concentration (content) varied between 1 and 83 µg l -1. The highest values were observed in the Rift Valley Lakes, the lowest in the two northern crater lakes (L. Ashenge and L. Hayk). L. Langano showed a very low chlorophyll concentration in combination with a low Secchi-disk depth, indicating a high silt load. The position of L. Tana was intermediate between the northern crater lakes and the Rift Valley Lakes (i.e. mesotrophic).
Fig. 2 : Environmental parameters showing: a) Water temperatures, b) Sediment load and c) Secchi-disk depth in the nine study lakes Fish communities: In total, 27 species were identified from the 9 lakes, but only 14 species were common or abundant (i.e. relative densities > 1%) (Table 1)). Based on the common and abundant species, the fish communities showed large differences in their species composition, there was only one exception. L. Abaya and L. Chamo were similar: the same larger fish spp. ( Synodontis schall , 157 Ma nagement of shallow water bodies ..., EFASA 2010
Hydrocynus forskahlii ) dominated in both lakes. The high similarity between L. Chamo and Abaya is not surprising because both lakes are bordering each other and were, until recently, interconnected. All other lakes are isolated and were not connected with each other in historic times. Lake Tana harboured the largest number of endemic species (n=17). The Labeobarbus species flock in L. Tana is dominated by the endemic L. brevicephalus (Table 1), whereas the in Ethiopia widely distributed L. intermedius is sub-dominant. The three Garra spp., of which two are endemic, were dominated by G. tana . Most fish species were observed in only 1 or 2 lakes. However, 5 species occurred in 3 or more lakes. These were Oreochromis niloticus (Nile tilapia), Labeobarbus intermedius (common large barb), Clarias gariepinus (African catfish), Garra dembecha , and Cyprinus carpio (common carp). With the exception of L. Tana all fish communities showed a low species diversity. The biodiversity was much influenced by rare (i.e. relative densities < 1%) species. If we exclude the species present in densities < 1%, all lakes including L. Tana showed a low fish species diversity. Especially small barbs ( Barbus amphigramma, B. humilis, B. paludinosus, B. tanapelagius ) reached very high relative densities in L. Tana, L. Hawassa and L. Ziway (92-98 % of the total catch) and substantial relative densities in L. Langano (ca. 35 % of the total catch). The small Garra from L. Ashenge and Koka Res. reached also relatively high densities (80-88% of the total catch), whereas L. Hayk contained substantial densities of Garra (ca. 25%). The size composition of the Nile tilapia ( O. niloticus ) was very different in L. Ashenge as compared to L. Hayk. In L. Ashenge we caught predominantly large tilapia (average weight 150 g) and in L. Hayk mainly small ones (average weight 15 g) were caught. L. Langano was characterised by a relatively high abundance of small Nile tilapia (O. niloticus ) and small Garra spp. The catfish (Synodontis schall ) which is dominant in L. Chamo (80% of the total catch) is a relatively large fish (average weight 125 g) and present in substantial numbers in Lake Abaya. In both lakes the tiger fish (Hydrocyon forskalii ) is also abundant. On basis of the average fish weight three different categories of fish communities can be distinguished: 1) fish communities with a very small average weight which are dominated by small Barbus spp. (i.e. in L. Tana, L. Ziway and L. Hawassa), 2) fish communities with a small to moderate average weight which are either numerically dominated by small Nile tilapia or by Garra (i.e. in L. Ashenge, L. Hayk, Koka Res. and L. Langano), and 3) fish communities with a relatively large average fish weight in which Synodontis schall is either dominant or present in relatively large numbers (i.e. L. Abaya and L. Chamo). We found a significant linear relationship (R 2= 0.50, P < 0.05) between chlorophyll concentration and catch per unit effort (CPUE, kg), but there were 3 outliers. In Koka Res. and L. Abaya the fish catch was lower and in L. Chamo higher than expected. The two northern crater lakes (L. Ashenge and L. Hayk) are oligotrophic and have as expected a very low CPUE.
Table 1 : Fish species with its abbreviations caught in the nine study lakes indicating in how many lakes a species was observed and in which lakes. Abbreviations used: ♦: introduced exotic species, AS: L. Ashenge, HA: L. Hayk, TA: L. Tana, KO: Koka Reservoir, ZW: L. Ziway, LG: L. Langano, AW: L. Hawassa, AB: L. Abaya, CH: L. Chamo
No. of Short Lakes in short Species Family lakes form form Observed Bagrus docmac BD Bagridae 2 CH, AB Barbus amphigramma BH Cyprinidae 1 AW Barbus humilis BH Cyprinidae 1 TA Barbus paludinosus BP Cyprinidae 2 ZW, LG Barbus tanapelagius BT Cyprinidae 1 TA Clarias gariepinus CF Clariidae 6 HA, TA, KO, ZW, LG, AW Cyprinus carpio ♦ CC Cyprinidae 3 HA. KO, ZW Garra dembecha GD Cyprinidae 5 HA, TA, KO, 158 Ma nagement of shallow water bodies ..., EFASA 2010
No. of Short Lakes in short Species Family lakes form form Observed AW, ZW Garra ignestii GI Cyprinidae 1 AS Garra regressus GR Cyprinidae 1 TA Garra tana GT Cyprinidae 1 TA Hydrocynus forskahlii TF Characidae 2 AB, CH Labeobarbus acutirostris LA Cyprinidae 1 TA Labeobarbus LB Cyprinidae 1 TA brevicephalus Labeobarbus. gorgorensis LG Cyprinidae 1 TA Labeobarbus intermedius LI Cyprinidae 7 TA, KO, ZW, LG, AW, AB, CH Labeobarbus longissimus LL Cyprinidae 1 TA Labeobarbus LMA Cyprinidae 1 TA macrophtalmus Labeobarbus megastoma LME Cyprinidae 1 TA Labeobarbus nedgia LN Cyprinidae 1 TA Labeobarbus truttiformis LT Cyprinidae 1 TA Lates niloticus NP Centropomidae 1 AB Oreochromis niloticus ON Cichlidae 7 AS, HA, TA, KO, ZW, LG, AW Schilbe intermedius SI Schilbeidae 1 AB Synodontis schall SS Mochokidae 2 CH, AB Tilapia zillii ♦ TZ Cichlidae 1 ZW Varicorhinus beso VB Cyprinidae 1 TA
Conclusions Biodiversity of the fish fauna of the two northern crater lakes, L. Ashenge and L. Hayk is low, but is limited by natural causes (i.e. high altitude and small lake size). L. Tana has a high biodiversity which is close to what is predicted for an African Lake of this size and altitude. The Koka reservoir, L. Ziway, L. Langano and L. Hawassa have low biodiversity, much lower than what could be expected on the basis of lake size and altitude. Although the fish fauna of Lakes Abaya and Chamo have higher species diversity than the more northern Rift Valley Lakes, their diversity is lower than expected on the basis of their size and altitude. In most water bodies, size composition of fish fauna seems to be directly affected by overfishing. By reducing stocks of target species (for food) like Nile tilapia and Labeobarbus spp., small fish species with a low economical value such as small Barbus spp. could become dominant. Ethiopia should clearly develop guidelines and directives for the gazetted fishery legislation and implement it through an enforcement agency. It would be advisable to regularly monitor the fish communities and the fisheries activities (catch-effort analyses) in the lakes as tools to improve the fisheries management in the Ethiopian lakes. High sediment loads in most Rift Valley Lakes lead to low fish stocks. It would, therefore, be advisable to reduce erosion in the catchments by replanting trees and enforce regulations protecting the vegetation in these areas.
References Getahun, A. and Stiassny, MJ (1998): The freshwater biodiversity crisis: the case of the Ethiopian fish fauna. SINET: Ethiopian Journal of Science 21: 207-230
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Leveque, C. (1995) Role and consequences of fish diversity in the functioning of African freshwater ecosystems: a review. Aquatic Living Resources 8: 59-78 Teferra, S. (1994) Basic facts about the population of Ethiopia and its needs . In: Panel on population-resource balance, The Biological Society of Ethiopia. Faculty of Science, Addis Ababa University, June, 1994, pp. 20-29 Thomas, CD (1994) Extinction, colonisation and metapopulations: environmental tracking by rare species. Conservation Biol. 8: 373-378 Zinabu Gebre-Mariam (2002) The Ethiopian Rift Valley Lakes: Major threats and strategies for conservation . In: Tudorancea C and Taylor WD (eds) Ethiopian Rift Valley Lakes. Biology of Inland Waters Series. Backhuys Publishers, Leiden, The Netherlands, pp. 259-271 Zinabu Gebre-Mariam, Kebede-Westhead, E. and Desta, Zerihun (2002) Long-term changes in chemical features of waters of seven Ethiopian Rift-valley lakes: chemical characteristics along a salinity-alkalinity gradient. Hydrobiologia 288: 1-12
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Benthic macroinvertebrate metrics in relation to physico-chemical parameters in selected rivers of Ethiopia
Getachew Beneberu 1 and Seyoum Mengistou 2 Bahir Dar University, Department of Biology, e-mail: [email protected] 1 Department of Biology, Addis Ababa University 2
Introduction Streams and rivers supply water for domestic uses, agriculture, transport, industries, power production and recreation. Their importance becomes more pronounced in developing countries especially in rural areas where they are major sources of drinking water without any form of treatment. In contrast to urban areas, they serve as receivers of untreated industrial, municipal, clinical and other types of liquid wastes and solid wastes. A considerable amount of waste ends up in open dumps or drainage system, threatening both surface water and ground water quality. Among the aquatic environments, rivers are widely used as disposal sites. A simple observation around rivers bank in the country indicates that a large percentage of uncontrolled waste goes directly to the rivers without any treatment. Although there is some sort of decree in the country that prohibits people from disposing waste along roads, avenues, rivers, ponds, and other sites, the regulation is continuously violated by people due to lack of alternative means for disposal (Taddese Kuma, 2004). This may be one possible reason why some of our river basins, particularly those which are near cities, are prone to severe degradation. The health of streams and rivers can be influenced by different factors such as geomorphologic characteristics, hydrological, chemical and physical water quality. However, together with these natural factors, the combined influence of urban development, pollution, bank erosion, deforestation and poor agricultural practices are the major degrading factors of running waters (Davies and Day, 1998). Ethiopia, a country which is known as the” water tower of Africa” is hydrologically divided into 12 Basins. Eight of these are River Basins, one Lake Basin and three Dry Basins. Four of the River Basins, Abbay, Baro-Akobo, Mereb and Tekeze are part of Nile River System, flowing generally in the western direction toward Sudan, eventually terminating in the Mediterranean Sea. Five Basins namely, the Omo-Ghibe, Awash, Rift-valley Lakes, Denakil and Aysha can be categorized as the Rift-valley system as all of them drain their water in the Great East African Rift-valley. The remaining three, Genale-Dawa, Wabishebelle and Ogaden are part of the Eastern Ethiopian Basin that generally flows in the south-easterly direction toward the Somali - Republic and then to the Indian Ocean (Ministry of Water Resources, 2007). The Abbay Basin is the most important Basin in Ethiopia by most criteria as it contributes about 45% of the countries surface water resources, 25% of the population, 20% of the landmass, 40 % of the nation’s agricultural product and most of the hydropower and irrigation potential of the country. Population density is highest in Rift Valley Lakes Basin indicating the immense pressure on the resource base. This is an indicative that the basins situated in an area where there is urbanization and industrialization are susceptible to environmental degradation The basin with the lowest population size and density is the Aysha Dry Basin mainly due to its remoteness, inaccessibility, harsh environmental condition and low resource potential and shortage of socio-economic infrastructures and services (Ministry of Water Resouces, 2007).The present study was done on three rivers which are located on the rift valley lake basins and Blue nile basin. The rivers are Meki and Tikur wuha. They were selected on the assumption that they were susceptible to pollution. Since benthic macroinvertebrate assemblages are more homogenous within a given ecoregion than among different ecoregions (Moog, et al ., 2004), the present study aims to characterize benthic- macroinvertebrates in the streams and rivers of Rift Valley Lakes Basin. The ecoregion concept provides a geographic framework for efficient management of aquatic ecosystems and their components (Hughes et al ., 1986). The delineation of ecoregions is based in patterns in geology, soils, geomorphology, dominant land use, altitude, natural vegetation, climate and wild life. One of the
161 Ma nagement of shallow water bodies ..., EFASA 2010 values of the ecoregion concept in river management is that it provides a rational basis for setting regional rather than national river water-quality standard. Benthic macroinvertebrates are an important part of river ecosystems. Stream dwelling invertebrates respond’ to changes in the physical and chemical environment. Benthic macroinvertebrates generally inhabit a localized area of a stream throughout their life cycle. Therefore, the individual organisms are continually exposed to many changes that occur in the chemical and physical environment. Collecting macroinvertebrates can provide an understanding of a river's condition. Because many macroinvertebrates live in the stream year-round and sometimes over multiple years, their presence or absence provides valuable information about a river's health over time. Knowledge of the ecological requirements of aquatic organisms, especially the benthic forms, is of outstanding importance to biologists in determining the degree and extent of pollution in streams. An examination of bottom fauna serves to indicate conditions not only at the time of examination but also over considerable periods in the past (Ferrigton et al , 1999). Those organisms having an annual life cycle will by their presence or absence indicate any unusual occurrence which took place during several previous months. Satisfactory use of aquatic organisms as indicators of pollution and self-purification of water is dependent upon knowledge of the normal habitats of these organisms and their sensitivity to varying environmental factors such as pollution. Generally speaking biological organisms can strengthen the information obtained through chemical analysis as every organism has a particular environmental requirement for it to be healthy and reproduce successfully. The presence or absence of healthy populations of organisms within their habitat is a sign of particular environmental characteristics (Mackie, 2001). Because of its limitation in some aspect and high cost, in recent years there is a shift in emphasis towards the development of more holistic measures of assessing aquatic ecosystem condition than simply physico-chemical parameters. For this purpose, benthic organisms are good candidates. By studying the community structure or the composition of benthic organism, it is possible to tell the quality of the water. For instance if pollution is severe, or is moderate but sustained over time, the whole community structure may simplify in favour of tolerant species (Rosenberg and Resh, 1993). Some groups are dominant in clear water and others in severely polluted waters. Insects like stonefly larvae, dobsonfly larvae, snipefly larvae, water spiders, mayflies, caddisfly larvae, and crustacean scuds prefer clear and well oxygenated water. Their number declines as the quality of the water deteriorates (Cummins, 1973). Oligochaetes, chironomids, lunged snails, blackfly larvae, leeches, and Physa sp. on the other hand are pollution tolerant, and hence they have indicator value for high load of organic pollution. Basically speaking biomonitoring provides a quick, pertinent overall environmental picture. This information is important to people who make management decisions aimed at maintaining and protecting the quality of rivers and streams. Biomonitoring is particularly valuable for alerting people to deteriorating aquatic conditions just as canaries alerted miners to deteriorating air conditions in the past . Most of the studies carried out in the country focus mainly on the lentic ecosystem, giving less attention to the riverine ecosystem. Almost this part of the aquatic system is untouched and is open to research. Some of the pioneers who worked on macroinvertebrates in Ethiopia include Harrison and Hynes (1988), Tesfaye Berhe (1988), and Worku legesse et al . (2004). Detailed and thorough study on benthic- macroinvertebrate structure in relation to environmental degradation is that of Baye Sitotaw covering four different basins (2006). Although Ethiopia is recognized as a classical example for its contrasting landscape and biodiversity, attempts to explore its river biota are almost non-existent. This lack of information precluded potential use of macroinvertebrates as indicators of water quality, making biomonitoring programs a remote possibility to the nation (Worku Legesse et al , 2004). Thus the general objective of this study was to assess the possibility of using macroinvertebrate assemblage and diversity as indicators of ecological water quality classes in some rivers in Ethiopia. Specific Objectives • To assess benthic macroinvertebrate structure in relation to physico-chemical parameters and habitat degradation in some streams and rivers. 162 Ma nagement of shallow water bodies ..., EFASA 2010
• To develop benthic macroinvertebrate metrics that characterize the ecological water quality class of rivers • To promote use of similar technique for other river basins and ecoregions in Ethiopia
Materials and methods Site selection : The study was conducted on three rivers .Two of the rivers namely Meki and Tikur wuha are part of rift valley lake basins, and the other one (Chacha) is part of the Blue Nile basin. In all except Tikur wuha two sites were selected one located downstream of the bridge and the other one upstream of the bridge. On Meki River the downstream site is near the bridge and is designated as near bridge site (Nb), and the second one was located far away upstream of the bridge and locally known as Jelu, which was abbreviated in this paper asJ. The second river studied was Tikur wuha (Tw). Since this place is highly marshy or swampy area, it was difficult for sampling, so only areas near the bridge were sampled. In this river, samples were taken downstream of the bridge. For River Chacha, the site upstream of the bridge was designated as C1 and the downstream site as C2. Throughout the paper, the above abbreviations will be used. Pre-classification of sampling sites : Prior to sampling pre-classification of the sampling sites were carried out, based on acceptedocol for pre-classification scheme, which is based on both environmental and biotic features such as sensory features (suspended solid, color, foam, odor and waste dumping and the like), periphyton, fungi, and dominance and occurrence of macroinvertebrates (Table 1). Based on the above information, sites were assigned to one of the five different water quality classes. The five water quality classes are: High or reference condition (Class1), Good (Class 2), Moderate (Class 3), Poor (Class 4) and Bad (Class 5). This part is important since it enables comparison between the above pre-classified sites with the actual measurements of physico-chemical parameter and benthic macroinvertebrate assemblage. Since most of the criteria used for pre-classifying the sampling sites were very subjective and also required great experience, only those criteria which could be used without any ambiguity were selected. Based on the aforementioned features, four water quality classes were identified. Two of the sites fall into good ecological state (class 2), one site is of moderate ecological status (class 3), one site fell to both moderate ecological status (class 3) and poor ecological status(class 4) , and one site was of bad ecological status (Class 5). Unfortunately there was no site that corresponds to the first water quality classe; as a result there is no reference site. Therefore the sites named as C1 and C2 corresponds to the second water quality class. The site Jelu (J) corresponds to the third water quality class, the site named as near bridge (Nb) corresponds to either the third or fourth water quality class, and finally the site named as Tikur wuha (Tw) corresponds to the fifth water quality class.
Table 1 . Decision support table for pre-classifying rivers into different water quality classes (modified after Aschalew, 2007) How to use the table + Or – indicates for the presence or absence of features or characters under study. Each one has got a score of 1, ++, a score of 2, +++ a score of 3 and it goes like this. Some of the score allocations were modified; a bit differ from the original table used. Some of them are highly subjective. For instance for some characters a percentage or words such as few, many, and very many are used. The modification was done with out affecting the magnitude of the original value.
Water quality classes Sensory features I II III IV V Non natural turbidity, suspended solids + + ++ Non natural color + + + ++ Foam + + + + Odour (water) + ++ ++ ++ Waste dumping + + + + Benthic macroinvertebrates 163 Ma nagement of shallow water bodies ..., EFASA 2010
Water quality classes Sensory features I II III IV V Dominance of extremely tolerant organisms (1-2) +++ Dominance of tolerant organisms (3-4) + ++ + Dominance of sensitive organisms(6-8) + +++ + Dominance of very sensitive organisms(9-10) +++ Species richness ++++ +++ ++ + + Chironomids with red color + ++ +++ +++++ Hydrophysidae + ++ ++ + Baetidae + ++ ++ + Sum of columns
In-situ physico-chemical measurements : Some physico-chemical parameterts were measured on site. Electrical conductivity was determined using a field conductivity meter. pH of the water was measured using portable digital pH meter. Dissolved oxygen and temperature were measured using Oxygen_ temperature analyzer with probe and cable. Chemical analyses : Before analysis, samples were first filtered through glass fiber filters (GF/C). The filtered water sample was used for measurement of some chemicals like (NO3-N), nitrite (NO2-N) and phosphate (PO4-P). For all measurements, a stock solution, intermediate and finally a serially diluted known concentration of working solutions were prepared and the absorbance was measured using spectrophotometer. The absorbance of the sample was measured at 420 nm for NO3-N, at 543 nm for NO2-N and at 885 nm for PO4-P. Based on the equation which was derived from the calibration curve the concentration of the unknown sample was extrapolated. Sampling of macroinvertebrates , sampling frequency and habitat selection: Sampling was carried out twice one during the dry season and the second during the wet season of the year . Unfortunately during the dry season, there was an unexpected heavy rain throughout the country, and in fact the rivers attained maximum volume and maximum depthas that expected during the rainy season. So the first sampling could be considered as wet season and the second as dry season. The abundance and diversity was high during the first sampling (wet season). In many studies the standard or the protocol for the length of the reach to cover is approximately 40x of the channel width (Gretchen, 2007). But some workers recommend to take about 100 m as a standard reach length. Since the rivers in the present study had an average width of greater than 18 m, it was very difficult to use and apply the above recommended standard protocol of reach length selection (40x of the channel width). As a result, it was preferable and practical to take about 100 m reach length as this length is easy to manage. In fact, the season of sampling can also give some clues on length reach selection. During the rainy season, the width of the river increases as a result it is difficult to use the standard method, whereas during the dry season, most of the rivers become dry or decrease their volume, in such cases it is possible to apply the standard protocol. Beside this, on all sites the different habitats available were identified. This is important since it enable us to select the appropriate sampling technique. Sampling technique: Several methods for collecting macroinvertebrates are available, and determining the most appropriate method depends on the goals of the objective of the study and the physical nature of the stream’s habitat. Because macroinvertebrates are not evenly distributed within a stream, multiple samples should be taken with any method to ensure adequate spatial representation of the stream reach. Taking this into consideration, multihabitat approach was employed. This is appropriate for those which are dominated by sandy or silt sediments or with variable habitat structure. Sampling was always started from downstream and then went upstream, in order to avoid disturbance to the sites . From the different habitat type identified samples were taken either through a Surber or a net depending on the type of habitat and finally samples were pooled together tp foem a composite sample. After sampling the samples were separated from other debris and preserved in 70 % ethanol and were taken to the laboratory for identification. Identification was done using various keys such as Pinder, (1978), Macan, (1973), and Edington and Hildrew, (1981), Cranston, (1982), Sahin, (1991), and Epler, 164 Ma nagement of shallow water bodies ..., EFASA 2010
(2001). After identifying the samples to the family level, each family was counted and percentage composition was calculated. Data analysis : One of the commonly used biotic metrics, Shannon-Wiener index was calculated for each site based on data from the macroinvertebrate assemblage. Beside this, the commonly applied scoring systems such as BMWP (Biological monitoring Working Party), NEPBIOS (Nepalese Biotic score), SASS (South African Scoring system) and Hilsenhoffs family biotic index (HFBI) were determined for each site. These scoring systems differ in their allocation of tolerance values (Appendix 1 and 2). One important use of this scoring system is that it could give some information about the quality of the water. It means that in the reference or less impacted sites, the diversity is very high; as a result most scoring systems will end up with highest total scores. When the degree of pollution increases, this will decrease the diversity, and consequently the number of families and total scores will become low. Statistical analysis: For basic metric calculation, a simple Excel sheet was used. The data was analyzed statistically using SPSS version 15 and PCA was also done.
Results Temperature: Though there was no significant difference in temperature in all sites, the average temperature was relatively higher at Nb site than the other sites both during the first and the second sampling period (23. 83 - 25.4 0C). The average temperature in the other sites ranges from 19.23- 25.27 0C at J site, 2 2.2 - 23.7 0C at Tw site. In Chacha river sampling was done only ones and the average temperature for C1 was 21.7 0C and 22.75 0C for C2. In those sites where sampling was done twice, the maximum temperature was recorded during the first sampling period. Dissolved oxygen (DO): The amount of dissolved oxygen was much lower at site Tw than the other sites. High amount of dissolved oxygen was recorded from Chacha River at site C2. Dissolved oxygen varied over the study period from 6.04 - 6.22 mg/L, 6.35-6.42 mg/L,6.49-6.71 mg/L and 12.4-13.66 mg/L at J, Nb, C1 and C2 sites respectively. At (Tikur wuha, t dissolved oxygen was not measured first sampling period. But the dissolved oxygen measured during the second sampling was very high. and reached values less than 0.93 mg/L and at some points. alues over 2.23 mg/L. Though there was data on dissolved oxygen during the first sampling period, the benthic fauna of Tikur wuha was mainly dominated by chironomids (red in color all). Of the two sites in River Meki, the second site Nb had lower concentration of dissolved oxygen (5.27 mg/L) than the first site j, with concentration of about (6.84 mg/L). Conductivity and pH : In terms of conductivity Tw had a higher conductivity (almost three fold) than the other sitesComparison was made between Lake Hawassa and its tributary, Tikur wuha. In fact Tikur wuha had a higher conductivity than the lake itself. The maximum conductivity for Tw was 911 ms/cm. The conductivity at site J ranged from 247.6 to 245 µs/cm and at Nb site from 320 to 324.3 µs/cm. Conductivity at Nb site was higher than at J site. In all sites higher conductivity was measured during the first sampling period. The pH over the study period varied from 7.8-7.93, 7.83-7.85, 7.65-7.67, and 8.34-8.37 and 8.4-8.77 at site J, Nb, and Tw, C1 and C2, respectively. There was no significant difference in pH in the three sites, though the pH seems a bit higher at site C1 and C2. Nutrients: The concentration of nitrite over the study period varied from 7.56 - 15, 5.44 - 13.33 and 6.78 - 11.08 µg/L at site J, Nb, and Tw, respectively. The concentration of nitrite at C1 and C2 was 13.20 µg/L and 14.66 µg/L, respectively. Highest value (15 µg/L) was recorded at Jelu during the first sampling time. Soluble reactive phosphate varied from 36.81 - 39.89, 45.37 - 49.21 and 14.35 - 61.75 at site J, Nb, and Tw, respectively. C1 and C2 had a phosphate concentration of 27.54 µg/L and 18.12 µg/L, respectively. The highest and lowest value was recorded at site Tw. On an average the amount of soluble reactive phosphate was high at site Nb. The average concentration of nitrate was 63.54, 25.42, 50.83, 127 and 222 µg/L at site J, Nb, Tw, C1 and C2, respectively. Chacha River had a highest amount of nitrate as compared to others. In fact high concentration of nitrate was recorded at site C2 (Table 2). Table 2 : Mean values of some physico-chemical parameters in the five sites studied (pH in scale, conductivity in µs/cm, Dissolved oxygen in mg/L, nutrients in µg/L and temperature in 0C)
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Water Parameters quality pH Conductivity DO N-NO N-NO P-PO Temperature class 3 2 4 WQ3 7.86 246.3 6.49 63.54 11.28 38.35 22.25 WQ4 7.84 322.15 5.83 25.42 9.39 47.29 24.61 WQ5 7.66 911 1.00 50.83 8.93 38.07 22.95 WQ2 8.35 320 6.59 127 13.20 27.54 21.7 WQ2 8.36 318 12.82 222 14.66 18.12 22.75
Benthic macroinvertebrate assemblage : A total of eleven families were identified during the study period (Table 3). Almost all except two families (Notonectidae and Tipulidae) were present at site C2.Among the 11 families only four were present at Nb site and only 3 families were found at Tw site. The site C1 is rich in number of family next to C2. The diptera, Tipulidae was the only family recorded at site J. Planorbidae, Sphaeridae and Hirudinea were found only at cite C2. In sites J, Nb, and Tw more than 50 percent of the benthos was contributed by the dipteran Chironomidae. The percentage composition of Chironomidae at the two sites of Meki River was more or less similar, 54.4 % at J and 47.88% at Nb site. The highes percentage was found at Tikur wuha with Chironomidae contributing more than 94.5 % of the benthic fauna. At site C1 the highest contribution came from the Odonata (Coenagrionidae) followed by Ephemeroptera (Baetidae). At site C2 the highest contribution comes from two groups of Ephemeroptera (Baetidae and Caenidae). In general the family Chironomidae was the dominant benthos followed by Hydropsychidae and Baetidae, and the least contribution came from Tabanidae, Corixidae and Notonectidae at J site. At Nb site both Chironomidae and Batidae had almost equal contribution while the least contribution was of Corixidae and Hydropsychidae. Almost 95 % of the benthos at Tw site was represented by Chironomidae. Baetidae and Notonectidae on the other hand contributed the least (Fig.1).
Table 3. Percentage composition of benthic macroinvertebrates among sites
Benthic macroinvertebrates Sites Taxa list J NB Tw C1 C2 Ephemeroptera (Mayflies) Baetidae 17.27 46.47 4.05 14.06 24.67 Caenidae - - - - 20.83 Hemiptera (Water or true bugs) - - - - - Corixidae (waterboatmen) 1.81 4.22 - - 12.82 Notonectidae (back swimmers) 3.63 - 1.35 9.375 - Odonata (Damselflies andDragonflies) - - - - - Coenagrionidae - - - 64.06 1.92 Trichoptera (Caddisflies) - - - - - Hydropsychidae 17.27 1.40 - - 1.60 Unidentified - - - - 0.32 Diptera (Two winged or''True flies'') - - - - - Chironomidae 54.4 47.88 94.5 3.125 17.62 Tipulidae 5.45 - - - - Mollusks(Snails) - - - - - Planorbidae - - - 9.375 3.52 Sphaeriidae - - - - 2.88 Hirudinea(Leeches) - - - - 6.41
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Fig. 1 : Percentage composition of benthic mcroinvertebrates at different sites: (a) J, (b) Nb, (C) Tw, (d) C1 and ( e) C2 sites
Diversity index and scoring systems Shannon-Wiener diversity index is one of the indices which is commonly used to assess differences in species composition between different habitats. Though the results of the Shannon-Wiener index needs to be used with caution, it is still a good tool for comparing two distinct habitats. One of the drawback of this index is it doesn’t take into account habitat specific parameters required by specific species. Beside Shannon-Wiener diversity index several scoring systems were calculated for each site. Among these the followings were used (BMWP, SASS, NEBPIOS, and HFBI). (Table 4).
Table 4 . Calculated diversity and scoring values for the five sites
Shannon Site and HFBI BMWPB NEPBIOS ASPT- ASPT- ASPT- name weaver SASS diversity BMWP NEPBIOS SASS index Je 1.29 6.46 25 29 23 4.17 4.83 3.83 Nb 0.90 6.42 16 18 15 4.00 4.50 3.75 Tw 0.24 7.83 10 11 9 3.33 3.67 3.00 C1 1.15 7.20 20 20 16 4.00 4.00 3.2 C2 1.91 6.34 59 42 31 6.55 4.66 3.87
Average score per taxon was also calculated (ASPT) for the first three scoring systems. It was calculated as the sum of the total score divided by the number of taxa or family present in the sample. Some workers argue that the ASPT is better than the total score as it is independent of sample size and perhaps less influenced by the season than the BMWP . 167 Ma nagement of shallow water bodies ..., EFASA 2010
Discussion In the present study, based on certain environmental and biotic features, sites under investigation were assigned to different water quality classes. Accordingly, two of the sites namely C1 and C2 were placed in water quality class II. The site J was placed in water quality class III, and the site Nb fell either to water quality class III or IV. The site that was placed to higher water quality class was Tw (water quality class V). In order to see which physico-chemical parameter would have a great discriminating power among sites principal component analysis (PCA) was done. The PCA result showed that the majority of the variation among sites was mainly due to four parameters. These were N-NO 2, N-NO 3, pH, and P-PO 4. In fact 71 % of the variation was explained by nitrite followed by nitrate (17.48 %). Both pH and Phosphate contribute about 11.03 % of the variation. Temperature and conductivity contributed the least to the variation among sites. Though the conductivity was extremely high at site Tw, its discriminating power was too poor according to the PCA loading result. This indicates that the presence of one or few parameters with unusual high values may not be important parameter for separating sites of different water quality classes. By using only nitrite as the first component (axes), it was possible to separate water quality class II and III from that of water quality class IV and V (Figure 2). Similarly by using the first and the third axes it was also possible to discriminate water quality class II and V from that of water quality class III and IV. An attempt was also carried to use the other axes namely axes 2 and axes 3. These two axes could potentially separate water quality class II and III from others by using only pH. (Figure 2).
WQ3 0.8 WQ2 0.6 WQ5 WQ3 1.6 Conductivity b 0.4 P-PO4 a 1.2 0.2
pH 0.8 p H -2.4 -1.6 -0.8 N-NO20.8 1.6 2.4 3.2 4 WQ2 -0.2 0.4 N-NO3 DO -0.4 N-NO3 N-NO2
N itra te -2.4 -1.6 -0.8 0.8 1.6 2.4 3.2 4 pH WQ2 WQ5 -0.6Conductivity -0.4 WQ3 WQ4 -0.8 WQ3 P-PO4 -0.8 -1 WQ2 DO Temperature Nitrite Temperature-1.2
WQ4 -1.6
-2 Nitrite
WQ3 0.8 WQ2 0.6 WQ3 c 0.4 P-PO4 0.2
pH pH -2 -1.6 -1.2 -0.8 -0.4 N-NO2 0.4 0.8 1.2 1.6 2 -0.2 DO -0.4 N-NO3
-0.6 Conductivity WQ5
WQ4 -0.8
-1WQ2 Temperature Nitrate
Fig. 2 . PCA scatter diagram: (a) axis 1 and 2, (b) axis 1 and 3, and (c) axis 2 and 3
As can be seen there is no a single parameter that could potentially discriminate all the sites, though the biggest variation among sites comes from nitrite. 168 Ma nagement of shallow water bodies ..., EFASA 2010
The concentration of nitrate was very high at water quality class II (C1 and C2). The unusual high concentration of nitrate in these two sites could be because of the different activities performed near the bank of the river. The Chacha river is used for various activities. People use the water for drinking, washing their clothes, bathing, and also for dumping of domestic wastes. In addition the water is mainly used for watering their cattles. The wastesf the cattle might be the major reason for high amount of nitrate in the river. This was not the case only for Chacha River; similar activities were also performed at Meki River. But the concentration of nitrate is not as such high as compared to C1 and C2. The average concentration of nitrate at site J was 63.54 µg/L and that of Nb was 25.42 µg/L. But the phosphate concentration was high at Meki than Chacha river. As opposed to Chacha river, Meki river is mainly used for washing as well as watering of livestock. The high concentration of phosphate at Meki River might be due to different detergents or soap used for washing purpose. Though the amount of dissolved oxygen was extremely low at water quality class V (at Tikur wuha), it was not possible to use it as discriminating parameters among sites. Its effect was similar with that of conductivity. Normally with deteriorating water quality, it is expected that the major concentration of nutrients will increase. Again such kind of trend was not observed in the present study, especially for nitrate. The amount of nitrate was high at water quality class II (C1, 127 µg/L and C2, 222 µg/L) than at water quality class V (Tw, 50.83 µg/L). Only the amount of phosphate was more or less comparable in all water quality class, though high amount was recorded at water quality class V. This is an indication that chemical analysis alone may not be good parameter to discriminate sites with different water quality classes. The other important feature dealt in the present study was the use of metrics and scoring systems. One metrics and three scoring systems were calculated for each site. In addition average score per taxon (ASPT) was also computed for some scoring systems. Among these parameters almost more than 97 % of the variation among sites was explained only by BMWP scoring system. The other scoring system namely NEPBIOS and SASS contributed 2.1625 % and 0.0619 %, respectively to the total variation (Figure 3). The remaining ones Shannon-Wiener index (S-W) and HFBI contributed less to the variation. As a result only the following three (BMWP, NEPBIOS and SASS) could potentially discriminates sites of different water quality classes. This was not possible through physico-chemical analysis. The three parameters (BMWP, NEPBIOS and SASS) are independent of individual taxa in the sample, whereas the other two (S-W, and HFBI) are dependent on individual numbers of taxa in the sample. In the present study both approaches meaning quantitative and qualitative techniques were employed. But in most sites the later one was frequently employed for reasons related to the presence of more pools than riffles or runs. Therefore the weak discriminating power of S-W and HFBI could be because of the aforesaid reasons. If only quantitative study was done a different trend might be obtained. Hence in the present study the S-W and HFBI are not powerful in discriminating sites of different water quality classes. On average higher BMWP scores was found for those sites of relatively in good condition (C1 and C2), whereas lower scores was found for sites with poor water quality (at Tw, water quality class V). Though the degree differed, the same trend was observed for the other two scoring systems (NEPBIOS and SASS). This is an important finding in that based on benthos (Index of Benthic Macro-invertebrates), it is possible to at least alert concerned bodies (government or other organizations) about the condition of the water body.
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J 5 HFBI 0.48 4 0.32 NEPBIOSSASS b Tw a 3 J NEPBIOS C1 0.16 2
-40C2 -32 -24 -16 -8 BMWP 8 16 24 1 S-W -0.16 SASS SASS NEPBIOS ASPT-NEPB Nb S-WASPT-SAS ASPT-BM -40 -32 -24 -16 -8 8 16 24 -0.32 ASPT-NEPB ASPT-BM C1 ASPT-SAS HFBI -1 -0.48 -2 -0.64 C2 -3 -0.8 Tw Nb BMWP-4 BMWP BMWP
HFBI 0.48
Tw 0.32 C1 NEPBIOS J 0.16
-4 -3 C2 -2 -1 BMWP 1 2 3 4 5 S-W -0.16 SASS SASS ASPT-BM -0.32 ASPT-NEPB ASPT-SAS
-0.48
c -0.64
-0.8 Nb NEPBIOS
Fig. 3 : PCA scatter diagram: (a) axis 1 and 2, (b) axis 1 and 3, and (c) axis 2 and 3
Regarding the benthic assemblage, the percentage of chironomid was very high at site Tw, followed by J and Nb sites. The least contribution came from sites C1 and C2. All in all the benthic fauna of Tw was mainly dominated by chironomids (red in color and perhaps chironomini spp). Though chironomids are highly tolerant to severe environmental degradation, there is an optimum value of DO for the survival of the group. During the first sampling period DO measurement was not taken at Tikur wuha site, but the abundance of benthos sampled was relatively high. It was surprising not to collect even a single benthic specimen during the second sampling period. One possible reason could be the limited amount of dissolved oxygen which was about 1.90 mg /l. Without DO benthic life was very threatened and only catfish was observed in the river. This is evident since most of the catch by the local people was mainly catfish. This fish has certain adaptation to live in such severely degraded environment. Beside it could move outside the river and enter into the lake when conditions became very harsh. The diversity of benthic macroinvertebrates in terms of family level was high at water quality class II followed by Water quality class III. Low diversity was evident at water quality class V. Highest % of EPT taxa (though there was no Plecoptera) was found at water quality class II and III. The lowest percentage of EPT taxa was recorded at water quality class V. The present study clearly showed that by monitoring benthic macroinvertebrates, it is possible to assess the quality of the water in the studied rivers. This could also be extended to other water bodies in the country. Finaly, the sampling technique had also its own drawback. Sampling with Surber becomes more effective and sound if the abundance or diversity of benthos is very high. Only few benthos were sampled during the study period. One possible reason could be the low diversity of benthic maroinvertebrates in the studied rivers especially that of Tikur-Wuha and Meki River, besides spatial variation, could be that only few sites along the reach were sampled. By chance we could have missed some of the sites which are dominated by benthos, as some groups are site and substrate-specific.
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References Aschalew Lakew (2007). Applicability of Bioassesment Methods using Benthic Macroinvertebrates to Evaluate the Ecological Status of Highland Streams and Rivers in Ethiopia. M.Sc Thesis, UNESCO- IHE Institute for Water Education, Delft, the Netherlands. Baye Sitotaw (2006). Assessment of Benthic- Macroinvertebrate structures in relation to Environmental degradation in some Ethiopian Rivers.M.Sc Thesis, School of Graduate Studies, Addis Ababa, University. Cummins, K.W. (1973).Trophic relations of aquatic insects. Ann.Rev of Entomol . 18 : 183-206 Davis, B.R. and Day, J.A. (1998). Vanishing Waters . University of Cape Town Press. Edington, J.M.and Hildrew, A.G. (1981). Caseless Caddis larvae of the British Isles. Fresh Cape Town water Biological Association, Scientific Publication No 43. Epler, J. H. (2001). Identification manual for the larval Chironomidae (Diptera) of Florida . Florida Department of Environmental Regulation. Tallahassee. Ferrington, L. C., Jr., Blackwood, M. A., Wright, C. A., Crisp, N. H., Kavanaugh, J. L., and Schmidt, F. J. (1991). A protocol for using surface-floating pupal exuviae of Chironomidae for rapid bioassessment of changing water quality. In Sediment and stream water quality in a changing environment: trends and explanations, IAHS , pp. 181-190. Gretchen, H. (2007. Methods for the collection and analysis of benthic macroinvertebrate assemblages in wadeable streams of the Pacific Northwest. Pacific Northwest Aquatic Monitoring Partnership, Cook, Washington Harrison, A.D. and Hynes, H.B.N. (1988). Benthic fauna of Ethiopian mountain streams and rivers. Arch.Hydrobiol/Suppl .81 (1):1-36 Hughes,R.M., Larson,D.P., and Omernik,J.m.(1986). Regional reference sites: A method for assessing stream potentials. Environmental management . 10 :629-635. Macan, T.T. (1979). A key to the nymphs of British Ephemeroptera . 3 rd ed. Freshwater Biological Association, Scientific Publication Mackie, G.L. (2001). Applied aquatic system concepts .Kendall/Hunt Publishing Company, 744 pp Ministry of Water Resources (2007). Nature and features of the Ethiopian River Basins.Web site last updated on: Sept 02, 2007 Moog, O., Schmidt-Kloiber, A., Ofenbock, T., and Gerritsen,J. (2004).Does the ecoregion approach support the typological demands of the EU ’ Water Framework Directive’? Hydrobiologia . 516 :21- 23 Pindler, L.C.V. (1986). Biology of freshwater Chironomidae .Ann Rev Entomo l. 31 :1-23. Rosenberg, D.M. and Resh, V.H. (1993). Freshwater Biomonotoring and Benthic macro- invertebrates . Chapman and Hall, New York 488 pp Tesfaye Berhe (1988). The Degradation of the Abo-Kebena River in Addis Ababa, Ethiopia.M.Sc thesis, School of Graduates Studies, Addis Ababa University. Tesfaye Berhe, Harrison, A.D.H. and Hynes, H.B.N. (1989). The degradation of a stream crossing the city of Addis Ababa, Ethiopia. Trop.Freshwat.Biol .2:112-120 Worku Legesse; Giller, P, S. and O’halloran, J. (2000). Physicochemical and Biological assessment of the Kebena River, Addis Ababa, Ethiopia. Department of Zoology and Animal Ecology, National University of Ireland, Cork
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Assessment of downstream dispersal of juveniles of the migratory riverine spawning Labeobarbus species of Lake Tana (Ethiopia)
Wassie Anteneh 1, Abebe Getahun 2 and Eshete Dejen 3 Bahir Dar University, College of Science, Department of Biology, Bahir Dar, Ethiopia; [email protected] 1 Addis Ababa University, Science Faculty, Department of Biology, Addis Ababa, Ethiopia 2, Food and Agriculture Organization (FAO), Addis Ababa, Ethiopia 3
ABSTRACT : Down stream dispersal, termed as drift, of juveniles of the unique species flock of the migratory riverine spawning Labeobarbus was investigated in Gumara and Gelda tributary rivers of Lake Tana in January 2008. Physico-chemical data and juveniles of Labeobarbus were collected from selected sampling sites at the river mouths and nearby stretches as well as in upstream sites (about 30 km far from the mouths) of each river. Juvenile Labeobarbus were collected using seines of 3 mm stretched bar mesh size and analysed in the laboratory. No juvenile labeobarbs was captured in all Gumara River sampling stations, instead we caught 308 small barbs and 5 Oreochromis niloticus, whereas, a total of 697 juvenile Labeobarbus were collected from Gelda River sampling stations. Of these 576 (82.6%) juveniles were collected from the river mouth areas, which may indicate that juveniles undergo some kind of acclimatization at this intermediate (riverine-lake) site before entering into the pelagic habitat. The total length of Juveniles ranged from 9 mm to 720 mm and the mean size was 204 mm. However, the mean total length of juveniles at the river mouth is 205 mm, which could be considered as the average size for juveniles to enter into the lake. The rivers were highly degraded. If the juvenile drift is the only form of recruitment, nursery habitat modification will result in the collapse of this endemic stock. Therefore, baseline data about the ecology and biology of juveniles is urgently needed in order to sustain the stock (since the present study can be considered as a reconnaissance survey) in order to carry out detailed investigation.
Key words : Downstream dispersal, Ethiopia, Labeobarbus , Lake Tana, migratory fishes.
Introduction Ethiopia is known for its enormous water resources potential. The total annual runoff is estimated to be about 110 billion m 3, and only less than 5 % is used in the country, the remaining leaves the country through trans-boundary rivers such as Blue Nile, Baro-Akobo, Wabi Shebele, Tekeze and Genale-Dawa. Blue Nile, the longest international river system in the world, provides 86% of the waters of the Nile River (Swain, 1997). This river originates from Lake Tana, the largest lake in Ethiopia and the third largest in the Nile Basin. Gilgel Abay, Ribb, Gumara, Gelda, Dirma, Arno-Garno and Megech are the main rivers feeding the lake which contribute more than 93 % of the inflow. However, the Blue Nile River is the only surface outflow for the Lake. The Lake is located in the north western high lands of Ethiopia at an altitude of 1800 m above sea level. It has a surface area of 3150 km 2, which is 50% of the total lakes’ area in the country. The Lake Tana Basin is rich in biodiversity with many endemic plant species, and cattle breeds; it contains large areas of wetlands; it is home to many endemic fish, birds and cultural and archaeological sites (De Graaf, 2003). Lake Tana is home to seven genera of fishes: Barbus , Clarias, Garra, Labeobarbus , Nemacheilus, Oreochromis and Varicorhinus . The genus Labeobarbus is considered as the largest and forms the only known intact endemic cyprinid ‘species flock’ in the world (Nagelkerke and Sibbing, 2000). The Lake Tana Basin is one of the most affected area by soil erosion, sediment transport and land degradation. The land and water resources of the basin and the Lake Tana ecosystem are highly impacted by the rapid growth of human population, deforestation and overgrazing, soil erosion, sediment deposition, storage capacity reduction, drainage and water logging, flooding, pollutant transport, and over-exploitation of the endemic fish species. De Graaf et al . (2004), using trawling catch in the lake, reported about 75% decline (in biomass) and 80% (in number) in adults and 90 % in juveniles of for some of the endemic species flock of Labeobarbus from Lake Tana, perhaps due to recruitment-overfishing . However, the exact driving force for the decline of the stock is still not clearly
172 Ma nagement of shallow water bodies ..., EFASA 2010 investigated. One most plausible explanation could be destruction of the nursery grounds of the juveniles of the migratory species of Labeobarbus . Although various studies have been made about the spawning migration of Labeobarbus species of Lake Tana to the tributary rivers (Nagelkerke and Sibbing, 1996; Palstra et al ., 2004; Wassie et al ., 2008), data about the ecology and biology of juveniles of the migrating Labeobarbus species of Lake Tana are totally absent. Therefore, the purpose of this study was to make a preliminary assessment about the downstream dispersal of juveniles of Labeobarbus species migrating to spawn in Gumara and Gelda tributary rives of Lake Tana. Objectives General objective : The objective of this study was to collect preliminary data about the juveniles’ ecology and biology of the Labeobarbus species from Gelda and Gumara Rivers, tributaries of Lake Tana, which can be used to propose a systematically designed and comprehensive further study. Specific objectives : • To assess whether juveniles of Labeobarbus stay in the spawning rivers during the dry season, • To characterize the habitats of juveniles, • To estimate the relative abundance of juveniles in the nursery rivers, • To determine the average size when they drift to the lake.
Materials and methods Study area : Lake Tana, the headwater of the Blue Nile River, is located in the northwestern highlands of Ethiopia (at an elevation of 1830 m). It is an oligo-mesotrophic shallow lake with an average depth of 8 m and maximum depth of 14 m. The lake is turbid, well-mixed and has no thermocline (Eshete Dejen et al ., 2004). Fogera (on the east) and Dembea (on the north) plains border major parts of Lake Tana, and they are considered to be the buffering zones of the lake (Nagelkerke, 1997). The lake is believed to have originated two million years ago by volcanic blocking of the Blue Nile River (Mohr, 1962). It assumed its present shape through blocking of a 50 km long quaternary basalt flow, which filled the exit channel of the Blue Nile River (Chorowicz et al ., 1998).
S2
S1
Fig. 1 . Map of Lake Tana and the study rivers (S 1 and S 2) (Map Modified from De Graaf et al ., 2003)
However, there are strong evidences that Lake Tana had dried up between 16000 and 50000 years ago (Lamb et al ., 2004). The catchment area of Lake Tana has a dendritic type of drainage network. More than 60 ephemeral and seven big perennial rivers flow into Lake Tana: Gelgel Abbay (the biggest), Gelda, Gumara, Rib, Arno- Garno, Megech and Dirma. However, the only out flowing river from Lake Tana is the Blue Nile (Fig. 1). Gelda and Gumara Rivers (Fig. 1) are approximately 60 and 105 km, long, respectively, During our
173 Ma nagement of shallow water bodies ..., EFASA 2010 sampling time (in January, which is in the dry season), Gumara River at its mouth was about 25 m wide and up to 2 m deep. The river bank at its mouth and upstream sites has no macrophyte coverage or riparian vegetation. The surrounding area is intensively cultivated for crop production by pumping water from the river. On average, in every 50 m there was one water pump. This pressure was not observed in Gelda River. During our sampling month (same month as in Gumara), Gelda at its mouth was about 20 m wide and 1.5 m deep. This river at its mouth is covered by macrophytes and the bottom is muddy. Although there are agricultural activities at its mouth and upstream sites, relatively the riparian vegetation is by far better than Gumara River. Both rivers flow about 30 km in the Fogera floodplain before joining the lake. These rivers flow in the Fogera floodplain very slowly. These slowly flowing river segment may serve as nursery ground for juveniles of Labeobarbus species of Lake Tana (Figure 2). Physico–chemical and other biological parameters : At all selected sampling sites, dissolved oxygen, temperature, pH, coordinate (GPS) and Secchi depth measurements were taken. Substrate type and macrophyte or riparian vegetation cover status of the sampling sites were described. The depth and width of the rivers at the sampling sites were also measured and the flow velocity of water was rated as fast, medium or slow by visual observation. Juvenile fish collection : Juveniles of Labeobarbus species were collected during daylight hours at selected sampling sites along Gumara and Gelda River mouth areas using a juvenile beach seine (length 10 m, depth 1 m, mesh size 2.0 mm). In each of these sites, the seine was dragged about 100 m length of the river. At the river mouth sampling areas the seine was pulled at one side by fiber motor boat and on the other side by two men. However, in the upstream sites since it cannot be reached by boat, the beach seine was pulled by only men. Moreover, in the upstream sampling sites, it was difficult to get 100 m long and 10 meters wide. Hence, we were forced to make some modifications on the size of the beach seine and area of sampling. In Gumara River upstream sites, the area we made our sampling was 300 m 2 (6 m wide and 50 m long), however, in Gelda upstream in each site, we seined only 90 m 2 ( 6 m wide and 15 m long). Juvenile densities were calculated based on these areas. Juveniles were fixed in 4% formaldehyde and transported to Bahir Dar Fish and Other Aquatic Life Research Center for laboratory analysis on the following day. Juveniles of Labeobarbus were identified (from adult small barbs) by observing the stiffness of the first dorsal spin. However, it was impossible to classify the juveniles into species since their size is smaller than 20 cm, hence all juveniles are lumped. Length and weight (using 0.01 electronic sensitivity balance) measurements were taken in the laboratory. Some representative specimens of juveniles of Labeobarbus were transported and preserved in Fisheries Laboratory of Department of Biology, Addis Ababa University for further future meristic and morphometric investigation. In addition to collecting juveniles with seine, information about the presence of juvenile fish in the sampling rivers was collected through interviewing some local farmers. This information was even very useful during the selection of our sampling sites.
Results and Discussion Physico-chemical (abiotic) parameters : Environmental factors such as dissolved oxygen, temperature, pH, vertical transparency (Secchi depth) are summarized in Table 1. Dissolved oxygen was highest in Gelda most upstream site (Gelda UPIV). The river at this site was relatively shallow and faster, this higher oxygen concentration is perhaps due to this higher flushing of the river at this site. Generally, the concentration of dissolved oxygen was lower in the Gumara upstream sites (Table 1) as compared to Gelda. The flow rate was very slow and the water was very turbid; this again can be substantiated from the lowest Secchi readings (Table 1). Temperature was highest at Gumara River mouth areas, most probably this high value is due to the difference in time of measurement. It was taken nearly at mid-day, whereas, it was before 10:00 AM in other sampling sites. The pH readings indicate also that the rivers are neutral to slightly alkaline.
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Table 1 . Abiotic parameters in the river mouths and upstream areas of Gumara and Gelda. (RM =river mouth, UP =upstream).
Distance from Coordinate Oxygen Temperatu Depth Secchi Sample Site pH mouth (km) (GPS) (mg/L) re (°C) (m) (cm) Gelda RM ------N11°42.2´72`` 6.3 19.8 1.5 40 7.35 E37°25.2´90`` Gelda UPI 1.5 N11°42.1´53`` 6.3 19.7 2 50 7.36 E37°25.6´35`` Gelda UPII 3.5 N11°43.8´80`` 6.3 19.5 2.1 50 7.66 E37°26´37`` Gelda UPIII 27 N11°43.4´43`` 6.4 21.7 Shallow Clear 7.34 E37°30´94`` Gelda UPIV 29 N11°43.4´73`` 6.5 21.6 Shallow Clear 7.31 E37°30.2´25`` -est Gumara RM ------N11°54´92´´ 6.3 20.1 2.5 40 7.54 E37°29.5´07´´ Gumara UPI 2 N11°53.9´56´´ 6.2 21.8 2 40 7.77 E37°29.9´72´´ Gumara UPII 7 N11°53.5´39´´ 6.2 21.2 3 60 7.95 E37°30.4´79´´ Gumara 30 N11°50.5´06´´ 6.1 16.1 0.5 30 7.35 UPIII E37°38´99´´ Gumara 33 N11°50.3´59´´ 5.9 19.1 0.6 35 7.83 UPIV E37°38.3´16´´
Gelda River Gumara River
Fig. 2 : Sampling along the Gelda and Gumara river mouths.
Juvenile fish composition in the river mouths and upstream areas: A total of 1732 fish specimens were collected from all the 10 sampling sites (Table 2) of the two rivers. Some of the juveniles were scaleless (larval stage). The three species of small barbs (mainly Barbus humilis) captured in the sampling sites contributed 55.77% (966 specimens) of the total catch in number, whereas, a total of 697 (40.24%) juvenile specimens of Labeobarbus were collected from all sampling sites (Table 5.2). The
175 Ma nagement of shallow water bodies ..., EFASA 2010 remaining 69 (3.9%) of the specimens belong to the genus Garra (55 specimens), Oreochromis niloticus (12 specimens) and L. intermedius (2 specimens). No juveniles of Labeobarbus were caught from all the five sampling sites of Gumara River during our sampling time. In fact, it was very difficult to explain why they were absent in this river, because it has been proven by various studies (Palstra et al ., 2004, Nagelkerke and Sibbing, 1994) that this river is an ideal breeding site for the migratory Labeobarbus species of Lake Tana. From the interviews of some informants (local farmers), juveniles drift to the lake in October, November and December in this river, others said that they observed juvenile fish throughout the dry season. Generally, since we made a very spotty sampling, hence, instead of speculating on the possible attributes depending on the information we have at hand now, detail spatial and temporal data is needed to get pertinent information about juveniles of Labeobarbus drifting in this river. On the other hand, Gelda River, a smaller perennial river and which was not well considered as Gumara River in the study of spawning migration of Labeobarbus migration, yielded a great number of juveniles in our study. A total of 697 juvenile specimens were collected from all the sampling sites of Gelda River. Of this, 576 (82.6%) of the specimens were collected from the river mouth. This indicates that juveniles of Labeobarbus which are hatched in the rivers grow about a mean size of 2.05 cm (Table 2) in the spawning rivers and drift to the lake to feed and grow. However, the higher catch in the river mouth is an indicator that juveniles need to acclimatize themselves to the condition of the lake by spending some time in the lake and river intermediate conditions of the river mouth. Juveniles present in the upstream sites ( ca . 30 km from the mouth) of Gelda River most probably belong to juveniles of the riverine stock of L. intermedius complex . In order to have a clear picture about these juveniles caught in the upstream sites of Gelda, they have to be collected and grown in the aquaria until they reach an identifiable size.
Table 2 : Fish specimens collected in Gumara and Gelda sampling sites
Juveniles of Small Garra L. intermedius Oreochromis Sampling Site Labeobarbus barbs species (adult) niloticus Gelda RM 476 251 3 1 2 Gelda UPI 52 361 ------2 Gelda UPII 18 ------Gelda UPS 151 46 52 1 3 Gumara RM --- 78 ------5 Gumara UPI --- 115 ------Gumara UPII --- 97 ------Gumara UPS --- 18 ------All sites 697 966 55 2 12
Juvenile fish populations are influenced by a variety of biotic and abiotic factors. Examination of potential limiting factors (such as food supply, water quality and habitat suitability) is essential to get a good number of recruits. The total length of juveniles caught in the river ranged from 9 mm to 7.2 mm (both caught in Gelda UPS). Moreover, the mean length (2. 47 cm) of juveniles was highest in Gelda upstream sampling sites (Table 5. 2). This relatively large mean size in Gelda upstream substantiates the assumption that these juveniles can be of the riverine stock of L. intermedius .
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500 450 400 350 300 N of Juveniles 250 200
150
100
50 0 Gelda RM Gelda I Gelda II Gelda UPS
Sampling Site
Fig. 3 : Relative abundance of Labeobarbus juveniles in Gelda River Mouth area ( Gelda Ups; Gelda UPSIII and UPSIV data are lumped).
Table 3 : Average total length of juveniles of Labeobarbus in the different sites of Gelda River
Sampling Site Average Total Length (cm) Gelda RM 2.05 Gelda UPI 2.45 Gelda UPII 2.15 Gelda UPS 2.47 All Sites (Overall mean) 2.14
Fig. 4 . Length class distribution of juveniles in Gelda River, Lake Tana.
In the overall catch, the most frequent size was 1.6 cm, which is the modal value for the histogram of the juvenile fish distribution in Gelda River (Fig. 4). Juvenile size classes below 1.5 cm and above 3.2 cm were caught rarely.
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Table 4 . The density (number of juveniles per square meter) of juvenile Labeobarbus in Gelda River
Sampling Site Density (N/m 2) Gelda RM 2.44 Gelda I 0.29 Gelda II 0.10 Gelda UPS 5.03
In Table 4, we calculated the density of juveniles as a function of beach seine dragged area. And it was higher in Gelda upstream sampling site (Table 5.3). During our sampling we have also visually observed, since the water was clear, mass of juveniles in Gelda upstream sampling sites. The density we have calculated showed sparse distribution of juveniles, but from our observation we can say that juveniles are densely populated in our sampling sites. This low value of juvenile population density may be due to the low catchability coefficient of these juveniles.
Conclusion and recommendation The early life history stages of fishes, from egg to juvenile, have a disproportionately high influence on population dynamics (Gadomski and Barfoot, 1998). Eggs and larvae are more sensitive to environmental effects than older-life stages of fish (Childs, et al ., 1998). From the present and previous spawning migration study results, the reproductive biology of the migratory species of Labeobarbus is summarized in figure 5. The riverine spawners of Labeobarbus species first migrate from the foraging area of the lake to affluent river mouths such as Gelda and Gumara and then migrate upstream in the rivers’ main channels and enter a tributary and spawn. Spent individuals, within a few days return to the lake. The egg will hatch in the tributaries or possibly in the main channels of the river and produce larvae. The larvae during the post rainy season, live in the streams and pockets of large rivers. They do not drift down the river since they can not withstand the torrential river flow. Unlike the spent adult fish, juveniles drift down the main channels of the river very slowly, possibly throughout the post rainy and the dry season. It is well established fact that spawning migration is part of the life cycle of Labeobarbus species of Lake Tana. At least there are some signals that research based management options and regional fisheries legislation are to be in place in the Lake Tana Basin by the Bureau of Agriculture and Rural Development of Amhara Regional State. However, down stream dispersal (drift) of larvae and juvenile fish has received little attention and this missing link need to be clearly investigated in order to maintain recruitment potential. If the larval or juvenile drift is the only form of recruitment into the lake, habitat modification over the rivers that block this route will result in the collapse of this endemic stock.
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Labeobarbus Labeobarbus Labeobarbus Migration to Rivers reach in the sub- Spawn in the sub- tributaries or in the main tributaries or in the main (During the rainy channel spawning sites channel
Labeobarbus Aggregate in the river Labeo- mouths Spent Labeobarbus barbus (Starting at migrate the onset of downstream Larvae rainy in streams and main channel
Labeobarbus Juveniles enter LAKE TANA to the main channel (dry season ) Labeobarbus Juveniles enter into Lake Tana (Before the rainy Labeobarbus Juveniles Feed and season) Grow in the tributary rivers
Fig. 5 . Schematic representation of migratory Labeobarbus spp. Reproduction pattern in Lake Tana
References Balon EK. (1975) Reproductive guilds of fishes: A proposal and definition. J. Fish. Res. Board Can., 32(6):821- 64. Chambers RC, Trippel EA. (1997) Early life history and recruitment in fish populations , Chapman and Hall, London. Childs MR, Clarkson RW, Robinson AT. (1998) Resource use by larval and early juvenile native fishes in the little Colorado River, Grand Canyon, Arizona. Trans. Amer. Fish. Soc . 127: 620-629. Chorowicz J, Collet B, Bonavia FF, Mohr P, Parrot JF, Korme T. (1998) The Tana basin, Ethiopia: intra- plateau uplift, rifting and subsidence. Technophysics , 295:351-67. De Graaf M, Marcel, AM, Machiels M, Tesfaye Wudneh, Sibbing FA. (2004). Declining stocks of Lake Tana’s endemic Barbus species flock (Pisces: Cyprinidae): natural variation or human impact? Biol cons , 116: 277-287. De Graaf M. (2003) Lake Tana’s piscivorous Barbus (Cyprinidae, Ethiopia) Ecology. Evolution. Explitation. PhD thesis, Wageningen Agricultural University, The Netherlands. Eshete D, Vijverberg J, Nagekerke, LAJ, Sibbing FA. (2004) Temporal and spatial distribution of microcrustacean zooplankton in relation to turbidity and other environmental factors in large tropical lake (L. Tana, Ethiopia). Hydrobiologia, 513: 39-49. Gadomski DM, Barfoot CA. (1998) Diel and distributional abundance patterns of fish embryos and larvae in the lower Colombia and Deschutes Rivers. Env. Biol. Fish .51: 353-358. Lamp H, Mohammed Umer, Bates R, Davies S, Eshete Dejen, Coombes p, Marshall M, Zelalem Kubesse, Kebede Seifu. (2004) Discovering the history of the Tana basin, a joint project of the Universities of 179 Ma nagement of shallow water bodies ..., EFASA 2010
Wales, Addis Ababa, and St Andrews, (Scotland), and ARARI. http://www.aber.ac.uk/quaternary/tana/ Mohr PA. (1962) The geology of Ethiopia . University College of Addis Ababa press, Addis Ababa, Ethiopia. Nagekerke LAJ, Sibbing FA. (1996) Reproductive segregation among the large barbs ( Barbus intermedius complex) of Lake Tana, Ethiopia. An example of intralacustrine speciation? J Fish Biol 49: 1244-1266. Nagekerke LAJ, Sibbing FA. (2000) The large barbs (Barbus spp., Cyprinidae, Teleostei) of Lake Tana (Ethiopia), with a description of a new species, Barbus ossensis . Neth J Zool , 2: 179-214. Nagelkerke LAJ. (1997) The barbs of Lake Tana, Ethiopia: morphological diversity and its implications for taxonomy, trophic resource partitioning and fisheries. Thesis, Agricultural University Wageningen,The Netherlands. Palstra A, de Graaf M, Sibbing FA. (2004) Riverine Spawning and reproductive segregation in lacustrine cyprinid species flock, facilitated by homing? Anim Biol , 54(4): 393-415. Swain A. (1997) Ethiopia, the Sudan, and Egypt: The Nile River Dispute. The Journal of Modern African Studies , 35 (4): 675 – 694. Wassie A , Abebe G, Eshete D. (2008) The lacustrine species of Labeobarbus of Lake Tana (Ethiopia) spawning at Megech and Dirma tributary rivers. SINET: Ethiop. J. Sci. , 31 (1): 21- 28.
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Ecological Assessment of Dibanko Bahir Wetland Ecosystem, North-West Amhara Region, Ethiopia
Yezbie Kassa, Bahir Dar University.
ABSTRACT : This study was carried out in Dibanko Bahir wetland, from February 2009 to January 2010, with the objective to identify and quantify the temporal and spatial variation in biodiversity and to analyze the potential socio-economic importance of the wetland. In the dry season the wetland is completely out of surface water and it -3 is used for permanent grazing. Water quality parameters; TDS, EC, DO, pH, PO 4 , NO 3 -N and temperature were measured from three sites (at the inlet, open water and outlet) of the wetland. Temperature, EC, TDS, NO 3–N and -3 PO 4 concentration is higher in the inlet water and during the wet season. But pH and DO are higher in outlet water and wet season. For macrophyte sampling, five sampling sites were stratified based on the vegetation type and area cover; transect and quadrat count technique was employed. A total of 27 plant taxa of 12 families were encountered in these sites. The diversity index (H`) and evenness index (E) were found to be high during post rainy season. Bird species diversity and abundance were measured using count methods, and a total of 36 bird species were recorded. The number of species encountered was different among the four seasons, with the main-rainy season having the highest diversity (H`). Black crown Crane and Cattle Egret accounted for the highest numbers during the dry and wet seasons, respectively. A total of 5,418 macro-invertebrates individuals were collected at the three sites comprising of 7 classes. Chironomidae and Oligochaeta were encountered in all the sites. Oligochaeta was recorded with the highest number at open water site whereas Chironomidae was recorded with the highest number at inlet sites. The diversity (H`) and evenness (E) indices were higher at the outlet site and main-rainy season. Only two types of fish species Labeobarbus intermedius (barbus) and Clarias gariepinus (catfish) with average count of of 13 and 6 per one hour catch effort, respectively, were found in the wetland. The wetland has high socio-economic potential for grazing, irrigation, water supply and ground water recharge. 60 respondents participated in the household survey. From the survey result, fishing was found to be included as an additional alternative for the improvement of the livelihood of local community around the wetland. 80% of the households had 0.1-2.0 size of land holding in the wetland. 100% of the households reported the disadvantage of living around the wetlands due to high incidence of cattle disease, despite the many economic and societal benefits they gained out of the wetland. The expansion of farmlands, settlement and intensive grazing were the main threats to the survival of biodiversities. Lack of full awareness about the value and use of wetlands by decision makers, together with poor public consultation, inadequate stakeholder participation and lack of effective regulation mechanism are all hindering factors for the sustainable use of the Dibanko Bahir wetland.
Key words/phrases: Biodiversity, Dibanko Bahir, important bird areas (IBA), macrophytes, species diversity, species evenness, wetlands.
Introduction Wetland is a collective term used to describe land where an excess of water (that is water lodging) is the dominant factor determining the nature of the soil development and the types of plants and animals living at the soil surface (Breen, 1991). Wetlands support high concentrations of birds (especially waterfowl), mammals, reptiles, amphibians, fish and invertebrate species (Fehringer, 2005). Their function as ecological and hydrological is several fold, for example, flood control, water purification, sediment and nutrient retention, dry season grazing, agriculture, micro-climate, recreation and cultural values, water supply (domestic and livestock), construction (thatching reeds), flood, medicine, as Important Bird Areas (IBA) as well as provision of flyways for migrant birds. But unlike terrestrial ecosystems, the richness of freshwater biodiversity is still poorly known (Ramsar Convention Bureau, 1997, cited in Abebe Yilma and Geheb, 2003). While wetlands may be the most productive of ecosystems on earth, they are also the most threatened (Abebe Yilma and Geheb, 2003). Wetland destruction and alteration has been and is still seen as an advanced mode of development, even at government level. Wetlands and their value remain little understood and their loss is increasingly becoming an environmental disaster (Abebe Yilma and Geheb, 2003). While rates of wetland loss are documented for the developed world, the limited study of these ecosystems in countries like Ethiopia means that a lot has still to be done.
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Wetlands are lost or altered by conversion, over utilization and unregulated management. Deforestation and heavy decline in swamps were observed in connection with change in land use practices including heavy cattle grazing, clearing of the vegetation, construction of dams and irrigation channels and frequent fire as some of the major threats to the Wetland ecosystem. Environmental pollution due to application of agro-chemicals, salinization problem in irrigable lands, overflowing, siltation and soil erosion due to heavy devegetation are the consequences of human impact on this ecosystem. The conversion of swamps to agriculture with long-term drainage and cultivation reduce the diversity of wetland habitats and species. Most of the threats that wetlands face result from their misuse, many are also related to unsustainable resource extraction. Another important reason for their vulnerability is the fact that they are dynamic systems undergoing continual change (Barbier et al., 1996 cited in Abebe Yilma and Geheb, 2003). As a result, many wetlands are temporary features that disappear, reappear and re-create themselves over time. With the basic assumption of wetlands to be less important than any other priorities and due to the increase in population and consequently the lack of agricultural land; wetlands are faced with problem of habitat alteration and most of their animal and plant biodiversity is endangered. In addition, both the quantities of resources available and the biodiversity that comprise these wetlands are little known in formal terms. As a result there are direct anthropogenic activities such as irrational uses of wetlands for agriculture, grazing and withdrawal of water. The protection of wetlands, however, reflects the protection of numerous goods and services that have an economic value not only to the local population living next to wetlands but also to communities outside this wetland area. This study tried to assess the diversity and abundance of flora and fauna, and the major socio-economic benefits as well as the perceptions of local people on the Dibankobahir wetland. It also aimed to analyze the problems facing the wetland ecosystem. Objectives General objective: To assess the diversity and abundance of flora and fauna, and the major socio- economic benefits as well as the perceptions of local people in Dibanko Bahir wetland ecosystem Specific objectives • To characterize the physico-chemical properties of Dibankobahir wetland water; • To identify the diversity and abundance of plants and animals (macroinvertebrates, birds and fish) in the wetland; • To assess and identify the perception of the local people’s social and economic benefits of the wetland; and • To recommend ways that may help in the “wise use” of the wetland.
Materials and methods Description of the study area : Dibanko Bahir is a wetland which is located in Amhara region, surrounded by two kebeles in Dangila woreda: (Girarigie Warkit and Ziguda Gult) and one kebeles (Guta Advy) in Debub Achefer woreda (Fig. 3).
The wetland lies at an altitude of 2039 m with GPS reading of 11 018 ' 0.6 '' N and 036 054 '18.04 '' E .It occupies an area of approximately 75 hectares and is about 4 km long (field observation).
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Gutadvay
Grargie Warkit Dibanko Bahir
Ziguda Gult
7,5003,750 0 7,500 Kilometers
Fig. 3 : Map and location of the study area (Source: ANRS Bureau of Plan and Economy, GIS Team)
There are five villages surrounding the wetland, Abiskan, Dengeshita, Warkit, Woldaficha and Gult, whose livelihoods are supplemented by fish and other wetland products. The wetland habitat has been disturbed through clearing for agriculture, grazing, and foraging activities. Boundaries of the wetland include: River Branti in the North, the main road from Bahir Dar to Dangila in the south, Gult Kebele in the east and Abishikan and Ziguda Kebele in the west (Fig.4).
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7,5003,750 0 7,500 Kilometers Legend: Fig.4 : Dibanko Bahir and its boundaries Boundaries of Dibanko (Source: Ethiopian Mapping Agency).
Climate : According to the Ethiopian agro-ecological zonation, the wetland and its surrounding areas lie in Woyna Dega zone (warm to cool) and the mean annual temperature of 18.8 oC (maximum 20 oC and minimum 17.5 0C) seasonal variations mainly four, winter (rainy season), summer (dry season) autumn (small rain) and spring (a spell between long rain and dry seasons). The climate of Dibanko Bahir is characterised roughly by four seasons: (1) A main-rainy season with heavy rains during July– September, (2) A dry season during December–April, (3) A pre-rainy season during May–June and (4) A post-rainy season during October–November Hydrology : The wetland is seasonal type with varying size and water levels at different seasons. It is predominantly fed by ground water and/or spring flow, as well as surface flow during the wet season.The wetland has standing water depth of between 1.35meter in the main rainy season and up to1 meter in the pre-rainy and post-rainy seasons. The shallow part have soils that are saturated to inundation by standing water up to 1.35 meter in depth, throughout most of the growing season. It becomes completely out of surface water at least for two-three dry months.There is a great seasonal water level fluctuation. The mean annual rainfall is 1650mm, ranging from maximum of 1800mm to a minimum of 1500mm. On average 80% of the total annual rainfall occurs between June to September with the highest mean recorded in July (1800mm) and the minimum rainfall is 1500mm during autumn. Soil Type : The type of soil has strong correlation with physiography, geology and climate of the area.the major soil types of the study area are Chromic Luvisols (CL) and ChromicVertisols (CV) (Fig.6).
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Lc Lc 7,5003,750 0 7,500 Kilometers
Vc Vc
Legend: Major soil types of the study area Chromic Luvisols (LC) ChromicVertisols (VC)
Fig.5 : Soil type of the project area Source: ANRS Bureau of Plan and economy (GIS Team)
Such soil types are black and poor water drainage capecity. It is highly compacted especially during the dry season. There are sparsely distributed trees and shrubs like vegetation in the shore area such as Carissa edulis (Agam), Euphobiaceae (Bisana), Acacia lahae (Tikur girar), Vernonia amygdalina (Girawa), Cordia africana (Wanza), Ficus species (Shola), Eucalyptus camaldulensis (Barzaf), etc. Plate.1 in appendex III shows photograph of some of these species. Farmers live near the wetland had livelihood directly linked to the wetland as they benefit from the wetland in several ways: For instance, a large majority of them were engaged in livestock grazing, others were engaged in small scale irrigation using water from the wetland and some others were engaged in fishing activity mainly in the rainy season, even using their clothes (plate. 2) and some are found engaged in daily collection of Scirpus validus from the wetland for the construction of local reed raincoat (in amharic Gessa). Apart from the economic benefit from the wetlands, they also used water from the wetlands for sanitation purposes and for household purposes, except drinking. All of the cattle horses and other animals are entirely dependant on the wetlands for drinking, in addition to grazing. Sampling methods: This study was carried out for a year (from February 2009 to January 2010) at the selected sites on seasonal basis (dry, pre-rainy, main-rain and post-rainy seasons) to determine the temporal and spatial variation of biodiversity in the wetland. Field surveys were carried out in the wetland to collect data on types and conditions of water quality, flora, fauna and land use of the area. The sampling sites for water quality parameter and macro-bentic invertebrate assessment was selected based on the assumption that there will be variation in the water quality nature at the inlet, open water and outlet where as for macrophyte sampling and bird species data collection, five major vegetation zones (communities) were identified (the Grassland dominated, Hygrophila auriculata dominated, Cyperus dominated, Cyperus and rush mixed dominated and Rush dominated). Figure 5 shows the location of sampling sites fpr water quality parameters, bentic community, macrophyte (vegetation) community zones and bird species in the study area.
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7,5003,750 0 7,500 Kilometers
Fig. 6 . Map showing the location of sampling sites in the study area
Water Quality Analysis : The following methods were used in measurement and analysis for water quality determination of the study wetland: • pH and temperature were measured with coupled pH/mV/O meter(Model CE370 pH meter 01186,EU). • Electrical conductivity was measured with cond/TDS meter (Model CE 470 Cond Meter 01189) • Dissolved oxygen with oxygen meter (OXi 31 5i, WTW82362). • Secchi transparency readings was done with a Secchi disc • Water samples were collected from each site and analyzed for Phosphate and nitrate concentration. Analysis of nitrate and phosphate samples were done immediately after collection with a mobile water analyses kit (Wagtech international, Palintest transmittance display photometer 5000, Palintest Ltd., UK) in fisheries and aquatic science research institute laboratory. Water samples were filtered through a 0.45 µm mesh membrane filter before analyses. The nitrate and phosphate concentration of the water was determined photo electrically using the Palintest photometer. In order to separate the effect of turbidity, color of the samples were compared against filtered portion of the same water i.e. the filtered water sample was used as a blank for each site. Nitrate was determine by the palintest-nitratest method and phosphate was determined by palintest-phosphatler method. Samples of expected high concentrations of the respective chemicals were diluted so that they could be measured within the linear detectable range. 186 Ma nagement of shallow water bodies ..., EFASA 2010
• All field measurements were taken by dipping the probe about 3-5cm below the water surface. Flora Assessment : During the reconnaissance survey, five major significant vegetation zones (communities) were identified (the Grassland dominated, Hygrophila auriculata dominated, Cyperus dominated, Cyperus and rush mixed dominated and Rush dominated). Quadrat sampling method was employed to identify vegetation in each vegetation zone (Daracon Quarries, 2007). Macrophyte community was analysed by stratified random sampling using 1m x 1m height wooden quadrat. The number of quadrats within each sampling unit was adjusted according to the length of the community. The macrophytes were counted by hand picking. One quadrate from each community (sampling units); altogether 5 quadrates in the wetland were studied in each season-. The plant species were identified with the help of standard literature (Edwards, 1976 and Fichtl and Adi Admasu, 1994) as identification key. Identification was also assisted by camera photography. Plant biomass estimation • Of macrophyte samples in each quadrate 1/4 th of the total number of the samples were taken and returned to the the chemistry department analytical laboratory and separated by species. • To achieve constant weight per unit volume of plant biomass, the sample plants were first dried at 105 oc for 24 hours in oven • The weights of plants were measured at intervals of 10 minutes until constant mass was obtained after ensuring complete drying. The final mass measured was reported as dry weight of the sample plants/m 2 • Samples were incinerated at 1000 0c for 1hour to obtain the biomass of the plants. Bird diversity : Field binoculars were used for bird observation and theyidentified by the use of dichotomous keys and commercially available field guides (Terry and John, 2004). • Plot counts a minimum of 20 minute search within a 1.0 ha area (100 m x 100 m, 50 m x 200 m, etc.) was applied. • Data collection was carried out for 5 h a day from 6:30-10:00 a.m. in the morning and from 4:30 to 6:00 p.m. in the afternoon, when the activities of birds were prominent. • The perpendicular distance from which the bird occurred to the transect line was estimated and then the type and the group number of species were recorded using direct observation. • The counted and recorded individuals were identified. Identification was assisted by binoculars. Benthic macro invertebrates: Benthic macro invertebrates were collected using Ekmann grab sampler at three sampling sites. • Samples were poured through a 500 µm sieve and invertebrates retained on the sieve were preserved in 95% ethanol and returned to the laboratory for further identification and enumeration. • Each macro-invertebrate (size > 500 µm) specimen was identified to the lowest taxon using the keys in Merrit and Coommans ( 1996). Each sample was hand sorted from the substrate and identified to the lowest possible taxa using a light table and stereo dissecting microscope. Counting was done using a gridded glass counting chamber (rafter cell) with 24 grids, at the Fisheries and Aqutic Science Reaserch Institute laboratory. Macro-invertebrate identification was done only at family level. Socio-economic survey : The Land use patterns and activities of people around the wetland were assessed and mapped using Geographical information system (GIS). • The GPS reading was first recorded using the instrument GPS. • The recorded data were processed in Arc map and Arc View GIS soft wares. The following data sets were used to generate the field map for use: • Google Earth satellite image(2008) with woreda andand kebele boundary • Woreda andand Kebele shape files of Amhara National Regional State- from ANRS, plan and economy Bureau, Department of GIS • Wetlands of ANRS from Department of Environment and Climate Change website download • ATLAS of West Gojjam andand Awi Zone- from ANRS, Plan and Economy Bureau, Department of GIS • Land use mapping for ANRS-from ANRS, Plan and Economy Bureau, Department of GIS 187 Ma nagement of shallow water bodies ..., EFASA 2010
Where required data sets were converted to the new datum (GDA 1994) using geographic coordinates (latitude – longitude, represented on maps in degrees, minutes and seconds). Socio economic data: Structured questionnaires were used to collect socio-economic data (Appendix 1) from the local communities, and oral interviews were conducted with the beneficiaries at various levels to explore the economic and societal benefits of the wetlands under investigation. Of the total households from the local communities in the surrounding wetlands (591), about 10% (60) households were selected to respond to the questionnaires. Collecting data through questionnaires and oral interviews were carried out in October 2002 by three enumerators, all of whom were awared on how to collect relevant information during the interviews. The main criteria for respondent selection were based on at least one year of residency around the wetlands. Data Analysis and Computations: GPS reading along the perimeters of the wetland was used to delineate and map its coverage. Topographic maps of similar scale (1:50 000) as well GPS reading from ground surveys was processed by ARC GIS 9.1 to produce land use map. The spatial and temporal variations of physico-chemical parameters were analized using one way analysis of variance and floral and faunaa diversity indices were analyzed using non parametric chi-square test. The Shannon-Wienner Index (1949) was used to calculate Richness, Diversity and Evenness of each species.
H`= -Σ pi log e pi, E = H`/H max =H`/log s and D=S/ √N i=1
Where: E = evenness Hmax = the maximum diversity of a sample H` = the value of Shannon-Winner diversity index Pi = the proportion of the ith species Log e = the natural logarithm of pi S= the number of species in the community N=total Number of organisms in each species Quantitative and qualitative social scientific methods and descriptive statistics were used to summarize the primary data collected through questionnaires. The analysis covered frequency counts, percentages average (mean) and ranges. In general, the Statistical Package for Social Science (SPSS) version 12 ms-excel was employed to analyze data from both primary and secondary sources.
Result Water quality: During the dry season the wetland was completely out of surface water so that it was imposible to discuss about the water quality in this season. Tables 4 and 5 show the data collected during the three seasons (pre-rainy, main rainy and post rainy seasons) and the three sites (inlet, open water and outlet sites).
Table.4 : Means and standard errors of water physico-chemical parameters in the three seasons, namely, pre-rainy, main-rainy and post-rainy. (Temp.: Surface water temperature, DO: dissolved oxygen, Cond.: conductivity, TDS: total dissolved solids, min: minimum, max: maximum, SE; standared error).
Sampling Statistical Parameters tools season pH DO Temp Cond TDS Secchi NO 3-N PO 4 (mgl -1) (0c) (µµµscm -1) (mgl -1) (cm) (mgl -1) (mgl -1) mean 5.96 5.37 25.53 80.67 35.7 23.33 3.07 0.37 Pre- min rainy 5.09 5.2 22.6 71.6 21 11 1.95 0.19 period max 6.61 5.5 27 97.9 48.1 38 1.95 0.59 SE 0.78 0.15 2.54 14.93 13.70 13.65 0.38 0.21 mean 7.27 5.83 26.6 86.97 89.23 9.33 3.67 0.60 min 7.1 5.2 25 77.6 78.2 6 2.7 0.19
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Sampling Statistical Parameters tools season pH DO Temp Cond TDS Secchi NO 3-N PO 4 (mgl -1) (0c) (µµµscm -1) (mgl -1) (cm) (mgl -1) (mgl -1) Main- max 27.8 96.7 98 13 5.2 1.28 rainy 7.5 6.2 period SE 0.21 0.55 1.44 9.56 10.09 3.51 1.34 0.59 mean 5.33 6.1 20.73 50 40.23 31.43 2.22 0.84
min Post- 4.7 5.8 20.6 30 35.8 10.3 1.34 0.45 rainy max 21 80 48.1 53 3.4 1.2 period 5.7 6.4 SE 0.55 0.3 0.23 26.46 6.83 21.35 1.06 0.38
The mean pH values showed variation across all the sampling sites and sampling seasons. The values at each study site sample plots fall with the range between 7.5 and 4.7 log units (mean 6.1 log units). The maximum pH value (7.5 log units) was observed in main- rainy season in outlet site whereas the minimum pH value (4.7 log units) was recorded during the post-rainy season in the open water site. The pH values in all of the three sampling sites and sampling seasons deviated from the neutral pH value towards an acidic medium (pH<7). The mean dissolved oxygen concentration varied only within a narrow range (5.37-6.1mgl -1, mean=5.7mgl -1). The seasonal values were 5.37, 5.83 and 6.1 mgl -1 in the pre-rainy, main rainy and post rainy season, respectively (Tables 4 and 5), whereas the spatial values was 5.4, 5.93 and 5.97 mgl -1 in the inlet water, open water and in the outlet site respectively. The mean surface water temprature was high (26.6 0c) during the main rainy season in the inlet site and low (20.73 0c) during the post rainy season in the open water site (Tables 4 and 5). The mean conductivity was 80.67, 86.97 and 50 µscm -1 in pre-rainy, post-rainy and main-rainy season, respectively (Table 5). The highest value was recorded during the main –rainy season in the inlet site and the lowest value recorded during the post-rainy season in the outlet site.
Table.5 : Means and standard errors of water physico-chemical parameters in the three sites, namely, inlet, open water and outlet. (Temp.: surface water temperature, DO: dissolved oxygen, Cond.: conductivity, TDS: total dissolved solids, min: minimum, max: maximum, SE: standared error). Parameters Sampling Statistcal pH DO Temp Cond TDS Secchi NO 3-N PO 4 site tools (mgl -1) (0c) (µµµscm -1) (mgl -1) (cm) (mgl -1) (mgl -1) mean 5.96 5.4 25.27 91.53 64.73 10.1 4.3 1.02
min 5.09 5.2 21 80 48.1 9 3.4 0.59 max inlet 7.1 5.8 27.8 97.9 98 11 5.2 1.28 SE 1.03 0.35 3.72 10.00 28.81 1.01 0.9 0.37 mean 6.17 5.93 22.73 63.07 50.9 34.67 2.52 0.47
min Open 4.7 5.5 20.6 40 35.8 13 1.91 0.19 water max 7.2 6.2 25 77.6 78.2 53 2.95 0.88 SE 1.30 0.38 2.20 20.20 23.69 20.21 0.54 0.36 mean 6.43 5.97 24.87 63.03 57.13 19.33 2.13 0.32
min outlet 5.6 5.4 20.6 30 36.8 6 1.34 0.19 max 7.5 6.4 27 86.6 91.5 31 3.1 0.45 SE 0.97 0.51 3.70 29.46 29.93 12.58 0.89 0.13
As shown in Table 4, the seasonal variation of total dissolved solids ranged from 35.7- 89.23 mgl -1. The recorded mean TDS values in the three sampling sites were 64.73, 50.9 and 57.13 mgl -1 in the inlet, open water and in the outlet sites, respectively. The minimum mean value was recorded during 189 Ma nagement of shallow water bodies ..., EFASA 2010 the pre-rainy season in the open water site and the maximum value was recorded during the main- rainy season in the inlet site. The nitrate concentrations in each sitehad mean values of 4.3, 2.52 and 2.13 mgl -1 in the inlet, open water and in the outlet sites, respectively (Table 5). The mean nitrate concentration also showed variation among seasons (3.07, 3.27 and 2.22mgl -1in the pre-rainy, main rainy and post rainy seasons, respectively) (Table 4). Table 4 shows the recorded seasonal mean soluble reactive phosphate (PO4 –3) concentration. The data collected was 0.37, 0.6 and 0.84 mgl -1 in the pre-rainy, main rainy and post rainy seasons, respectively. The mean Phosphate concentration also showed variation among sampling sites (1.03, 0.47 and 0.32 mgl -1 in the inlet water, open water and outlet sites, respectively. Statistical analysis, using one way ANOVA test showed that there was no significance difference in all the parameters among the three sites (p > 0.05) but there was significant difference in mean value of temperature(p = 0.012), pH (p = 0.015 ) between main-rainy and post-rainyseasons and TDS (p = 0.001) between main-rainy and pre-rainy seasons. Vegetation : A total of 27 macrophyte species grouped in 12 families recorded during the study period (Tables 6 and 10). During the dry and pre-rainy seasons, 11 macrophyte species containing an average of 843 and 823 individuals per meter square were recorded, respectively, whereas during the main-rainy season 13 species containing 1095 average number of individuals per square meter were recorded. The numbers of species recorded during the post-rainy season were 27 and the average numbers of individuals were 1928m -2. The relative percentage of abundance of macrophytes in dry, pre-rainy, main- rainy and post-rainy seasons are shown in Figure 7. In all the seasons Polygonum setulosum was the dominant species in that it accounted for 50% in pre-rainy, 54% in main-rainy, 33% post-rainy and 68% in dry seasons of the total macrophyte abundance. . The number of taxa in the four seasons was subjected to diversity and evenness analysis and the result is presented in Table 7. The index value, H` ranges from 0.432 to 1.08 and evenness E, from 0.432 to 0.77. The highest diversity index value (1.08) and eveness value (0.77) was recorded during the post- rainy season and the least diversity index and eveness value (0.432) was during the dry season. Though there is a minor difference according to the non parametric chi-square test, there is no significant difference in diversity and evenness indiecs among seasons. The spatial variation in diversity and evenness index of macrophytes were also analyzed and the result is presented in Table 8. The range was from 0 to 1.98. Zero diversity and evenness indices show the presence of only one species in the area. The highest value was observed in the Rush dominated community during the post rainy season. The seasonal macrophyte (plant) biomass at each community is shown in Table 9. The highest biomass (18.84gmm -2) was measured during the post rainy season and the least biomass (2.74gmm -2) was measured during dry season. As indicated in Table 9, Scirpus validus had the highest biomass during the pre-rainy season, next to Juncus effuses . In this season the least biomass was recorded for Hygrophila auriculata (0.62gm). During main rainy season next to Juncus effuses, Commelina diffusa species had the highest biomass.The least biomass was of scirpus validus . In the post rainy season next to Juncus effuses,e Commelina diffusa hasthe highest biomass and the least biomass is observed for Scirpus validus . During the dry season, the least biomass was observed for Polygonum setulosum
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Table 6 . Seasonal distribution of macrophytes in Dibankobahir wetland.
seasons Pre- Main- Post- Familly Scientific name dry rainy rainy rainy N=4114 N=5473 N=9640 N=4213 Crinum 0.2 0.1 0.02 0 Amaryllidaceae abyssinicum Bidens macroptera 0 0 1 0 Sonchus asper 0 0.3 0.2 0.2 Sphaeranthus 0 9 2 0 Asteraceae suaveolens Gynaphalium 0 0 0.7 0 rubriflorum Commelina 0 0 8 0 Commelinaceae benghalensis Commelina diffusa 8 10 5 2.5 Aesschynomene 12 12 7 0 Leguminosae abyssinica Trifolium acaule 0 0 8 0 Plectranthus 0 0 0.05 0 Limiaceae puctatus Lemna 10 0 0.5 0.3 Perisicaria 0 0.1 0.1 0.1 Polygonaceae setosula Hygrophila 1 1 1 0.6 Acanthaceae auriculata Scirpus validus 5.6 5 3 0 Cyperaceae Scirpus cyperinus 0 0 0.5 0 cyperus bipartitus 0 0 3 0.1 Juncus 0 0 3 0 roemerianus Scheele Rhynchospora 0 0 4 0 Juncaceae macrostachia Schoenoplectanus 0 0 5 0 pengens Juncus effusus 5 8 5 15 Scheoplectusa 0 0 3 0 acutus Nymphaceae Nelumbo lutea 0 0 2 0.3 Polygonum 50 54 33 68 setulosum Apiaceae Hydrocotyle 0 0.3 0.8 0 umbellate Poacea phragmites 0.1 0.1 0.2 0 australis Total 100% 100% 100% 100%
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12000 9640 10000
8000 5473 6000 4213 4114 4000 2000
total no total of induviduals 0
Dry Pre-rainy Wet/rainy Post-rainy
Fig.7 . Comparison of total number of macropytes in the four seasons
Table.7 : Macrophyte diversity index and evenness index in the four seasons
Seasons (periods) H` E Dry 0.432 0.432 Pre-rainy 0.668 0.668 Wet/rainy 0.563 0.526 Post-rainy 1.08 0.77
Table 8 : Macrophyte diversity at the five quadrates (Communities) in the respective seasons
Quadrates Dry Pre-rainy Main-rainy Post-rainy H` E H` E H` E H` E 1 0 0 0.39 0.56 0.4 0.57 0.51 0.51 2 0 0 0.59 0.76 0.66 0.85 1.88 1.98 3 0.24 0.39 0.52 0.744 0.48 0.68 1.60 1.36 4 0.65 0.835 0.42 0.49 1.28 2.13 1.00 0.78 5 0.28 0.93 0 0 0.33 0.69 0 0
Table 9: Biomass values of the macrophyte (gm.m-2) in the four seasons
Pre-rainy Main-rainy Post-rainy dry Plant species season season season season Polygonum setulosum 0.8 0.30 2.28 0.11 Aeschynomene abyssinica 1.84 1.75 1.68 0 Potomegton 1.09 2.24 2.31 0.51 Scirpus validus 2.36 0.16 0.88 0 Hygrophila auriculata 0.62 0.20 1.33 0 Juncus effuses 2.48 7.60 7.75 2.12 Juncus roemerianus Scheele 0 0 1.13 0 Rhynchospora macrostachia 0 0 1.96 0 Trifolium acaule 0 0 1.28 0 Total 9.19 12.25 18.84 2.74
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Table.10 . List of macrophytes identified from Dibankobahir wetland
Seasons (period) Familly Scientific name Pre- Main- Post- dry rainy rainy rainy Amaryllidaceae Crinum √ √ √ x abyssinicum Bidens macroptera X x √ x Sonchus asper X √ √ √ Sphaeranthus X √ √ x Asteraceae suaveolens Gynaphalium X x √ x rubriflorum Commelina X x √ x Commelinaceae benghalensis Commelina diffusa √ √ √ √ Aesschynomene √ √ √ x Leguminosae abyssinica Trifolium acaule X x √ x Plectranthus X x √ x Limiaceae puctatus Lemna √ x √ √ Polygonaceae Perisicaria X √ √ √ setosula Acanthaceae Hygrophila √ √ √ √ auriculata Scirpus validus √ √ √ x Cyperaceae Scirpus cyperinus X x √ x cyperus bipartitus X x √ √ Juncus X x √ √ roemerianus Scheele Rhynchospora X x √ x Juncaceae macrostachia Schoenoplectus X x √ √ pungens Juncus effuses √ √ √ √ Scheoplectusa X x √ x acutus Nymphaceae Nelumbo lutea X x √ x Polygonum √ √ √ √ setulosum Apiaceae Hydrocotyle X √ √ x umbellate phragmites √ √ √ x australis poecea Echinochloa √ √ √ √ crusgalli (L.) Beauv
Fauna Communities Bird Survey : A total of 36 bird species was recorded during the study period (Table 11).
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Table 11 : List of birds identified in Dibankobar Wetlands during dry, pre-rainy, rainy and post-rainy seasons
Pre- Main- Post- Familly Scientific names Common names Dry rainy Rainy ainy season season season Gruidae Balearica Black Crowned Crain pavonina Threskiornithi Bostrychia dae carunculata Wattled Ibis Ardeidae Bubulcus ibis Cattle egret Anatidae Plectropterus Spur-winged goose gambensis Anatidae Alopochen Egyptian Goose aegyptiacus Threskiornithi Threskiornis Sacred Ibis dae aethiopica Threskiornithi Plegadis Glossy Ibis dae falcinellus Threskiornithi Bostrychia Hadada Ibis dae bagedash Ardeidae Ardea Black headed grey melanocephala heron Rallidae Fulica cristata Red-knobbed coot x x x Anatidae Thalasorrnis White-backed Duck x leuconotus Scolopacidae Actitis hypoleucos Common sand piper x Rostratulidae Dromas ardeola Crab plover x
Charadriidae Charadrius White fronted plover x x arginatus Scolopacidae Gallinago Common Snipe x gallinago Charadriidae Black winged Plover x Anatidae Anas undulate Yellow billed duck x Ciconidae Ciconia ciconia White stork x Burhindae Burhinus Spotted thick-knee x x capenisis Ciconidae Anastomus African open billed x x lamelligerus stork Ciconidae Ephippiorhynchus Shaddle billed stork x x x senegalenss Ciconidae Mycteria ibis Yellow billed stork x x Scopidae Scopus umbretta Hammer kop x x Anhingidae Anbinga rufa African darter x x x Jacanidae Actophilornis African Jacana x Africana Ciconidae Leptoptilos Marabou stork x x crumeniferus Ardeidae Ardea cinerea Grey heron x Ardeidae Ardea goliath Golith heron x x x Anatidae Anas sparsa African Black Duck x x Scolopacidae Tringa stagnatilis Marsh sandpiper x x Charadriidae Vanellus African wattled x x x senegallus lapwing Phalacrocora Phalacrocorax Long tailed cormorant x x x cidae africanus 194 Ma nagement of shallow water bodies ..., EFASA 2010
Pre- Main- Post- Familly Scientific names Common names Dry rainy Rainy ainy season season season Glareolidae Rhinoptilus Two-banded courser x x x africanus Charadriidae Vanellus spinosus Spur-winged lapwing x x x
Scolopacidae Stone curlew x
Table 12 : Abundance of bird species commonly found during the four seasons
Seasons Common name Pre-rainy Main-rainy Post-rainy dry Black crowned crain 18 23 36 223 Wattled ibis 36 38 45 25 Cattle egret 316 350 263 22 Spur-winged geese 27 23 26 7 Egyptian geese 26 44 35 8 Sacred ibis 90 102 163 21 Glossy ibis 82 98 98 23 Hadada ibis 107 110 109 24
The number of taxa in the four seasons was subjected to diversity and evenness analysis and the result is presented in Table 13. From the table one can observe the diversity index, H` ranged from 0.704 to 1.659 and E ranged from 0.614 to 1.146. According to the non parametric test chi-square test, there is no significant difference in diversity and evenness indices among seasons.
Table 13: Diversity Index of Birds during the four seasons
Diversity index Evenness index Seasons (H´) (E)=H`/logS Pre-rainy 1.093 0.78 Wet 1.659 1.146 Post rainy 1.045 0.74 Dry 0.704 0.614
The relative composition of bird species commonly found in the four seasons (pre-rainy, main-rainy, post-rainy and dry seasons) is shown in Figure 8.
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400 350 Pre-rainy 300 250 200 Main-rainy 150 100 Post-rainy 50 0 t dry in is se is is ra Ib gre o Ib Ib d e d a d C le go e tt tle d cre ad ian Goose Sa Glossy Ibis own Wa Cat Had ur-wingeEgypt ck Cr p la S B Fig. 8 . Relative composition of Bird species commonly found during the four seasons
Macro-invertebrates communities: Macroinvertebrates of 7 classes, representing 11orders, 15 families were identified in the wetland (Table 14).
Table 14 : List of Benthic Macro-Invertebrate Taxa Identified in Dibankobar Wetlands.
Seasons Class Order Family Pre- Main- Post- Open Outlet Inlet rainy Rainy rainy water Oligocheata Oligocheata Naldidae Bdelloidae x x x Hirudinae Hirudinea leeches x x Psephonidae x x x x Coleoptera Elmidae x Simulidae x x x x Diptera Chironomidae Tricoptera Hydropsychid x x x x Insecta ae Hemiptera Water bugs x x x Odonata Dragon fly x x x x nymph Arachinida Acariforms Water spider x x x x Gastropideae x Gastropoda Ploima Branchiopoda Cladocera Moinidae x x x x Nematoda Nematoda Nematodes x
Seven taxa were collected only once and five taxa were common to all sampling seasons. Ten taxa were identified in only one sampling site whereas three taxa were common to the three sites (Table 15).
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The abundance of the seven Classes of bentic macro- invertebrates recorded from the three sites are shown in Table.16 and the Oligocheata were the most abundant in the open water and outlet sites(47.01% and 59.8% respectively) whereas insects were abundant in the inlet site (79.82%).
Table.15 : Abundance of the seven classes of bentic macro-invertebrates recorded from the three sites
Inlet Open water Outlet Class Total No. Abundnce Total No. Abundnce Total No. Abundnce Oligocheata 222 9.18 2597 47.01 888 59.8 Hirudinae 0 0 243 4.4 0 0 Insecta 1930 79.82 2552 46.2 465 31.31 Arachinida 44 1.82 0 0 44 2.96 Gastropoda 222 9.18 44 0.8 44 2.96 Branchiopoda 0 0 44 0.8 0 0 Nematoda 0 0 44 0.8 44 2.96 Total 2418 100% 5524 100% 1485 100%
Table16 : Abundance of the seven classes recorded for the three seasons
Seasons Class Pre-rainy Main-rainy Post-rainy Oligocheata 40.82 46.62 1.02 Hirudinae 2.61 3.07 0.68 Insecta 51.34 40.06 95.25 Arachnida 0 0.68 0 Gastropoda 2.61 4.79 8.86 Brachiopoda 0 4.11 0 Nematoda 2.61 1.36 2.38 Total 1683 6478 6501
The number of taxa in the sites was subjected to diversity and evenness analysis and the result is presented in Table 17. Diversity index, H` was highest at outlet site (0.424) with slight difference from openwater site (0.4197) and lowest at inlet site (0.299). Although inlet site is the least diverse, its evenness is comparable with open water site.
Table 17. Diversity index of benthic macro- invertebrates among sampling sites
Sites Total Diversity Evenness(E) No. index (H`) Inlet 2418 0.299 0.4967 Open 5524 0.4197 0.537 Outlet 1485 0.424 0.61
When species composition was compared among the three seasons, the index value, H` ranged from 0 to 0. 661 and evenness E, ranged from 0 to 0.577 (Table 18). According to the non parametric chi- square test, there was no significant difference in diversity and evenness indices among seasons.
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Table 18 . Diversity Index of Benthic Macro- Invertebrates among Seasons
Total diversity index Season Evenness(E) No (H`) Pre-rainy 1683 0.411 0.486 Main-rainy 6256 0.661 0.577 Post- rainy 6190 0.175 0.194 Dry - - -
Socio-economic Data: Though the wetland is surrounded by three kebeles most area of the wetland is mainly surrounded by Gult and Abishikan kebele. This kebele has 5 villages these are Mehal Abishikan, Tumhoch, Wusafiwech, Dangiloch and Cheboch. There are a total of 591 households in the kebele. Among these, 526 were males and 65 were females. The 60 household’s survey had a total population of 300, which translates to an average family size of 5.01 people. However, it ranged from 2 to 10. The large majority of the people living in the periphery of Dibanko Bahir wetland are quite young in age like in many areas of the rural parts of Ethiopia. The age structure of the respondents shows that the majority of the heads of households (54.97%) fall in the actively working age group between 20 and 45 years old, 32.19% were younger participants and 19.29% were at the age of >45. Interms of education, it was found that nearly 53.33% of the interviewed heads of households had no schooling, of which 41.67% of the heads of house holds were illiterate, and the rest 11.3 % could only read and write. 38.33% of the interviewed heads of house holds had primary education while 14.29% had access to secondary education. When interviewed for how long years they have been in their respective wetland areas, the majority of the heads of households (nearly 38.3329%) answered about 6 to 10 years. Generally, more than 80% of the heads of the households who were covered by the questionnaire survey were living for more than 6 years. According to their response, nearly half of the households are local, in the sense that the heads of households were born in the areas concerned. Land use/cover (LULC) pattern: Table 19 indicates the land use/cover pattern of the wetland and its adjacent area. Out of the total area coverage 80% was coverd by Grass land, 12.5% by sedentary cultivated land, 4.5% by natural forest and 3% by planted forests. This indicates that the total area coverd by forests was only (7.5%) as compared to the grassland coverage (80%).
Table 19 : Land use land cover (LULC) pattern of the wetland and its adjacent area Source : ANRS Bureau of Plan and economy (GIS Team)
Land use Area Status Characteristics type cover (%) GB 48.8 With few stocks of woody plants Grass land GB/HSS 31.2 With few stocks of woody plants Grass land CRCM 14.5 With moderate stocks of woody plants Sedentary cultivated FRO 2.5 Open forest cover Natural forest FPO 3 Open forest cover Planted forest
Major crop types that are produced around the wetland are like: teff, maize, barely, wheat, and bean, finger millet, and Niger seed. In the wetland of Dibanko Bahir, the stakeholders include: • Women water collectors who use wetlands on a daily basis • Men who engaged in wetland farming, both those who farm for themselves as well as those who are share croppers or are paid labourers, • Cattle owners who graze their animals in wetlands, • Upslope farmers who affect wetlands by what they do on their land, and can be affected by changes in wetland water tables if they have land near the wetland edge,
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Table 20 : Land size and household holding by land category
Size of land Perennial Perimanent Land size Forest land holding in the crop land cropland wetland 0 3 (5%) 28 (46.67%0 49 (81.67%) 11 (18.33%) 0.1-0.5 19 (31.67%) 13 (21.67%) 6 (10%) 21 (35%) 0.5-1.0 25 (41.67%) 17 (28.33%) 5 (8.33%) 12 (20%) 1.0-2.0 13 (21.67%) 2 (3.33%) 0 16 (26.67%) Total 60 (100%) 60 (100%) 60 (100%) 60 (100%)
As can be observed from Table 20, the majority of the heads of households (41.67%) have perennial cropland with holding size between 0.5 and 0.1 ha, and 5% do not have perennial croplands. With regard to the permanent cropland holding, the majority of households (46.67%) do not have land in its category. However, 21.67% of households have permanent cropland with holding size between 0.1 and 0.5 and 3.33 % of the households have permanent croplands having 1.0-2.0 ha of land size. The majority of households that do not have land among the stated land categories belong to the forest land (81.67 %). When compared the size of landholding in the wetlands, 35%, 20% and 18.33% of households accounted for holding size between 0.1 and 0.5 ha, 1.0 and 2.0 ha and 0.5 and 1.0 ha respectively. Farming is not the single most important source of income for the households concerned. It was found that around 92% of the respondents have their own secondary occupation in one way or another. Most of them are engaged in livestock rearing and daily labors. From the survey conducted, none of the households was found being engaged in a single occupation for their primary source of income. With regard to livestock ownership, the result revealed that 89.93 % of households had livestocks of different type but the number in a household ranges from 0 (have no livestock) to eight and When asked how frequently they took the livestock to the surrounding wetlands for grazing, 100% of the households reported that they take them every day. The evidences of this study suggested that the wetland serve the needs of the people in one-way or other at various levels (individuals, family, community, and village). This is because the overwhelming majority of the households (97.37%) covered by the questionnaire survey stated that they had livelihood directly linked to the Dibanko Bahir wetland. Of the 97.37% of households it was found that 91% of the respondents are engaged in raring of animals grazed on the wetland.50% of the respondents were engaged in cultivation of crops/ vegetables/fruits using water from the wetland, However, 34.25% was found engaged in daily collection of cirpus validus from the wetland for the construction of local rain coat (in amharic Gessa) and 36.76% were engaged in fishing activity mainly in the previos years. Apart from the economic benefit from the wetlands, 53(88.33%) of the households reported that they used water from the wetlands for sanitation purposes and 42 (70%) used for household purposes except drinking. Furthermore, when asked how close they live from the wetlands concerned, 100% of the households surveyed answered that they are living very close (with in 30 minutes walk) from the wetlands. When asked whether or not there are disadvantages of living around the wetlands, 100% of the households reported that there are disadvantages, of which according to their responses, 88.33% of the respondents replied that the area was highly susceptible to cattle disease locally known as ` `Gubet Beshita’’ , which means to say liver disease. Leach attack is also another disease that affects their cattles. According to the responses of 30% of the households the area was highly exposed to crop damages as well by wild animal attacks such as birds of different species like Spur-winged geese, Crane and Egyptean geese. And also 11.67% of the respondents reported that their farmlands were affected by rising water level during the rainy season (mainly in July and august). Besides the stated disadvantages, the households also mentioned that bad smell of wetland in rainy season and Bilharzia disease ( Schistsoma ) whose hosts were detected in macroinvertebrate sampling in the areas were among the major disadvantages. 199 Ma nagement of shallow water bodies ..., EFASA 2010
The study revealed that the wetland had main values as shown in the table below. The table shows the wetland`s main values with their level of significance.
Table 21 : The main values of the wetlands and their level of significance.
Value Level of Significance High Moderate Low Biodiversity 49(81.66%) 7(11.67%) 4(6.67%) Aesthetic 17(28.33%) 38(63.33%) 5(8.33%) Recreational 15(25%) 4(6.67%) 41(68.33%) Scientific 51(85%) 7(11.67%) 3(5%) Educational 46(76.67%) 14(23.33%) 0 Water supply 55(91.67%) 5(8.33%) 0 Irrigation 12(20%) 42(70%) 6(10%) Groundwater Recharge 53(88.33%) 3(5%) 4(6.67%) Water Purification 0 16(26.67%) 44(73.33%) Flood Control 0 40(66.67%) 20(33.33%) Erosion Control 0 40(66.67%) 20(33.33%) Financial (fishing,grazing) 53(88.33%) 7(11.67%) 0
About the main human activities inside and around the site and their level of significance; from the respondents it can be observed that Agriculture(88.33%) and animal breeding(85%), extraction activity(71.67%)are the main human activitiesthat are at high level of significance, where as fishing and aquaculture(70%), tourism and recreation(86.67%),urbanization (75%) have low level of significance. Forestry (70%) and hunting (76.67%) are moderately significant. (Table22).
Table 22 : The main human activities inside and around the site and their level of significance Human Activity Level of High Moderate Low Significance Agriculture 53 (88.33%) 7 (11.67%) 0 Forestry 0 42 (70%) 18 (30%) Fishing and Aquaculture 15 (25%) 3 (5%) 42 (70%) Animal breeding(raring) 51 (85%) 7 (11.67%) 2 (3.33%) Hunting 0 46 (76.67%) 14 (23.33%) Urbanization 3 (5%) 12 (20%) 45 (75%) Tourism and Recreation 2 (3.33%) 6 (10%) 52 (86.67%) Extraction activities 43 (71.67%) 13 (21.67%) 4 (6.67%)
Respondents give the following reasons for those activities that had low status in the wetland; 53(88.33%) respondents replied there is lack of awareness and knowledge for aquaculture and 46(76.67%) respondents replied lack of infrastructures like fishing gears and decreasing volume of water level during dry season which results for the discontinuity of fishing activity, these conditions inhibit the farmers to participate exhaustively on these activities. For urbanization, 18(30%) respondents replied that; it is because the main city Dangila is located near so there is no burning issue for urbanization activity to happen there surrounding the wetland of course being started. For tourism and recreation, 40(66.67%) respondents stated that the area is not well known in this aspect, its components like birds are not taken in to considerations. At the same time the activity is unusual for people living around the wetland because most are engaged with other activities. For example even at the week-ends, they walk to the main town Dangilla for selling and buying different goods.
Discussion Water quality : There are differences in water quality among the three sites in the three seasons. This difference can be explained by different patterns of land use, pollution and forest cover of the 200 Ma nagement of shallow water bodies ..., EFASA 2010 investigated catchment areas. A century and a quarter of research on aquatic environment and wetlands has revealed close correspondence between physical and chemical conditions of water and the diversity, composition, and abundance of aquatic organisms. The seasonal deviation from the pH level of neutrality (<7) in the three sites could be due to the presence of acid forming compounds (humates) and humic acid formation due to decomposition of organic matter and the catchment could be contributory factor. There are different acid forming compounds such as nitrates and phosphates in the investigated wetland at varying levels. This might be caused when acid forming compounds were washed catchments (grazing land, agricultural land, etc decomposition, and leachates) to the wetland. The amount of DO in the water is directly related to the population size and community of aerobic bacteria the system can support (Jackson and Myers, 2002). Therefore, DO levels are an indicator of a water body’s ability to support aquatic life. According to U.S. Environmental Agency, DO > 5 mgL -1 is considered favorable for growth and activity of most aquatic organisms; DO < 3 mgL -1 is stressful to most aquatic organisms, while DO < 2 mgL -1 does not support fish life. Thus, when the mean concentration of DO measured at the three study sites and three sampling seasons is compared according to the standard set above, the concentrations in all sites and seasons, (Tables 4 and 5) are considered to be favorable for aquatic life, these sites were found to support fish species. At the outlet site two fish species namely Labeobarbus and Clarias garpinus /catfish species were recorded. The mean DO value is higher at the open water and outlet site during post rainy season. This may be due to presence of proper amount of light reaching at longer depth, resulting maximum photosynthesis ( high productivity) of macrophytes and phytoplankton so that more oxygen is produced. There is variation in temperature at the three sampling sites throughout the three sampling seasons. The vegetated wetlands are expected to have the lowest temperature because the wetland plants as well as the upland plantations cast shadow. This may slightly lower the temperature of the wetlands. In this regard, when the mean temprature recorded was compared among the three sites in the three seasons, it is apparent that the water temprature of the post rainy season (20.73 0c) could have been lowered due to cast by thick coverage of wetland plants. During this season, the macrophyte species richness as well as abundance were high as compared to the other seasons. In addition the highest mean temperature was recorded during the main-rainy season in the inlet water. This may be due to the presence of high run-off during this season in this siteas the effluents from non point sources are warmer than the wetland water itself. Electrical conductivity provides a measure of the total dissolved solids (TDS). The rise and/or fall of electrical conductivity is attributed to the dissolved solids in water (Bauder et al., 2003). Therefore, the total dissolved solid (TDS) contents are directly related to the electrical conductivity (Grattan, 2003). This fact holds true for the three sampling sites throughout the three sampling seasons where the change in total dissolved solids is directly related to the change in electrical conductivity. TDS is an important indicator of water quality and a major of determinant of aquatic habitat. It is striking that the three sites had comparatively low but still substantial conductivity. The higher mean conductivity seen (86.97 µscm -1) in the main-rainy season and (91.53 µscm -1) in the inlet site compared to the other two seasons and sites might be due to fertilizers runoff from the surrounding farmlands. There is high run-off during the main-rainy season entering to the wetland at the inlet site. The wetland has varying size and water levels at different seasons. It has standing water depths ranging between 0 and 1.35m (mean = 0.68m). Water transparency measured as Secchi-disk depth varied from 6cm to 53cm during the study period (mean: 29.5cm) and from 9cm to 10.3cm (mean=10.1cm) in the inlet water, from 13 to 53(mean = 34.67cm) in open water and from 6 to 31cm(mean 19.33cm) in outlet site (Table.5). In all the sites water transparency followed the same seasonal trend. The highest water transparencies were recorded in the post rainy season (mean 31.13cm) and the lowest (9.33cm) in the main-rainy season (Table.4). The transparency differences among stations are most probably due to the macrophyte density during the post rainy season which play a significant role in filteration of soil and trapping nutrients so that highest water transparency tare recorded and heavy sedment load from the agricultural farms found in the near vicinity during the peak rainy season result in lower transparency. 201 Ma nagement of shallow water bodies ..., EFASA 2010
Nitrates are highly soluble; therefore, they may quickly reach water bodies from soi1, organic matter, manures, etc. The nitrate concentrations in each site were low with mean values of 4.3, 2.52 and 2.13 mgL -1 for inlet, open water and outlet sites, respectively. When compared the three sites, the nitrate concentration was higher in the inlet site than the other two sites. Comparison of the mean nitrate concentration in the three seasons shows the main-rainy and the pre-rainy seasons had higher concentration than the post-rainy season.This difference could possibly be explained from artificial and natural fertilizers (plant residue and animal manures) runoff from non-point sources. This is because of the agricultural activities going on around Dibanko Bahir wetland applying compost manure as top dressing as well as the intensive grazing around the catchments. In general the overall nitrate levels observed in the investigated wetland were low. As studies indicate, phosphate tends to be fixed to soil particles and therefore reach water bodies when soil is eroded through geological and man–made (accelerated) erosions. Phosphates enter water bodies through man–made ways and contribute to surface water pollution due to algal blooms. According to Ayers and Westcot (1976) , the maximum allowable concentration of phosphate in irrigation water is 2 mgL -1. The mean concentration values of phosphate measured at the inlet, open water and outlet sites (Table 5) are all well below the recommended level to use the water for irrigation purposes. The occurrence of slightly high concentration of phosphate in the inlet site might be due to Wusafi River that carries domestic waste discharges and phosphate detergents to the site in addition to fertilizers’ runoff from the catchment. Generally as compared to nitrates, phosphates exhibit low concentration in each study site. Having the concentration ranges of 0.54 -5.2 mgL -1 and 0.9 – 1.28 mgL –1 for the nitrates and phosphates respectively indicate the wetland is not nutrient-limited. Flora: It is important to note that due to seasonal limitations, all flora species on the study area may not have been recorded specially during the dry season. This could be attributed to the extent of the site, plants being unidentifiable due to lack of fertile material, or plants lying dormant at the time of the survey. Table 6 shows the relative abundance (composition) of different macrophyte species in the wetland at each season. In all the seasons the Polygonum setulosum species was dominant over the other macrophyte species. Among those recorded in the pre-rainy season next to Polygonum setulosum species Aesschynomene abyssinica species was the next dominant (12%). In this season the least dominant was phragmites australis (0.1%). During the main rainy season among those recorded in the season next to Polygonum setulosum species, Aesschynomene abyssinica (12%) was the next dominant. The least dominant were three species namely, Phragmites australis , Perisicaria setosula and Crinum abyssinicum which is (0.1%). In the post rainy season next to Polygonum setulosum species it was the Trifolium acaule and Commelina benghalensis (8%) that were the dominant species. But the least dominant species in this season was Plectranthus puctatus (0.05%). Lastly in dry season, Juncus effuses was the most dominant (15%) and the least were Cyperus bipartitus and Perisicaria setosula (0.1%). This variation in macrophyte abundance may be due to sesonal variation in water level, nutrient availability and human disturbance level. Increased human disturbances in the surrounding wetland areas has been linked to altered hydrologic regime and increased water-level fluctuation and increased sedimentation and runoff contaminated water to wetlands (cf. Mitsch and Gosselink, 2002). Instability in the natural hydrologic regime combined with other artificial disturbances (e.g. nutrient input) may increase the potential for detrimental alteration of native plant communities (Mitsch and Wilson, 1996). For example, inputs of nitrogen and phosphorus especially in shallow freshwater bodies have led to considerable changes in the aquatic community structure, enhancing phytoplankton production, which in turn has caused suppression or complete disappearance of aquatic submersed macrophytes. The highest diversity (Shannon Weiner, 1.98) was measured in the Rush dominated community during the post rainy season and the highest species evenness (2.13) was observed in the Cyperus- dominated community site (Table 7).This variation in species diversity and evenness may be due to inaccessibility of the sites for maximum grazing. Since these two sites are near to the lodged water, farmers do not allow their livestock to graze in the lodged water due to fear of certain water-borne diseases. However, the first community (the grass land area) was excessively grazed and arren so that
202 Ma nagement of shallow water bodies ..., EFASA 2010 in this site the diversity index and evenness measured during dry season was 0. When the four seasons are compared for diversity, richness and evenness the highest value was observed in post rainy season (Table. 8). In this season there is optimum amount of water with good quality (more clear water for entrance of more light) resulting in maximum photosynthesis so that more diversity of plant species can survive. The highest biomass (18.84) and the least biomass (2.74) were also measured during the post-rainy season and the dry season, respectively (Table 9). This could also be explained as above. In all the seasons relatively Juncus effuses species showed higher biomass indicating that this species is more adapted to the wetland than the other macrophytes. As indicated in Table 9, in all the seasons Juncus effuses species had the highest biomass. The dominance of Juncus effuses over other species in all the seasons may be due due to its resistance to heavy grazing and other disturbances and/ or livestock preference to feed on other species more than Juncus effuses . Though the Polygonum setulosum species are abundant in number, their biomass was very low as compared to the Juncus effuses species, whichs may be again due to their suitability for grazing. Diferrent studies have indicated that intensity of grazing may affect species composition. Looyen ( 1984) and Bakker ( 1985) found that under heavy grazing pressure (cattle at 1.6 animals / ha = 11.2 SU/ha), forage selection depends on the amount of newly produced biomass not on its’ protein content and digestibility Therefore under heavy grazing, species that have recently produced biomass are more likely to be impacted. Birds: Among those bird species recorded the wetland was dominated by Black Crown Crane during dry season and Cattle Egret in pre-rainy, main rainy and post rainy seasons (Table 11). The wetland was the breeding and roosting site, especially for migratory birds like Black Crown Crane. The highest diversity index, H`, (1.659) and evenness, E (1.146) was observed during the post rainy season (Table13). The distinct seasonality of rainfall and seasonal variation in the abundance of food resources result in seasonal changes in the species abundance of birds (Popotnik and Giuliano, 2000). The distribution and abundance of many bird species are determined by the composition of the vegetation that forms a major element of their habitats. As vegetation changes along complex geographical and environmental gradients, a particular bird species may appear, increase or decrease in number, and disappear as the habitat changes (Popotnik and Giuliano, 2000). Human activities threaten the existence of many birds by destroying their habitat or directly affecting their survival and reproductive success. Benthic communities: Diifference in abundance of taxa of maco-invertebrates was observed between the three sites and the four seasons (Tables 14 and 15, respectively). Class Insecta had the highest (79.82%) abundance in the inlet whereas in open water and outlet , Oligocheata were abundant with the respective percentage, 47.01% and 59.8%. Table 16 shows that Class Insecta was abundant during the pre-rainy and post-rainy seasons whereas Oligocheata was abundant in the main- rainy season. Factors responsible for these differences are difficult to identify, but one conspicuous variable between seasons was water level. The summer had high precipitation and the increased water depth resulted in fewer submerged vegetation areas in the site. This lack of submerged sites could cause the submerged sites to appear less productive in terms of total numbers and total biomass of invertebrates than they actually are. This study implies that open sites tended to support larger populations (5524) relative to the other two sampling sites containing more surface area and available substrate (Table.18). Previous studies (Cyr and Downing, 1988; Beckett et al., 1991) have generally suggested that a relationship exists between large surface area of a macrophyte community and the high number of macro-invertebrates supported. The high number of insects found in open water samples can be explained by the large number of chironomid larvae found in the filamentous algae which dominated the bottom of open sites. Higher diversity index and eveness of invertebrate taxa were observed in the main rainy season (Table 18). Oligochaetea abundance was very large (46.62) during main-rainyseason (Table17). Productivity can vary greatly from season to season because of changes in mortality associated with population dynamics of major long-lived predators (e.g. Chironomid midge larvae). Socio-economic condition: Although a large proportion of households were found to be dependent on farming, more than 90% of their annual agricultural output was maize. The product is entirely used to
203 Ma nagement of shallow water bodies ..., EFASA 2010 serve at household level even without satisfying the households demand. Nevertheless, farmers in the wetland area are also so poor that they were allotting the wetlands to vegetable production to try to meet their cash needs. This practice was being carried out by draining the wetlands. Even the cash income from this source was not as such sufficient to satisfy their needs. One of the main reasons behind this deficit is the scarcity of farmlands in the areas concerned, which is also magnified by the lack of financial capacity to fulfill their demand for productivity. As shown in Table 21, the land holding size of the surveyed heads of households ranges from 0 to 2 hectares with respect to the land category. The overwhelming majority of the households (94.8%) owned perennial cropland with holding size between 0.1 and 2.0 ha as compared with the other category types. Having small size ownership in wetlands is mainly because the wetlands are considered to be public property, and are serving as the only grazing land area. In general there are confilicting activites among stake holders in the use of the wetland. Those farmers having little or no land holding from the terrestrial land and require to drain the wetlad and obtain farm land support drainage whereas those that use the wetland for grazing their cattle and women do not accept its drainage. Women contend that over-drainage can lead to the drying up of springs and they need to walk further to fetch springwater for drinking and have no other alternatives. The results in the survey study revealed that; the majority of households had livestock of different type. Statistical information in 2001 e.c obtained from the Kebele Agricultural extension office show that there are a total of 5,095 animals grazing on the wetland. Of these 4354 are cattle, 541 horses and donkeys and 200 sheep (Dangila Woreda Agricultural Office, 2001). All these are frequently grazing on the wetland. This showed that livestock rearing is entirely dependent on the wetlands under study as it is the main source of grass and water. The lives of people surounding the wetland are related to the activities associated with the wetland.This study found that the activities include rearing of animals grazing on the wetland, cultivation of crops/ vegetables/fruits using water from the wetland, daily collection of Cirpus validus from the wetland for the construction of local rain coat (in amharic Gessa) and fishing activity mainly in the previous years and use of water from the wetlands for sanitation purposes. Th wetland was found to support two fish species namely Clarias garpinus /catfish and Oreochromis niloticus (tilapia). In the pre-rainy season it was the Clarias garpinus /catfish which was dominant with an average count of of 13 per1hour catch effort, whereas starting from August during the main rainy season, Oreochromis niloticus became dominant, with an average count of 6 per1hour catch effort on the tributary rivers Botek and Branti. Most of those caught barbus fishes were females with maturity stage of 2-3 and weight between 4.5 and 6.2gm. In assessing the type of fish that have been known by the local people in the wetland; the presence of Clarias gariepnus (catfish) was confirmed by 70% and Barbus by 71.67% respondents. Only 10% of the respondents replied there were also other fish species. When asked which one was the most commonly harvested species.83.33% responded it was catfish ( Clarias garpinus ) whereas 16.66% it was the barbus species.This is may be because catfish is more available than the barbus fish. In assessing their opinion which species they like to eat, 91.67% respondents preferred Barbus species. Their reason for this is that the taste of barbus was more comfortable and to eat catfish is not as such culturally accepted due to its biological and physical appearance. 0nly less than 5%of respondents had no obligatory preference to consume any of the available fish species. In assessing the market condition of fish, households were also asked whether or not they sold fish, the survey result revealed that the vast majority of households (88.33%) never sell while only11.67% respondents sold fish. Reasons for those respondents to never sell were recorded in the following way; 3.33% of the respondents said they do not want to be engaged in such activity, 13.33% replired that though they wanted to sell, they did not know traders to receive their catch, 30% of the respondents said that although they were interested, they would have to bring the fish to traders and they were unable to do so or did not see any advantage in doing so.The rest 53.33% respondents replied that though they were interested in the activity, they did not have enough fish remaining after their own consumption.
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In assessing their opinion about the interest of people in eating fish, 65% of the respondents replied people living in this area were very interested in fish eating, 40% respondents stated people were interested in fish eating, 3.33% said that there were some people who were not interested in fish eating and the rest respondents (8.33%) replied there were people that were not accustomed to eating fish meat. When asked in which season or month they capture enough fish, 78.33% 0f respondents replied that it is during the entrance of main rainy season (June) and 21.67 % of the respondents stated that may be at the end of main rainy season.The production amount by each species is different at different time of the year depending on availability of the fish in the wetland. Although there are several advantageous in living near Dibanko Bahir wetland, also some disadvantages were aired from the respondents such that the wetland is highly susceptible to cattle diseases locally called ` `Gubet Beshita’’ , ( liver disease), leech attack and Biliharzia disease. Bad odor of the wetland and crop damage by wild animals such as birds, are also other disadvantages of living near the wetland. 100% of the respondents replied that there is not any monitoring procedure carried out in the wetland to establish and assess ecological changes (such as water quality) and no basic research was done on it. But the surrounding watershed, the Branti catchment water condition was assessed by one NGO. Though this NGO was trying to train the agricultural extension workers and some farmers about terracing and other conditions of the water system, it discontinue its activity for unknown reasons. But human activities in the catchments are expected to pose undesirable impacts on wetlands. Various kinds of human activities, for instance, grazing, is taking place in and around the wetland concerned. However, when the households were asked for their opinion on the overall human impacts, nearly 99 % of the households judged that human activities had no undesirable effects on the wetlands. Furthermore, when asked as to how they evaluated the status of the wetlands in their lifetime, 86.67% of the households stated that the wetland was minimizing in size and the possible causes were stated as the increase in agricultural activity. These accounted for nearly 67 % of the households’ possible reasons while around 30% said that they did not know the reasons. However, 66.67% of the households surveyed said that climatic changes such as drought on the wetland could contribute to the wetland’s changing conditions. With respect to vegetation cover over time on the wetland concerned, the survey indicated that the large majority of households (86.67 %) said that the vegetation cover on the wetland was decreasing. However, 10% of the households stated that the vegetation cover on the wetland concerned was increasing in wet season but decreasing in dry season. As shown in Table 19, the Land Use/Cover (LULC) Pattern of the wetland and its adjacent area, the total area coverd by forests was only (7.5%) as compared to the grassland coverage (80%). This may be due to massive agricultural expansion over the past 40 years that may lead to most natural areas being converted to grazing land. The negative impacts of such land use modifications may include declines in water quality and biodiversity.Studies have shown that there is a negative relation ship between land use intensity and wetland water quality and biodiversity. The strongest relationship tends to be with forest cover (Houlahan, 2002). In assessing the conditions of the wetland, households were also asked whether or not they used any chemical fertilizers or pesticides for the cultivation of crops around the wetland. The survey result revealed that the vast majority of households (88.33%) used these agricultural in puts whereas 10% of the households did not use them. Finally, the households were interviewed whether they fear that wetlands in their surrounding may one day disappear or not. The overwhelming majority of the households (89. 47 %) said that they have fear of disappearance of the wetland one day in the future as the result of human demand for the expansion of arable lands, while the remaining households said that the wetland would not disappear. In assessing their opinion about the conservation and regulation of this resource for sustainable utilization, majority of the respondents (68.33%) replied that since `we` are the first in taking the benefit, we should be aware of the risks of the wetland and should protect it. 31.67% 0f the respondents stated that the government should coordinate us to be engaged in such activity and so
205 Ma nagement of shallow water bodies ..., EFASA 2010 possibly involve in the management process. As stated above, the majority of households had no education background. This low level educational background of households might aggravate the unwise use of the wetland, and might also influence their understanding of the current status of the wetland due to detrimental impacts as a result of human activities.
Conclusion In this preliminary survey, the researcher observed that the original plain was covered in dense vegetation with small natural streams. However, massive agricultural expansion over the past 40 years has led to most natural areas being converted to grazing land. The climatic condition of the area is favorable for diverse species and the area has high socio-economic potential. Although it is not yet even partially quantified, a multitude of bird and plant species occur in the wetland. Indeed, the destruction or excessive modification of the wetland would result in the partial disappearence of some species. The record of 36 species of birds in this limited area shows that the diversity is very high. At the same time, the occurrence of winter birds in the area indicates that the area is important for migratory birds. The wetland also holds significant populations of some globally-threatened bird species. The Crown Cranes are probably the best “flagship” species for the wetland, covering much of the diversity. The present study suggests that there are qualitative and quantitative differences in macrophyte, bird, bentic macro-invertebrate and fish abundance and diversity among different seasons and sampling sites. It also implies that changing water levels play a large role in the abundance of certain organisms in the wetland ecosystem. Dibankobahir, with the inclusion of the adjacent dry land, is a major conservation priority for the villagers. It is probably the single most diverse wetland area and provides an excellent opportunity for holistic, landscape-based biodiversity conservation. But it is greatly degraded. Especially during the dry season the wetland starts to be completely out of surface water and it is used for permanent grazing. There are more than 5,000 animals grazing on the wetland. This poses a big threat for the survival of species and maintenance of diversity. In this area, there is no NGO engaged in the natural resource conservation and management activities. Yet, the governmental office responsible for these activities in place is the Dangila Woreda of Environmental Protection and Agriculture Office. However, in this office the total trained manpower is only three, of which one expert was assigned for the whole environmental protection activities, entirely focusing only on the control of deforestation. During this study, it was also understood that there were no local mechanisms in place to conserve the natural resources in general and the wetlands in particular in the area studied. This is an indication that conservation of natural resources has not been given due emphasis. However, when the households were asked whom they think should be responsible for managing the wetlands, the highest percentage of households(50%) rated the government as the most responsible body while 20% of the households rated the local community, and 30% rated both the local community and the government together are the most responsible bodies. However, it was understood from the survey that all of the households (100 %) had not seen or heard about any of the government effort to manage the wetland and the natural resources as a whole in their respective localities. Majority of the respondents (86.67 %) replied that they don’t have any awareness and any participation in the protection and conservation of the values of the wetland. Generally from the above responses one can understand that the sustainable use of Dibankobahir wetland and its values have not been given institutional recognition and the local community have no plans in mind except for its immediate use.
Recommendations In order to optimally manage a wetland marsh such as Dibanko Bahir, one must take the physico- chemical parameters of water quality, the plant communities, bird diversities, macroinvertebrate populations as well as the fish populations into account. In order to reverse the emerging problems and conserve this fragile but crucial wetland, immediate and appropriate action must be taken by the responsible stakeholders. This includes:
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• Water quality management measures like catchment treatment and controlling allochthonous nutrient loadings should be taken as soon as possible to stop euthrophication in the wetland. • Mobilizing all the stakeholders and special attention should be given to those where the wetland is found. • It is the right time to advance public awareness about the wetland and its values.
References Abebe Yilma and Geheb, K. (2003) .Wetlands of Ethiopia. Proceedings of a seminar on the resources and status of Ethiopia's Wetlands , VI + 116pp. Retrieved 19 December 2009 from www.iucn.org/themes/wetlands . Afework Hailu. (2005). Ethiopian Wetlands Distribution, Benefits and Threats pp 5-17 Proceedings of the Second Awareness Creation Workshop on Wetlands in the Amhara Region. Retrieved 19 December 2009 from www.iucn.org/themes/wetlands/ Abye Kindie. (2001). Wetlands Distribution in Amhara Region, Their Importance and Current Threats. An overview In: Proceedings of the Wetland Awareness Creation and Activity Identification Workshop in Amhara National Regional State. Ethio Wetlands and Natur Resources Association (EWNRA) Facilitated by the University of Huddersfield, UK January 23rd 2001 Bahar Dar, pp: 14-17. Bauder, T.A., R.M. Waskom, and J.G. Davis. (2003). Irrigation Water Quality Criteria. Colorado State university, U.S.A. Berka C., H. Schreier, and K. Hall. (2001). Linking water quality with agricultur intensificationin a rural watershed. Water, Air, and soil pollution 127 : 389-401. Chapion P.D and Reeves P.N. (2004). Effect of livestock grazing on wetlands: New Zealand. Cuffney T.F., M.R. Meader, S.D. Porter, and M.E. Gurtz. (2000). Response of physical, chemical,and biological indicators of water to a gradient of agricultural land-use in the Yakima river, Washington. Environmental Monitoring and Assessment 64 :259-270. Dangila Woreda Agricultural Office. (2001). Natural Resources Assessment of Dangila Woreda. Ministry of Agriculture, ANRS, Ethiopia. Daracon Quarries. (2007). Proposed Ardglen Quarry Extension Flora and Fauna Assessment. Australia Dixon, A.B. and Wood, A.P. (2003). Wetland Cultivation and hydrological Management in eastern Africa: Matching community and hydrological needs through sustainable wetland use. Natural Resource Forum 27 :117-129. Dugan, P.J. (1990). Wetland conservation: A Review of Current Issues and Required Action. IUCN, Gland, Switzerland. Retrieved 19 October 2009 from www.iucn.org/themes/wetlands/ Edwards, S. (1976). Some wild flowering plants of Ethiopia . Addis Ababa University press. Ethiopia. Environment Southland. (2002). State of the Environment Report for Water. EWNHS, Ethiopian Wildlife and Natural History Society. (1996). Important Bird Areas of Ethiopia: A First Inventory, EWNHS, Addis Ababa , PP 300. Erin Fehringer. (2005). Wetland Rapid Condition Assessment: Development, Testing and Analysis. America. Fichtl, R. and Admasu Adi. (1994). Honey bee flora of Ethiopia . Addis Ababa, Ethiopia. Grattan, S.R. (2003). Irrigation Water Salinity and Crop Production. University of California. Gete Zeleke. (2001). Lessons and challenges of Agricultural research in Amhara Region: Advice for future research work on wetlands : Proceedings of the wetland awareness creation and activity identification workshops in Amhara National Regional State, BahirDar : pp 18-20. Goraw Goshu. (2008). The physico-chemical characteristics of a highland crater lakeand two reservoirs in north-west Amhara region (Ethiopia). Ethiopian Journal of Science and Technology Bahir Dar University . In press. Hayal Desta. (2006). Environmental, Biological and socio-economic study on Boye and extended wetlands in Jimma Zone of Oromia National Regional State, southwest Ethiopia. Addis Ababa University School of Graduate Studies, Department of Environmental Science. Ethiopia.
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Hillman J. C. and D. A. Abebe. (1993). Wetlands of Ethiopia. In: Ethiopia: Compendium of Wildlife Conservation Information (ed. J. C. Hillman). NYZS -The Wildlife Conservation Society International, New York Zoological Park,Bronx, NY and Ethiopian Wildlife Conservation Organisation, Addis Ababa, 2 Vol.s 786 pp. Retrieved 19 October 2009 from www.iucn.org/themes/wetlands/ Houlahan, J. E. (2002). The effects of adjacent land-use on water quality and biodiversity in southeastern Ontario wetlands. Jansen, A.; Healey, M. (2003). Frog communities and wetland condition: relationships with grazing by domestic livestock along an Australian floodplain river. Biological Conservation 109(2) : 207-219. Keddy, P.A. (2000). Wetland Ecology principles and conservation . Cambridge Studies in Ecology, Cambridge University Press, England. 614 p. Leibowitz, S.G. (2003). Isolated wetlands and their functions: An ecological perspective. Wetlands 23 :517–531 Mengistu Wondafrash. (2000). Wetlands, birds and important bird areas in Ethiopia: an overview. In: proceeding of a seminar on the resources and status of Ethiopia’s wetlands . PP.12-17. IUCN- The World Conservation Union Nairobi, Kenya.Retrieved 19 October 2009 from Htt://www.wetlandaction.org McFartand A.M.S. and L.M. Hauck.(1999). Relating agricultural land-uses to in-stream stormwater quality. Journal of environmental quality 26 :836-844 Menard, C.; Duncan, P.; Fleurance, G.; Georges, J.; Lila, M. (2002). Comparative foraging and nutrition of horses and cattle in European wetlands. Journal of Applied Ecology 39(1) : 120-133 Merrit and Commons (1996). An Introduction to Aquatic Insects of North America. USA. Middleton, B. (2002). Non-equilibrium dynamics of sedge meadows grazed by cattle in southern Wisconsin. Plant Ecology 161(1) : 89-110. Mitsch, W.J. and J.G.Gosselink (2002). Wetlands. 3rd ed, John Wiley and Sons, Inc. U.S.A. Olson, E. Engusroma. E; Doeringsfeldb, M. and Bellig, R.(1993). The Abundance and Distribution of Macroinvertebrates in Relation to Macrophyte Communities in Swan Lake, Nicollet County, MN Department of Biology Gustavus Adolphus College St. Peter, MN 56082 USA Parkyn S.; Matheson, F.; Cooke, J.; Quinn, J. (2002). Review of the environmental effects of agriculture on freshwaters. NIWA Client Report FGC02206, Hamilton. 45 p. Popotnik, G.J. and Giuliano, W.M. (2000). Response of birds to grazing of riparian zones. Journal of Wildlife Management 64(4) : 976-982. Schuyt, K. (2004). The Economic values of the world’s Wetlands. WWF-International, Gland, Switzerland. Shannon, C.I. and Wiener, W. (1949).The mathematical theory of communication . Illinois books, Urbana. Steinman, A.D.; Conklin, J.; Bohlen, P.J.; Uzarski, D.G. (2003). Influence of cattle grazing and pasture land use on macroinvertebrate communities in freshwater wetlands. Wetlands 23 (4) : 877-889. Tanner, C.C. (1992). A review of cattle grazing effects on lake margin vegetation with observations from dune lakes in Northland, New Zealand. New Zealand Natural Sciences 19 : 1-14. Terry, S. and John, F. (2004). Field guide to the birds of East Africa Kenya Tanzania Rwanda Burundi. London. Timberlake, L. (1985). Africa in Crisis: The Causes, the Cures of the Environmental Bankruptcy . Earthscan. London 218pp Tiner, R.W. (2003). Geographically isolated wetlands of the United States. Wetlands 23 :494–516. U.S.Environments Protection Agency. Wetlands. Retrieved 19 december 2009 from http://www/epa.gov/owow/wetlands/vital/what. html
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Van Hoewyk, D.; Groffman, P.M.; Kiviat, E.; Mihocko, G.; Stevens, G. (2000). Soil nitrogen dynamics in organic and mineral soil calcareous wetlands in eastern New York. Soil Science Society of America Journal 64(6) : 2168-2173. Wardle, P. (1991). Vegetation of New Zealand. Blackburn Press, USA. 672 p. WCED (World Commission of Environment and Development), (1987). Our Common Future. WCED. Oxford University Press. New York, U.S.A. 398pp. Zemede Asfaw and Mesfin Tadesse. (2001). Sustainable use and development of wild food plants in Ethiopia. Economic Botany 55 : 47–62
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Anthropogenic impacts on rift valley waterbodies: the case of Lakes Zeway, Langanoo and Abijata
Mathewos Hailu, Getachew Senbate, Megersa Hindabu and Birhanu Tadese Zeway Fisheries Resources Research Center, P.O box 229 Zeway, Ethiopia
ABSTRACT : The Ethiopian central rift valley encompasses a series of lakes, rivers and wetlands with high socioeconomic importance to the country. This study focused on the central rift valley which encompasses Lake Zeway, Langanoo and Abijata located 38 o00’-39 o30’ E and 7 o00’-8o30’ concentrating on the districts around the lakes. Community perception and users attitude was assessed regarding the lakeside environment including vegetation cover (past and present ), water utilization, economic benefit, type of agrochemical utilization and fisheries management, etc. The economic benefit from Lake Zeway was mainly from fishing and water extraction for irrigation with the irrigated farms’ production of horticulture including flower farming covering 500 ha. Lake Abijata was mainly used for soda ash production and mineral salt for livestock as means of income as revelealed by 12.5 % households.. In Lake Langanoo, the water was used by the local community for fishing and livestock as well as home consumption. However the areas surrounding the lakes are fragile ecosystem, which are facing threat from irrigated agriculture, improper water abstraction in line with population increment. Expansion of farmland by 50 % around Lake Langanoo has aggravated the deforestation activity. Absence of regional fisheries policy has encouraged the involvement of 27.7% and 7.7%, illegal fishermen in Lake Zeway and Lake Langanoo respectively. The existing cooperatives do not have clear cooperative structure.96 % of the beach seine in Lake Zeway is below the recommended mesh size. Overall problems in fishery production were indicated as illegal fishery (58.6%), followed by inappropriate mesh size of 31.0%. The absence of soil conservation practice accelerated siltation process in Lake Abijata. Lack of regulation has aggravated the use of extremely toxic pesticides including endosulfan that is used in proximity of Lake Zeway. Despite the existence of institutional environment regarding water and environment, government rules are hardly implemented at local level. This paper reviews some of the adverse socioeconomic activities that exert pressure around the lakeside environment.
Key words : Abijata, Anthropogenic impact, environmental degradation, Zeway, Langanoo, Rift valley, water abstraction.
Introduction The Great Ethiopian rift valley which bisects the southern highlands into half stretches more than 600 km NNE of the Kenyan border to Koka dam of Ethiopia and then diverts before it widens and falls to below sea level in the Afar Depression, from which rifting continues to the Red sea coast (Tudorance, et al., 1999). The Ethiopian rift encompasses a series of lakes, stream and wetlands with unique hydrological and ecological characteristics (Wood and Talling, 1988; Elisabeth, et al ., 1996). In addition to this, the central rift valley has a total population of approximately 1.5 million with an average population of 1.5 per hectare (Jansen, et al., 2007). In Ethiopia, water quality is strongly influenced by human factors in combination with the geology, warm climate, and physiographic factors such as rugged terrain, through effects on rates of mineralization, soil erosion and transport of particulates and solutes (Zinabu et al ., 2002). These lakes are in the vicinity of fast growing cities surrounded by agricultural land, and exposed to water quality changes as a result of land use and modification, irrigation (Zinabu, 1998). Lake Zeway is being used for a variety of developmental activities such as fisheries, irrigated agriculture (commercial farming), cattle watering, human sanitation, etc. (LFDP, 1993; Jansen et al., 2007). The nearby growing town of Zeway also contributes some urban wastes via run off. The lake also supports commercial fisheries of Oreochromis niloticus , Tilapia zillii , Cyprinus carpio and Clarias gariepnus. Lake Langanoo is serving as an ecological tourism, fishery and potable water source for human and livestock around the area. Lake Abijata is mainly limited to tourism and soda ash extraction (Tilahun et al., 1996; Tenalem, 2002).
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The growing population of the rift valley had led the natural vegetation to be transformed into agricultural land (Zerihun et al., 1990; Feoli et al., 2000). Water levels of the rift valley lakes are decreasing from time to time (Tenalem, 2004). Fish production has become a victim of this change in lake water levels and water chemistry. The decline damages the breeding grounds of fish species that spawn in shallower parts of the lake (e.g., Oreochromis niloticus , the most important species commercially). These effects are magnified in shallow lakes like Zeway, where a higher rate of water level fluctuation has been observed (Zinabu, 1998). The open access characteristic of the fishery in the region increases the number of fishermen, which in turn leads to stock depletion (Felegeselam, 2003). This study aimed at assesing human activites in the areas that are affecting the ecology of the lakes and the opinion of the community towards these resourses.An understanding of these separate activites in these places is essential for policy makers and implementers in order to avert ecological crisis and problems .
Materials and methods Study area: This study focused on the central rift valley which encompasses Lake Zeway, Langanoo and Abijata (Fig. 1.) located 38 °30’-39 °05’ E and 7 °30’-8°15’ concentrating on the districts around the lakes. The basic hydrology of the lakes is given in Table 1).
Fig. 1. Map of the study area (Source: Jansen et al ., 2007) ( the study focused on the dot-encircled area )
Table 1.Basic hydrological data of the lakes (source: Wood and Talling ( 1988); unless indicated otherwise) Altitude m. Maximum Mean depth Lake Lake area a. s. l depth (m) (m) Zeway 1636 442 8.95 2.5 Langanoo 1582 241 47.9 17 Abijata 1578 95 a 14.2 7.6 a (Jansen, et al., 2007) Data collection : Questionnaires were prepared to investigate the socio-economic benefits the surrounding people were getting from the near by waterbodies. The residents’ attitude towards the lake side environment, including vegetation cover (past and present ), water utilization, type of agrochemical
211 Ma nagement of shallow water bodies ..., EFASA 2010 utilization and fisheries management, fishing gear utilization, etc, were reviewed. Secondary data were also collected from the nearby districts. The data was analyzed using SPSS.
Result and Discussion Socio economic importance of the lakes: Located in the central rift valley these lakes have ample socioeconomic importance to the local and national economy. The economic benefit from Lake Zeway was mainly from fishing and water extraction for irrigation. During data collection period in 2007, a total area of 3700 hectare land was cultivated with abstraction of lake water; these irrigated farms provided employment for thousands of people. The lake also provides water for domestic use and the fishery of the lake is also an important source of livelihood to the fishermen community. The lake ecosystem falls within the natural tourist attraction sites especially that of birding. Despite its delineation in Abijata – Shala National park , a number of people reside within the park area of Lake Abijata. Due to its water chemistry, there is no fishing activity in Lake Abijata and the nearby residents reported the total collapse of the fishery after the year 2001. The households from Abijata responded that only 12.5% are getting economic benefit from the lake in the form of “Boji” mineral salt which is used as ’salt lick’ for livestock. Local people extract the mineral salt during dry season for salel. The mineral salt was extracted from the area of the lake where water has receded. The lake also supported soda ash production. There was also illegal sand production in the southern part of the lake. In Lake Langanoo, the water was used by the local community for fishing and livestock as well as home consumption. There are also different hotels and lodges making the lake tourist attraction site. AtLake Langanoo, water is not used for irrigation due to its salinity, The households preferred the economic benefit from the nearby land than the fishery, which has led to farm expansion by the households, which in turn has contributede to the deforestation activity. The human impacts on the lakes are linked to the many social and economical activities by numerous stakeholders found within the lake basin. These impacts include improper water utilization, destruction of lake side vegetation and improper fishing. The fishery activity in the central rift valley is currently restricted to Lake Zeway and Langanoo. Previously, fishing activity was also practiced both legally and illegally at Lake Abijata but the observation at the site and response from the local community indicated that the current water chemistry related to the decrement in water level associated with the receeding of the lake have resulted in phasing out of the fishery in the lake. As fishing in the region does not have a policy, the fishing activity is being undertaken by both legal and illegal fishermen. When considered from their enrollment in one of the near by cooperatives, 27.7% of Lake Zeway and 7.7% Lake Langanoo fishermen don’t have membership Id due to various reasons. However these data do not show the increased number of illegal fishermen during fasting season. One of the amazing scenarios at both lakes is that enrollment in cooperatives was highest in the past 10- 20 years before present (64%), due to efective monitoring done by the Ministry of Agriculture in that time. The existing cooperatives do not have clear cooperative structure with no saving mechanism t lake Langanoo and while 60% of cooperatives participate in saving within cooperatives at Lake Zeway. The main reason for the enrolment of the fishermen in the existing cooperatives, especially in Lake Zeway, is fear of spontaneous control by the Districts Bureau of Agriculture officers. Dependency only on fishing activity is higher at Lake Zeway with 67% of the fishermen, and less at Langanoo with only 34% totally dependent on fishing. These may be due to the market problem of Lake Langanoo relative to Lake Zeway and having more arable land than those at Zeway. Fishing gear operation in both lakes was undertaken by beach seine, gillnet and long line(Fig. 2
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Fig. 2: Fishing gear preference by fishermen at Lake Zeway and Langanoo
The fishery in Lake Zeway is mainly undertaken by beach seine taking under consideration the recommended mesh size of 80 mm stretched mesh size. 96 % of the fishing gear is below standard leading to harvesting of juvenile fish. The same scenario was also observedin Lake Langanoo. The major problem regarding beach seine utilization was that the fishermen usually tend to minimize the stretched mesh size of the code end leading to harvesting juvenile fish.65% of the fishermen at Lake Zeway stated that associated with smaller mesh size beach seine fishing gear available to them is highly destructive to the sustainability of the fisheries. However 70% of fishermen at Langanoo indicated that there was nothing called destructive fishing gear if properly used. The fishermen stated that the overall problem to the decline in the fish stock was mainly due to illegal fishery (56 %) (Table 2 ), pointing out the necessity of fishing policy for the region.
Table 2: The overall problems in fishery production of Lake Zeway and Langanoo
Overall problem in fishery production Percent Pollution 17 Illegal fishery 58.6 Inappropriate mesh size 31.0 Wetland degradation 17.2 Unavailability of fishing gear 13.8 Inappropriate marketing system 41.4
Impact on lakeside vegetation: The main vegetation type in the study area consists of drought resistant trees and shrubs either deciduous, or with small, evergreen leaves. The dominant tree species are Acacia spp. mainly Acacia tortolis, Acacia albida and Acacia seyal .The woodland cover in the central rift valley is alarmingly depleted through cutting for fuel wood, construction wood and charcoal associated with the growing population in need of farm land.The acacia woodland is found mixed with farm plots. The area is degraded due to the disturbance, habitat loss and competition with domestic animals for forage. The Participatory Rural Appraisal type assessment for the vegetation condition before ten years around the three lakes indicated the presence of) vegetation types which used to be dominant around the various localities of the lakes (Table 3. The main reason mentioned by the respondents for the aggravation of deforestation especially on the dominant Acacia spp in the area are due to fuel wood, construction wood, charcoal demand for agricultural land by the growing population. Construction wood is used for construction of fence, barn as well as local house. Mostly the branch of Acacia trees are used for construction of barns and fences around Abijata and in Langanoo, the use of Annano ( Euhorbia Scoparia) for fencing has minimized the use of direct tree cutting which is also serving in the forestation process. 213 Ma nagement of shallow water bodies ..., EFASA 2010
Table 3. Plant species around the three lakes that have been highly impacted
Zeway Abijata Langanoo Acacia albida Acacia tortolis Acacia albida Acacia seyal Acacia saginata Acacia tortolis Acacia tortolis Acacia seyal Balanties aegiptica Balanties aegiptica Croton machrostachys Dodena viscosa Mytnus ovatus Ficus sycomorus Ficus sycomorus Ficus lutea Ficus lutea Mytnus ovatus Rhus natalenus
Unlike fuel wood and construction which uses the branches of trees, charcoal production requires the use of the main stem leading to complete cut down of trees. Production of charcoal as cause for deforestation constituted 58.35%, 46.45% and 50% of the respondents from Lakes Zeway, Abijata and Langanoo, respectively.The study area is an important charcoal production area because of its acacia trees. It serves as subsistence income for the households and it is the main source of energy for the nearby towns and cities. House wives are engaged in the production of charcoal while young brokers around the main road are involved in its salel. The possible mitigation mechanisms suggested by the community were forestation (52%), preventing deforestation (32%) and creating of job opportunities (16%). Despite the high amount of soil erosion estimated to be between 51-100 t/ha by Halcrow (2007) around Meki watershed, there was no soil conservation practice observed in the study area .Agrochemicals utilization: One of the main factors in water pollution around Lake Zeway is the unwise utilization of agrochemicals especially that of pesticides. The survey indicated that 100% of the irrigated horticulture farmers utilize different type of agrochemicals ( Table 4). The pesticides are applied more than 20 times during the three months of cultivation.
Table 4. Agrochemicals utilized in proximity of Lake Zeway by open irrigation farms. Trade name Active ingredient Agro –THOATE 40% EC Dimetoae 40% w/v Apron ® Star 42WS Thimethoxam 20 % ,Difenconazole 2 % ,Metalxyl 20 % Bumpers 25 EC Propiconazole 250 gm/l DDT Diazole 60 EC Diazone 60 % HELCOZEB 80 WP mancozeb KARATE 5 EC Lambda-cyaltorin 50 gm/l Kocide 101 Couper hydroxide 77% THIONEX® Endosulfan 350 gm/l Malatine MANCOLAXYL 72 WP Metloxyl 80 g/kg , mancozeb 640 g/kg Metosystox NIMROD 25 EC Bumpirimate 250 g/l Nobel 25 WJ Propiconazole 250 gm/l Pyrinex 48 EC Chloroform 48 % RIDOMIL Gold MZ 68 WG Mefenoxam (metalaxyl –M)-40g ,mancozeb 640g/kg SELECRON®720 EC Profenofos 720 gm/l
The pesticides KARATE 5 EC, RIDOMIL Gold MZ 68 WG, Apron ® Star 42WS and SELECRON®720 EC have clear labels on their leaflets indicating that they may be toxic to fish and bees and indicate 214 Ma nagement of shallow water bodies ..., EFASA 2010 caution to be taken in their application; however they are being utilized in irresponsible manner in farms as close as two meters to the lake. Water use: Lake Zeway water is utilized mainly for irrigation, livestock drinking and household consumption. The irrigation mechanism in Lake Zeway is by individual farmers, water user associations and large scale investors. The feeders of Lake Zeway, the Katar and Meki rivers have an average annual flow of 392 x 10 6 m3 297 x 10 6 m3 respectively and the outflow through Bulbula river 184 x 10 6 m3 (Tenalem, 2002). The irrigation activity which was mainly undertaken by small water pumps concentrated in the western part of Lake Zeway. The use of various types of water pumps, difference in time and use of these pumps and their distribution makes it difficult in determining the amount of water extracted from the lakes however, according to Jansen et al ., (2007) the average annual irrigation water use was 20,000 m 3 ha . -1 based on crop water reqirment. Considering the amount of the irrigated farms in 2007 from Lake Zeway, the water abstraction was estimated to be 74x 10 6 m3. The annual evaporation for Lake Zeway was estimated to be 619 Mm 3 (Jansen et al ., 2007). The water balance of Lake Abijata is controlled by river discharge, rainfall and evaporation. Water levels in Lake Abijata were very low during most of the period of this study, and the water receded more than 400 m within a year in 2007 from its average shore line (Fig. 3.). Of the two inflows, the Horakalo had been dry for more than eight months but Bulbula River was continuously flowing during the whole study period. The Abijata soda ash factory was established in 1990. Soda-ash is produced by evaporating the lake water in large ponds. The amount of water abstracted from the lake is 13 X 10 6 m3/annum. The outflow of Lake Zeway through Bulbula River was utilized by 160 ha farmland before it reached Lake Abijata. This has its own impact on the fluctuation of Lake Abijata. The water balance of Lake Abijata is indicated in Table 5).
Fig. 3. The receded area of Lake Abijata, 2007.
Table 5: The estimated annual water balance of Lake Abijata in 10 6 m3 (source: (Tenalem, 2002).)
Conventional water balance : Ground model : Pl Ri +Sr E A Gi-Go Gi Gi-Go 113 245 372 13 27 27 26 Ri=inflow from rivers, Sr=surface water flow from ungaged catchments, E=evaporation, A=abstraction for soda ash, Gi=ground water inflow, Go=ground water outflow
The land that the water has receded is needed for grazing land at Lake Abijata and for sand extraction in Lake Langanoo, without taking into consideration the ecological impact that reduction in water has on ecosystem
215 Ma nagement of shallow water bodies ..., EFASA 2010
Conclusion Human activity in rift valley should be in a sustainable manner as the environment is highly fragile and water level of the lake seems to be influenced by both human activity and climatic factors. Most of the interviewed farmers are aware of the fact that clearing of forests has basic impact on climatic change, but unless employment opportunities are diversified, the clearing of forests as a source of revenue for production of charcoal would not stop. Fisheries resource currently lacking policy in the region has led to increment of illegal fishing activity though Kelil ( 2002) reported that the fishermen are willing to participate in regulatory mechanisms. Human pressure is high in the central middle rift valley and natural vegetation is disappearing rapidly. Anthropogenic pressure has resulted in open canopy vegetation which is floristically poor. According to Feoli and Zerihun, (2000), Acacia seyal and Acacia tortolis will re-colonize the floor of the rift valley when anthropogenic pressure is relaxed for at least 15 years. This event is observed in some protected areas of the rift valley. High population increases over the limited land area has resulted in the indiscriminate forest clearing and overgrazing around the lakes. The absence of soil conservation practice has accelerated siltation process in Lake Abijata. To understand the impact of the pesticides in the lake ecosystems, detailed study is necessary in order to mitigate the problem. Despite the existence of institutional environment regarding water and environment, government rules are hardly implemented at local level. This has led the natural resource to be seen as open access resource in the area.
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