Study of Biology and Population Dynamics of Exotic Fishes Oreochromis Mossambicus and O.Niloticus from Keenjhar Lake (Sindh) Pakistan

STUDY OF BIOLOGY AND POPULATION DYNAMICS OF EXOTIC FISHES OREOCHROMIS MOSSAMBICUS AND O.NILOTICUS FROM KEENJHAR LAKE (SINDH) PAKISTAN.

ATIA BATOOL

DEPARTMENT OF ZOOLOGY UNIVERSITY OF KARACHI KARACHI-75270

STUDY OF BIOLOGY AND POPULATION DYNAMICS OF EXOTIC FISHES OREOCHROMIS MOSSAMBICUS AND O. NILOTICUS FROM KEENJHAR LAKE (SINDH) PAKISTAN

ATIA BATOOL DEPARTMENT OF ZOOLOGY UNIVERSITY OF KARACHI KARACHI-75270

STUDY OF BIOLOGY AND POPULATION DYNAMICS OF EXOTIC FISHES OREOCHROMIS MOSSAMBICUS AND O. NILOTICUS FROM KEENJHAR LAKE (SINDH) PAKISTAN

SUBMITTED BY

ATIA BATOOL

DEPARTMENT OF ZOOLOGY

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN LIMNOLOGY AND FRESH WATER FISHERY BIOLOGY, DEPARTMENT OF ZOOLOGY, UNIVERSITY OF KARACHI

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CERTIFICATE UNIVERSITY OF KARACHI FACULTY OF SCIENCE

This thesis entitled “Study of Biology and Population dynamics of exotic fishes Oreochromis mossambicus and O. niloticus from Keenjhar lake (Sindh) Pakistan.” Submitted by ATIA BATOOL is accepted by the Department of Zoology, University of Karachi, as satisfying the thesis requirement for the degree of Doctor of Philosophy (Ph.D) in Zoology.

Supervisor ______Dr. Sumera Farooq Assistant Professor Department of Zoology University of Karachi.

Chairman ______

Department of Zoology University of Karachi. Karachi,Pakistan. Dated : 26th December 2017.

Author’s declaration

I, Atia Batool, a student of Department of Zoology, University of Karachi, do hereby solemnly declare that this thesis entitled “Study of biology and population dynamics of exotic fishes Oreochromis mossambicus and O. niloticus from Keenjhar lake (Sindh)Pakistan.” Submitted as partial fulfillment of the requirement for the degree of Doctor of Philosophy is my original work and has not been submitted in any version thereof for assessment in any other subject /University/institution and shall not in future be submitted by me for obtaining any degree / diploma from other University / institution.

Atia Batool Lecturer Department of Zoology University of Karachi.

Dated: 26th December 2017.

Plagiarism Undertaking

I Solemnly declare that research work presented in the thesis titled “STUDY OF BIOLOGY AND POPULATION DYNAMICS OF EXOTIC FISHES OREOCHROMIS MOSSAMBICUS AND O. NILOTICUS FROM KEENJHAR LAKE (SINDH) PAKISTAN” is solely my research work with no significant contribution from any other person. Small contribution/help wherever taken has been duly acknowledged and that complete thesis has been written by me.

I understand the zero tolerance policy of the HEC and University of Karachi towards Plagiarism. Therefore, I as an Author of the above titled thesis declare that no portion of my thesis has been plagiarized and any material used as reference is properly referred/ cited.

I undertake that if I am found guilty of any formal plagiarism in the above titled thesis even after award of Ph.D degree, the University reserves the rights to withdraw/revoke my Ph.D degree and that HEC and the University has the right to publish my name on the HEC / University Website on which names of students are placed who submitted plagiarized thesis.

Student/Author Name: Atia Batool

Student/Author Signature:______

Supervisor Name: Dr Sumera Farooq

Supervisor Signature:______

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TABLE OF CONTENTS Page No.

ACKNOWLEDGMENT…………………………………………………….………x

Abstract…………………………………………………………………xi

Khulasa…………………………………………...……………………xiv

List of Tables………………………………………………………...... xvi

List of Figures…………………………………………………..……..xix

1. INTRODUCTION…………………………..……………….…1-5

2. MATERIAL AND METHODS…………………………..… 6-11

2.1 Study site………………………………………………………………….7 2.2 Data collection…………………………………………………………… 8 2.3 Morphometrics…………………………………………………….……. 8 2.4 Biological study………………………………………………...... 9 2.5 Fishery Status…………………………………………………………...10 2.6 Statistical analysis……………………………………………………….12

3. RESULTS…………………………………………………………..….13-84

3.1 Variations in Length-Weight of O. mossambicus and O. niloticus…...13 3.2 Condition factor (Kn)…………….……………………...... 26 3.3 Observation of gonads and length composition of O.mossambicus and O.niloticus……...…………………………………...………...... 29 3.4 Observation of gonads and weight composition of O.mossambicus and O. niloticus………………………………...………………………..35

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3.5 Monthly variation in maturity stages of O. mossambicus...... 43 3.6 Monthly variation in maturity stages of O. niloticus……………..46 3.7 Fecundity……………………………………………...... 49 3.8 Morphology of gonads………………………..………...... 50 3.9 DSI (Digestosomatic index)…………………..……………...... 57 3.10 Relation between GSI and DSI……………………………………...59 3.11 Catch composition and fishery status………………………………61 3.12 Variations in relative abundance of O. mossambicus and O. niloticus in total catch……………………………………….………72 3.13 Variations in relative weight of O. mossambicus and O.niloticus in total catch………………………………………………………..76 3.14 Growth performance and population estimation……….…… 80

4. DISCUSSION……………………………………….………..88-93

5. CONCLUSION……………………….……………...……...94-95

6. FUTURE RECOMMENDATIONS……………………………95

7. REFERENCES……………………………………………..96-110

8. APPENDIX………………………………………………. 111-112

9. PUBLICATION…………………………………..…………....113

ACKNOWLEDGMENT

My deep reverence goes to Almighty Allah, my supreme, who enabled me to complete the present work.

I am thankful to my respected supervisor Dr Sumera Farooq for her support, guidance and encouragement.

I am greatly thankful to respected Prof. Dr Arshad Azmi (Chairman) for his support and for minimizing my workload at Zoology Department, University of Karachi as I got enough time to complete this research work.

I am also acknowledged to respected Prof. Dr Farida Begum for her encouragement and support.

I would like to thanks Prof. Dr Upali S. Amarasinghe, University of Kelniya, Sri Lanka, for his guidance and support during research.

I am very much thankful to all fishermen who supported me in the collection of samples from fish landing sites for this research work.

I am very much thankful to my mother for her prayers for me and other family members specially my husband Muhammad Safeer and brothers for their support in collection of samples from fish landing sites during this research work.

I want to express my deepest gratitude to all, those help out and support me for completion of this work specially my brother Adnan Mehmood(Dani)

ABSTRACT

Keenjhar Lake is one of the largest freshwater lakes in Pakistan. It was declared Wildlife Sanctuary in 1977 under Sindh Wildlife Protection Ordinance, 1972. It is a Ramsar site and also known as Kalri Lake. In Pakistan two exotic species Oreochromis mossambicus and O. niloticus show wide range of expansion and prolific colonization in most freshwater and saline inland waters of Pakistan.

The specimens and data were collected from the landing site Khambo at Keenjhar Lake twice in a month for three years (January 2014- December 2016). A total of 43200 specimens were examined during three year period. The total length (TL) and weighed (TW) were measured. For the study of Length-weight relationship (LWR) the collected length-weight data was transformed logarithmically. The Length-weight relationship (LWR) and condition factor of fish was determined. For the biological study 2880 mature specimens of O. mosambicus and O. niloticus were examined for the determination of length, weight, sex, maturity stage, fecundity, GSI and DSI according to prescribed methods. Only ovaries of maturity stage (IV,V and VI) were preserved in Gilson’s fluid. The eggs were counted and weighed. For the calculation of gonadosomatic index (GSI) and digestosomatic index(DSI), the fishes were dissected and the weight of gonads and the weight of digestive tract was noted in grams. Asymptotic length (L ), growth constant, (K), growth performance index(GI), total mortality(Z), natural mortality(M), Fishing motality (F), exploitation rate( E) and maximum exploitation rate (E max) were calculated. For the determination of fishery status, the data from landing site Khambo was collected monthly. Species diversity and their catch in kilograms were recorded from each boat. The natural mortality, total mortality and fishing mortalities were determined. Regression analysis and One- way ANOVA was performed to test the length-weight relationship.

The TL and weight in both sexes ranged between 11-28 cm and 17 to 430 g in O. mossambicus and from 11- 29.5 cm and 27 – 430 g in O. niloticus. The value of regression coefficient b of O. mossambicus and O. niloticus was 2.7 and 2.975 respectively. The comparison of length-weight data indicated that the range of length remains same between the studied years in contrast to weight which shows increasing

trend. The GSI values of both sexes of both species were low in contrast to DSI values which was high in both species. The data indicates that O. mossambicus and O. niloticus spawn throughout the year. O. niloticus show two recruitments per year. Sex ratio is almost similar (1:1) in both species which do not appears to affect the fish population. The peak spawning months in male and female were different which might cause negative influence on the fish population. Overall the data collected during 2014 and 2016 shows similarity in results whereas the data collected during 2015 shows variation in all results. The Low weight and length or stunted growth is mainly because it breeds throughout the year which utilized great amount of energy for the development of gonadal products which in turn lowers the rate of feed conversion towards its growth. Another reason for the low weight of females is that they are maternal mouth brooder and during incubation of the eggs they can’t eat for several days. The diversity of fish catches from landing site Khambo at Keenjhar Lake comprised of both indigenous and introduced species representing a total of 21 fish species namely Mystus oar, Botia birdi, Wallago attu, Channa marulius, Mastacembalus armatus, Cirhinna spp, Chitala chitala, Cirhinna mirigala, Labeo rohita, Notopterus spp, Ciprinus carpio, Xenenthodon, Heteropneusteus spp, Catla catla, Mystus tengra, Mystus carasius, Heteropneusteus fossilus, Rita rita, Mastacembalus punctatus, Oreochromis mossambicu, and Oreochromis niloticus. During this study a total of 454680 fishes were landed with a total weight of 298231Kg.

In the present study the asymptotic length (L ) of O. mossambicus was 28.43 cm and growth rate (K) was 0.42 yr 1whereas, the asymptotic length (L ) of O. niloticus was

29.23 cm and growth rate (K) was 0.57 yr 1. The growth performance index in O. mossambicus ranged from 2.259 - 2.587 and in O. niloticus ranged from 2.398 - 2.67 in studied years. The natural mortality, fishing mortality was higher in in both species and shows increasing trend with a passage of time. The overall exploitation rate (E) was 0.7 in both species which is higher that E max. Smaller sized individuals of O. mossambicus and O. niloticus were rare in total catch. The absence of small size fishes in catch indicates the use of larger mesh size nets for fishing which facilitate the escape of small size fishes. The presence of higher number of carnivorous fishes in total catch indicates that fingerlings of both cichlids fishes might serve as a food for these abundant carnivorous and predatory fishes. In this lake heavy fishing is reflected xii

by the minimum number of large size specimens of both cichlid species. Factors such as availability of food, stress, pollution, seasons and environmental conditions might be a possible cause to affect the condition of fishes. In Keenjhar Lake the main sources of pollution are municipal and industrial effluents during flood seasons. The increase in catch as indicated through catch statistics and higher fishing mortality, appears to exert pressure in population of tilapia and other fishes in the lake. Control and management of fishing activities is strongly recommended.

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LIST OF TABELS Page No.

1. Monthly length-weight data of 7228 fishes of O. mossambicus from Keenjhar Lake during 2014. Length and weight parameters include minimum (Min), maximum (Max), mean and standard deviation (STD), total number (N) and slope value(b) calculated through Least Square method…….………………………....14

2. Monthly length-weight data of 7295 fishes of O. mossambicus during 2015. Length and weight parameters include minimum (Min), maximum (Max), mean and standard deviation (STD), total number (N) and slope value (b) calculated through Least Square method…...………………………………………...... 14

3. Monthly length-weight data of 7284 fishes of O. mossambicus during 2016. Length and weight parameters include minimum (Min), maximum (Max), mean and standard deviation (STD), total number(N) and slope value (b) calculated through Least Square method.……………………………………………..…..…15

4. Monthly length-weight data of 7303 fishes of O. niloticus during 2014.Length and weight parameters include minimum (Min), maximum (Max), mean and standard deviation (STD), total number (N) and slope value (b) calculated through Least Square method…….………..………………………………………………..…...16

5. Monthly length-weight data of 7305 fishes of O. niloticus during 2015. Length and weight parameters include minimum (Min), maximum (Max), mean and standard deviation (STD), total number (N) and slope value (b) calculated through Least Square method.……………………………………...……………….….…17

6. Monthly length-weight data of 7272 fishes of O. niloticus during 2016. Length and weight parameters include minimum (Min), maximum (Max), mean and standard deviation (STD), total number (N) and slope value (b) calculated through Least Square method………………………………………….……….…………17

7. Results of ANOVA………………………………………… ………………...…26

8. Total number of males and females of O. massambicus and O. niloticus at observed maturity stages………………………………………………………..43

9. Monthly variations in number of eggs in O. mossambicus and O. niloticus at maturity stage V during 2014-16………………………..………………...…….. 49

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10. Monthly variations in gonad length of male and female of O. mossambicus showing (Minimum, Maximum and Mean values) during 2014………..……….51

11. Monthly variations in gonad length of male and female of O. mossambicus showing (Minimum, Maximum and Mean values) during 2015……………...….52

12. Monthly variations in gonad length of male and female of O. mossambicus showing (Minimum, Maximum and Mean values) during 2016………………....52

13. Monthly variations in gonad length of male and female of O. niloticus showing (Minimum, Maximum and Mean values) during 2014……………..……...... 53

14. Monthly variations in gonad length of male and female of O. niloticus showing (Minimum, Maximum and Mean values) during 2015…….……………...…...... 53

15. Monthly variations in gonad length of male and female of O. niloticus showing (Minimum, Maximum and Mean values) during 2016……………………….….54

16. Monthly variations in DSI values in male and female of O. mossambicus during

2014-16…………………………………………..…………………………….…58

17. Monthly variations in values of DSI of male and female of O. niloticus during 2014-16………………………………………...…………………………………59

18. Scientific and local names of fishes of 21 species of fishes recorded at fish landing site Khambo at Keenjhar lake during 2014-16……….....……………...62

19. Weight (Kg) of each species caught per month at Khambo during 2014…...... 64

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20. Weight (Kg) of each species caught per month at Khambo during 2015……….65

21. Weight (Kg) of each species caught per month at Khambo during 2016…….…66

22. Total catch in numbers of 21 species caught at landing site Khambo during 2014…………………………………………………………………….……….69

23. Total catch in numbers of 21 species caught at landing site Khambo during 2015…………………………………………………………………………..….70

24. Total catch in numbers of 21 species caught at landing siteKhambo during 2016……………………….…………………………………………………….71

25.Calculated parameters for fishery status of O. mosambicus. L = asymptotic length; K= growth constant; GI = growth performance index; Z= total mortality; M= natural mortality; F= Fishing motality; E= exploitation rate; E max= maximum exploitation rate calculated through relative yield / recruit analysis…. 85

26.Calculated parameters for fishery status of O. niloticus. L = asymptotic length; K= growth constant; GI = growth performance index; Z= total mortality; M= natural mortality; F= Fishing motality; E= exploitation rate; E max = maximum exploitation rate calculated through relative yield / recruit analysis…..85

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LIST OF FIGURES Page No.

1. Map of study site showing Khambo at Keenjhar Lake……………...…….…..7

2. Length-weight relationship (LWR) of O. mossambicus during 2014. ..……..19

3. Length-weight relationship (LWR) of O. mossambicus during 2015………..20

4. Length-weight relationship (LWR) of O. mossambicus during 2016 ……….21

5. Length-weight relationship (LWR) of O. niloticus during 2014……………..22

6. Length-weight relationship (LWR) of O. niloticus during 2015……………..23

7. Length-weight relationship (LWR) of O. niloticus during 2016……………..24

8. PCA analysis based on length-weight relationship during 2014-2016……....25

9. Relative condition factor (Kn)of O. mossambicuss during (2014-2016)…...27

10. Relative condition factor (Kn)of O. niloticuss during (2014-2016)…………28

11. Length composition of both sexes of O.mossambicus during 2014-16……...29

12. Length composition of male of O.mossambicus during 2014-16…………...30

13. Length composition of female of O.mossambicus during 2014-16…………31

14. Length classes of both sexes of O. niloticus during 2014-16………………..32

15. Length composition of male of O. niloticus during 2014-16………………..33

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16. Length composition of female of O. niloticus during 2014-16……………...34

17. Weight composition of both sexes of O.mossambicus during 2014-16……..36

18. Weight composition of male of O.mossambicus during 2014-16…………...37

19. Weight composition of female of O.mossambicus during 2014-16…………38

20. Weight composition of both sexes of O. niloticus during 2014-16………….40

21. Weight composition of male of O. niloticus during 2014-16……………….41

22. Weight composition of female O. niloticus during 2014-16…………………42

23. Frequency of maturity stages of male of O. mossambicus during 2014-16……………………………………………………………………..44 24. Frequency of maturity stages of female of O.mossambicus during 2014-16………………………………………………………………….....45

25. Frequency of maturity stages of male of O. niloticus during (2014-16)…….47

26. Frequency of maturity stages of female of O. niloticus during (2014-16)….48

27. Length of ovary and testes of O. niloticus at maturity stage V……………...51

28. Monthly variations in Gonadosomatic Index (GSI) in male and female of O. mossambicus during 2014-16…….………………..……………………….55

29. Monthly Gonadosomatic Index (GSI) of O. niloticus male and female during 2014-16……………………….……………………………………..57

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30. Comparison between Gonadosomatic Index (GSI) and Digestosomatic Index (DSI) of O.mossambicus female during 2014-16…………………………..60

31. Comparison between Gonadosomatic Index (GSI) and Digestosomatic Index (DSI) of O .niloticus female during 2014-16………………………………..61

32. Monthly relative catch in numbers showing fishery status of O. mossambicus and O. niloticus during 2014………………………...... 73

33. Monthly relative catch in numbers showing fishery status of O. mossambicus and O. niloticus during 2015………………………...... 74

34. Monthly relative catch in numbers showing fishery status of O. mossambicus and O. niloticus during 2016………………………...... 75

35. Monthly variations in relative weight showing fishery status of O. mossambicus and O. niloticus during 2014…………………………….…….77

36. Monthly variations in relative weight showing fishery status of O. mossambicus and O. niloticus during 2015…………………………….…….78

37. Monthly variations in relative weight showing fishery status of O. mossambicus and O. niloticus during 2016…………………………….…….79

38. Growth performance index of O. mossambicus and O. niloticus…………….80

39. Virtual population analysis (VPA) of O. mossambicus showing estimated population and fishing mortality (Ft) / Year ………………………………...81

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40. Virtual population analysis (VPA) of O. niloticus showing estimated population and fishing mortality (Ft) / Year………………………...……….82 41. Virtual population analysis (VPA) of O. mossambicus and O. niloticus based on three years pooled data showing estimated population and fishing mortality (Ft) / Year …………………………………………………...……………….83 41.1. Relative yield-per-recruit model for O. mossambicus and O. niloticus……...86

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INTRODUCTION

1. Introduction

Fish is a very important healthy food as it provides more than one billion poor people with most of their daily animal protein, nutrients and micronutrients requirements that are essential to development and growth. Fish is used throughout the world because of its benefits for health (Milner,et al., 2003). More than 250 million people depends directly or indirectly on fisheries and aquaculture for their livelihoods (https://www.worldfishcenter.org/why-fish).

Fish is a very important healthy and nutritious food with high quality of animal protein (Jamin and Ayinla, 2003; Idah and Nwankwo, 2013). Fish meat contain about 16-20% protein which is comparatively higher when compare to milk(3.5 %), eggs (12 %), rice(6.6%) and wheat (Abowei and Tawari, 2011). It contains amino acid lysine which is now used as protein supplement and reported to have anticancer properties (Barlas, 1986). It is the most important food in the world. Collectively (marine + fresh water) it represents about 14% of all animal protein on a global basis, 50% in Asia and 30-80 % in the West Africa. Freshwater fishes contribute more than 6% of the global annual animal protein for humans (FAO, 2007). In Pakistan only 14 kg meat is available per person per year and the share of fish meat is only 2 kg/person/years (Eyo, 2001; Abolagba and Melle, 2008; Aberoumand, 2013). Fish meat can be converted into body tissues more efficiently than farmed animals. Its digestibility is high and ranges between 85-90% (Rudolf, 1971).

Presently, fishing remains the largest use of wildlife in the world. The reported annual capture of both wild fish and aquaculture in 2010 was 149 million tones (FAO, 2012).About 94% of all freshwater fisheries are in developing countries (FAO, 2007). Fish provide food for millions of people, and also contribute to the country’s economic wealth (World Fish Center, 2002).

The freshwater cichlid fish “Tilapia” introduced from Africa to many tropical, subtropical and temperate regions of the world during the second half of the twentieth century (Pillay, 1990). Tilapia belongs to Class Actinopterygii, Order Perciformes, Family Cichlidae(Cichlids), Subfamily Pseudocrenilabrinae and Genus Oreochromis.

This genus contain 30 species namely Oreochromisamphimelas, O. andersonii, O. angolensis, O. aureus, O. chungruruensis, O. esculentus, O. hunter, O. ismailiaensis, O. jipe, O. karomo, O. karongae, O. korogwe, O. lepidurus, O. leucostictus, O. lidole, O. macrochir, O. mortimeri, O. mweruensis, O. placidus, O. rukwaensis, O. saka, O. salinicola, O. schwebischi, O. shiranus, O. spilurus, O. squamipinnis, O. tanganicae, O. upembae, O. mossambicus and O. niloticus.

The culture of Nile tilapia (Oreochromis niloticus) and worldwide spread of Oreochromis mossambicus, started during the 1940s and 1950s.The spread of Nile tilapia largely occurred during the 1960s to 1980s. In Asia, the Nile tilapia spread from Japan to Thailand in 1965, and from Thailand to the Philippines. In American continent it spread from Africa to Brazil in 1971 and to the United States in 1974. In 1978 Nile tilapia was introduced to China, which now leading the world in tilapia production. China consistently producing more than half of the tilapia global production yearly.O. niloticus is one of the ten most important aquaculture species in the world (Picker and Grifths, 2011) which is now introduced into more than 90 countries around the world (Fitzsimmons, 2001). It is one of the most important species of fish which contributed in the reduction in the demand for protein (Romanol et.al., 2013). Its production worldwide increased from 1,099,268 tons in 1999 to approximately 3.500.000 tons in 2010 ( FAO, 2012).

O.niloticus and O.mossambicus are found in both freshwater as well as in brackish water. They live and grow in various naturally occurring freshwater bodies such as lakes, rivers and sewage canals and feeds throughout the water column i.e. bottom, mid water and surface(Bailey, 1994). They are potamodromous fishes as they show short migratory behavior for spawning purposes(Riede, 2004). These are mainly oviparous fishes consumes phytoplankton or benthic algae as a food (Breder, and Rosen, 1966). They exist in waters with temperature ranging from 14°C to 33°C (Philippart, and Ruwet, 1982). The size at first maturity varies usually from 6 to 28 cm but have capacity to gain much more size and weight (Eccles, 1992; IGFA, 2001). Maximum reported size and weight of O. niloticus is 60 cm and 4.3 kg. It has a long life span and can live up to 9 -7 years (Noakes, and Balon, 1982). Matures within 3 to 6 months. The maturity time depends upon the water temperature. O.

niloticus reproduces only when the water temperature is higher than 20°C (Trewavas, 1983). They are highly resistant to diseases and reproduces prolifically under natural conditions (Thomas, et.al., 2003)

In Asian tropical inland water mainly in reservoirs and lakes, exotic tilapias form important components to the capture fisheries. Two species of African tilapia species, Oreochromis mossambicus and O. niloticus have established productive populations in most lacustrine water bodies in tropical Asia. As a matter of fact, these two species undergo precocious sexual maturation under certain adverse conditions (Pullin, 1982). The growth and mortality of cichlid fish species such as O. mossambicus and O. niloticus reported to show spatial and temporal variations (Pullin and Lowe-McConnell, 1982; Amarasinghe, et.al., 1989).

Tilapia species got more popularity in aquaculture beside the carps (Daudpota, et.al., 2016; Kembenya, et.al.,2014; Malik, et.al., 2014 and presently they are one of the most farmed fish in the world ( World Bank, 2013). In recent years production of tilapia has increased day by day in different parts of the world (FAO, 2012).

Population dynamics of fish stocks are of importance for defining fishery management strategies. Since a wide array of length-based stock assessment methodologies is now available (Pauly and Morgan 1987, Sparre, et.al.,1989). It is possible to select appropriate techniques to assess exploited fish stocks in reservoir (Amarasinghe and De Silva, 1992). Several studies on the biological aspects and population dynamics of fishes in various parts of the world has been carried out such as (Chimits, 1955; Beverton and Holt,1959 ; Ucthida and King, 1962; Cridland, 1962; Chen, 1969; Swenson and Smith, 1973; Mishriji and Kubo, 1978; Lee, 1979; Pauly,1980; Hepher and Pruginin, 1981; Balarin and Haller, 1982; Philippart and Ruwet, 1982; Trewas, 1982; Roff, 1984; Jenson,1985; Macintosh, 1985; Pauly, 1986; Pandianand Varadraj, 1987; Payne, et.al.,1988; Boisclair and Leggett,1989; Little, 1989; Beverton,1992; Kwak, et.al., 1992; Charnoy, 1993; Christensen and Pauly, 1993; Macintosh and Little 1995; Jenson, 1996; Weliange, et.al., 2006).

In Pakistan two exotic species Oreochromis mossambicus and O. niloticus show wide range of expansion and prolific colonization in most freshwater and saline inland waters of Pakistan.

In Keenjhar Lake these two cichlid species form significant portions of the commercial landings. However, no studies have been done in past on the population dynamics and fishery status of these two species in Keenjhar Lake. It is necessary to investigate the population dynamics and biological characteristics of O. mossambicus and O. niloticus in inland waters of Pakistan for designing effective management strategies. The present study deals with the investigation of the present status of the cichlid fishery of Keenjhar Lake. Knowledge about the population dynamics of unfished populations of the two cichlid species might be useful for adopting management strategies in other reservoirs where these two species are dominant.

MATERIAL AND METHODS

Fisherman ready to throw net in lake.

2. Materials and Methods 2.1. Study site The data for this study were collected from Keenjhar Lake which is situated North- East of Thatta district and about 113 km from Karachi (Figure 1). The location of lake is 68 .03´E and 69ºNE and latitude 24º and 25ºN with temperature variation (25.5ºC – 37.8ºC) and maximum rain fall (17,98,50) July to September. Keenjhar is the largest freshwater reservoir in Sindh and provides the drinking water to Karachi. The Keenjhar Lake covers the area of about 24 kilometers. The Lake receives fresh water input from the Indus River. It is a Ramsar site and a Wildlife Sanctuary as the reservoir attracts a large population of migratory birds. The Keenjhar Lake is also a hot picnic point and a tourist attraction due to its historical importance. Kenjhar Lake receives flood water during southwest monsoon season through Haroolo Drain which brings contaminants in the reservoir. The lake also receives the domestic waste from surrounding villages.

Figure 1. Map of study site showing Khambo at Keenjhar Lake.

2.2. Data Collection The specimens and data were collected from the landing site Khambo twice in a month (1st day and 15th day) for three years (January 2014- December 2016).

2.3. Morphometrics

A total of 43200 specimens were examined during three year period. The total length (TL) of fish was measured to the nearest centimeter by using scale and weighed (TW) in grams by using digital balance (0.01- 5000 g) as described by Legler (1970).

2.3.1. Length-Weight Relationship For the study of Length-weight relationship (LWR) the collected length-weight data was transformed logarithmically. The Length-weight relationship (LWR) was estimated by using the least square method through equation:

Log W = log a + b x Log L and W = a Lb(Rricker, 1975) where, W = The weight of fish in grams L = The Total length of fish in centimeters a = The intercept of the regression curve b =The regression coefficient

2.3.2. Condition factor The condition factor of fish was calculated by using equation

Kn= W/ a Lb(LeCren, 1951) Where, Kn = Relative condition factor 8

W= Weight of fish in grams a = The intercept of the regression curve L = Total length of fish in centimeters b =The regression coefficient

2.4. Biological study For the biological 2880 mature specimens were collected and dissected during three years(2014-17), 40 specimens of each species O.mosambicus and O.niloticuswere collected monthly and transported to laboratory during the study period (2014- 2017). In laboratory, the length (cm) and weight(g)of fish was noted before dissection. After dissection the sex, maturity stage, gonad weight(g),gonad length(cm), number of eggs and stomach weight (g) were noted according to prescribed methods (Holden and Raitt, 1974). For the identification of maturity stages, the following six point macroscopic maturity scale (Kesteven, 1960) was used:

Stage I = Virgin / Rest: gonads pale in colour, occupying a small part of the body cavity. Stage II = Early maturing: testes and ovaries translucent, slightly larger in size. Stage III = Developing: testes and ovary opaque, increase in weight and volume. Stage IV = Developed: testes reddish white. Ovary orange-red, eggs spherical. Stage V= Spawning/gravid: testes white and flabby. Ovary transparent, occupying almost entire body cavity, riped eggs visible. Stage VI = Spent: testes and ovary shrunken, walls loose, only few eggs left in ovary.

After the determination of maturity stage, the gonads were taken out from fish on the measuring scale to measure the gonad length (cm) and weight (g) by using digital balance.

2.4.1. Fecundity Only ovaries of maturity stage (IV,V and VI) were preserved in Gilson’s fluid for 48 hours and periodically shaken which help loosen the ovary tissue and ensure the

penetration of preservative. After 48 hours preservation and vigorous shaking can completely liberated the eggs from the tissues. After this eggs spread on blotting paper to dry in air. Total number of eggs were weighed and random samples of about 100 eggs were counted out and weighed. The total number of eggs in the ovary was obtained from the equation:

F= nG / g

Where, F=fecundity, n=number of eggs in the subsample, G=total weight of the ovaries, g=weight of the subsample in the same units.

2.4.2. Gonadosomatic index (GSI) For the calculation of gonadosomatic index the fishes were dissected and the weight of gonads were noted in grams. The GSI was determined by using equation:

Gonadosomatic index (GSI)= (Wet weight of gonads/Wet body weight)x 100

2.4.3. Digestosomatic index(DSI) For the calculation of digestosomatic index the fishes were dissected and the weight of digestive tract was noted in grams. The DSI was determined by using equation:

Digestosomatic index (DSI)= (Wet weight of digestive tract/Wet body weight)x 100

2.5. Fishery status For the determination of fishery status the data was collected from the landing site Khambo at Keenjhar Lake. The landing data were collected from 20 boats per month for three years (January 2014-December 2016). Species diversity and their catch in

kilograms were recorded from each boat. The fishes were identified through the available literature (Qureshi,1965). 2.5.1. Growth performance and population estimation The growth performances of both O. mossambicuss and O. niloticus were calculated by using the length class frequency data by running ELEFAN I (Pauly and Morgan, 1987) and by Shephard’s method (Shephard, 1987) in FISAT II programme package to check the difference in K values. Only the results of ELEFAN 1 were used in this study. The K-scanning was used to identify the von Bertalanffy Growth Function (VBGF) and the mid lengths. The cut-off lengths were identified by plotting the pseudo-catch curve and were used to estimate the asymptotic length (L∞)by Powell- Wetherall method (Powell, 1979; Wetherall, 1986). The growth performance index

(ø') was calculated by the equation: ø'= log 10(K) + 2 log 10(L∞). Virtual population analysis was performed by using length class frequency data to reconstruct population and to estimate fishing mortality (Pauly 1984a).

2.5.2. Mortality rates The natural mortality rate(M) was calculated by the Pauly’s empirical equation (Pauly, 1980): M = -0.0152 – 0.279 Log L∞ + 0.6543 Log K + 0.463 Log T . Where, L∞ = asymptotic length in cm K = VBGF growth constant T = average habitat temperature which is 25.5 o C in present study.

The total mortality (Z) was calculated by the Beverton and Holt model (1956).

Z = K (L∞ - L mean) / (L mean – L’) Where, L∞ = asymptotic length in cm K = VBGF growth constant L mean = mean length of fish in cm L’ = cut-off length in cm

The fishing mortality F was calculated by subtracting the value of M from Z.

2.5.3. Exploitation ratio and stock assessment The exploitation ratio (E) was calculated by the equation E= F / Z. The relative yield per recruit was calculated through Beverton and Holt model (1966).

2.6. Statistical analysis Regression analysis One-way ANOVA and PCA was performed to test the length- weight relationship.

RESULTS

3. Results 3.1. Variations in length and weight 3.1.1.Variations in length and weight of O. mossambicus

During the year 2014 a total of 7228 specimens of O. mossambicus were measured. The total length(TL) ranged between 11 – 28 cm (Table 1). The minimum length of 11cm were observed during the whole year except January in which 12cm length was observed in fishes. The maximum TL (28 cm)in fisheswere observed during February to October. The weight (W) of O. mossambicusranged between 17- 425 g (Table 1). The minimum weight (17 g) was obtained during January and maximum weight(425 g) in June.

A total of 7295 specimens of O. mossambicus were studied during 2015. The TL ranged between 11 -28 cm (Table 2). The TL of 11cm were obtained throughout the year except June in which the minimum length of 12cm was obtained. The maximum length of 28 cm were observed during January, August, September, and November. The minimum weight (33g)was obtained during December while maximum weight of 430 gm was observed in August (Table 2).

A total of 7284 specimens of O. mossambicus were studied in 2016. The TL ranged between 11-28cm. The minimum size (11cm TL) of fishes were observed throughout the year except in July, September, October and December(Table 3). The maximum TL (28 cm) were observed during January, February and May. The minimum weight (35g)was obtained during January-April and the maximum weight (428 g) in May (Table 3).

The comparison of length-weight data indicates that the range of length in O. mossambicus remains same between the studied years in contrast to weight which shows increasing trend.

Table 1.Monthly length-weight data of 7228 fishes of O. mossambicus from Keenjhar Lake during 2014. Length and weight parameters include minimum (Min), maximum (Max), mean and standard deviation (STDV), total number (N) and slope value (b) calculated through Least Square method.

Table 2.Monthly length-weight data of 7295 fishes of O.mossambicus during 2015. Length and weight parameters include minimum (Min), maximum (Max), mean and standard deviation (STD), total number (N) and slope value (b) calculated through Least Square method.

Table 3.Monthly length-weight data of 7284 fishes of O. mossambicus during 2016. Length and weight parameters include minimum (Min), maximum (Max), mean and standard deviation (STD), total number (N) and slope value (b) calculated through Least Square method.

3.1.2.Variations in length and weight of O. niloticus

A total of 7303 specimens of O. niloticus were studied during 2014. The total length (TL) of O. niloticusranged between 11 – 28 cm (Table 4). The minimum TLof fishes were obtained during July to October and in December. The maximum length of fish (28 cm TL) was observed during January – March, May, and September -December. The weight in fishes during 2014 was ranged between 32- 430 g. The minimum weight (32g) was obtained in February and maximum (430 g) in October and November (Table 4).

A total of 7305 specimens of O. niloticus were studied during 2015. The total length (TL) ranged between 11 – 29 cm(Table 5). The minimum TL of fishes(11cm), was observed throughout the whole year except in January (13cm), March and April (12cm)in which comparatively larger fishes were caught. The maximum length of fish (29 cm TL) was observed during August-December. The minimum weight (40g) was observed throughout the whole year except in November (41 gm) and maximum weight (427 gm) in November (Table 5).

During 2016, the length and weight of 7272 specimens of O. niloticus were measured. The total length (TL) ranged between 11 – 29.5 cm (Table 6). The small size fishes of 11 cm were observed throughout the year in the samples collected from the landing site. The maximum length of fish (29.5 cm TL) was obtained during February. Minimum weight (27g)was obtained in August and maximum (430 gm) in April and August(Table 6).

Table 4.Monthly length-weight data of 7303 fishes of O. niloticus during 2014. Length and weight parameters include minimum (Min), maximum (Max), mean and standard deviation (STD), total number (N) and slope value (b) calculated through Least Square method.

Table 5.Monthly length-weight data of 7305 fishes of O. niloticus during 2015. Length and weight parameters include minimum (Min), maximum (Max), mean and standard deviation (STD), total number (N) and slope value (b) calculated through Least Square method.

Table 6. Monthly length-weight data of 7272 fishes of O. niloticus during 2016. Length and weight parameters include minimum (Min), maximum (Max), mean and standard deviation (STD), total number (N) and slope value (b) calculated through Least Square method.

3.1.3. Length-weight relationship (LWR)

The length-weight relationship for O. mossambicus is shown in Figures 2-4. In the present study, the length-weight relationship of O. mossambicus during three years (2014-2016) was determined by using logarithmic transformation. The figures showed the descriptive statistics and estimated parameters of LWRs (a and b) and the coefficient of determination (r²).

During 2014, the value of b in O. mossambicus ranged from 2.435 to 2.625 and r² value ranged from 0.716 to 0.823 (Figure 2). During 2015, (b) value ranged from 2.344 to 2.621 and r² was from 0.607 to 0.708 (Figure 3) and during 2016, b value ranged from 2.540 to 2.762 and r² value ranged from 0.569 to 0.751 (Figure 4).Overall the length-weight of O. mossambicus shows strong relationship.

The descriptive statistics and estimated parameters of LWRs (a and b) and values of the regression analysis (r²) for the O. niloticus are shown in Figures 5-7. During 2014, the value of b ranged from 2.49 to 2.868 and coefficient of determination (r²) value ranged from 0.622 to 0.733(Figure 5).During 2015, the value of b ranged from 2.461 to 2.975 and r² value ranged from 0.628 to 0.714 (Figure 6) and during 2016 (b) value ranged from 2.373 to 2.607 and r² value ranged from 0.666 to 0.816(Figure 7).

Figure 2. Length-weight relationship (LWR) of O. mossambicus during 2014.

Figure 3. Length-weight relationship (LWR) of O. mosambicus during 2015.

Figure 4. Length-weight relationship (LWR) of O. mosambicus during 2016.

Figure 5. Length-weight relationship (LWR) of O. niloticus during 2014.

Figure 6. Length-weight relationship (LWR) of O. niloticus during 2015.

Figure 7. Length-weight relationship (LWR) of O. niloticus during 2016.

3.1.4. STATISTICAL ANALYSIS The PCA of length and weight of O.mossambicus show strong relation with each other in 2014 and 2016 but not in 2015. PCA of O.niloticus show the same results. (Figure 8).During study years 2014-16 both species O. mossambicus and O. niloticus show significant (p<0.05) raise in body weight (Table 7).

Figure 8. PCA analysis based on length-weight relationship during 2014-2016.

Table 7. Results of one-way ANOVA at probability <0.05.

3.2. Condition factor (Kn)

Figure 9 and 10 shows the relative condition factor of O. mossambicus and O. niloticus. During the year 2014 the relative condition factor (Kn) of O. mossambicus ranged between 0.667 to 1.557. In 2015 Kn value ranged from 0.767 to 2.019 and in 2016 the Kn value ranged from 0.410 to 0.976 (Figure 9).

The relative condition factor (Kn) values for the O. niloticus during 2014 was 0.26 to 1.05. In 2015, the Kn value ranged from 0.18 to 1.13 and in 2016 it was 0.65 to 1.46 (Figure 10).

Figure 9.Relative condition factor (Kn)of O.mossambicuss during 2014-2016.

Figure 10.Relative condition factor (Kn) of O.niloticus during2014-2016.

3.3 Observation of gonads and length composition of O. mossambicus and O. niloticus

The length class data of O. mossambicus during study period 2014-2016 indicates that the fishes of both sexes in size class 17-18cm, 20-21cm and 18-19 cm were dominant respectively (Figure 11). The smallest matured fishes observed were of 13cm TL possess thread like, thin and semitransparent gonads. The gonads of >13cm TL size class were larger as compared to smaller size class. Distinguishable tissues of testicular and ovarian material was first observed in immature individuals of 13cmlength class.

Figure 11. Length composition of both sexes of O.mossambicus during 2014-16.

In 2014, the male specimens were dominant in 17-18 cm size class rather than the largest size class of 27-28cm (Figure 12).They possess the milky testicular structure. The female specimens were observed during this period show same trend as male but dominant females were larger as they belong to the size class (21-22cm) as compare to males (Figure 13). In 2015, the both males and females of size class 20-21cm were dominant as compare to the largest (27-28cm) and smallest (13-14cm) length classes (Figures 12 and 13). In 2016, the similar trend was observed for both males and females, but during this period the males were higher in length class 23-24cm(Figure 12) as compare to females which were more abundant in length class 18-19cm (Figure 13).

Figure 12. Length composition of males of O. mossambicus during 2014-2016.

Figure 13.Length composition of female of O. mossambicus during 2014-2016.

Figure 14-16 shows the length composition of O.niloticus during the study period 2014-16. Fishes of both sexes in size class 20-21cm were dominant (Figure 14). The smallest matured fishes observed were of 15cm TL having thread like, thin and semitransparent gonads. The gonads of >15cm TL size class were larger as compared to smaller size class. Distinguishable tissues of testicular and ovarian material were observed in individuals of 15cm TL, indicating immature stage length class.

During 2014, the male of two length classes (20-21cm and 23-24cm) were dominant (Figure 15). During 2015-16, both male and female fishes were dominant in larger size class (20-21cm) rather than the largest (27-28cm) and smallest (15-16cm)size class (Figures 15 and 16).

Figure 14. Length classes of both sexes of O. niloticus during 2014-2016.

Figure 15.Length composition of males of O.niloticus during 2014-2016.

Figure 16.Frequency of length classes of females of O.niloticus during 2014-16.

3.4. Observation of gonads and weight composition of O. mossambicus and O. niloticus

The weight composition of O. mossambicus during study period 2014-16 were shown in Figures 17-19. The fishes of both sexes of weight class (114-141g) and weight class (142-169g) were dominant (Figure17). The lightest matured fishes observed were of 59g possess thread like, thin and semitransparent gonads. The gonads of >59g fishes were larger as compared to lighter weight class. Distinguishable tissues of testicular and ovarian material first observed in immature individuals of 59g.

During 2014, the male specimens were dominant in heavier weight class 114-141g rather than the heaviest weight class of 444-471g and lightest class 59-86 g (Figure18). The males in this class possesses the milky testicular structure. Female specimens were observed during this period show similar trend (Figure19).

In 2015, both males and females of weight class (114-141g) were dominant and show the same trend as previous year (Figure 18 and 19). In 2016, trend was same as male and female of heavier classes were dominant than heaviest and lightest classes but during this period the males were dominant in weight class 279 - 306g (Figure 18) and were heavier as compare to female dominant weight class 142-169g (Figure 19).

Figure 17.Weight classes in both sexes of O. mossambicus during2014-16.

Figure 18.Frequency of weight classes in males of O. mossambicus during 2014-16

Figure 19.Weight classes in females of O.mossambicus during2014-2016.

The fishes of both sexes in O. niloticus during study period 2014-16 were dominant in weight class (143-171g), (199-227g) and weight class (227-225g) respectively (Figure 20). Overall the total number of fishes (217) of both sexes were higher in weight class 227-225g. The lightest matured fishes observed were of 59gpossess thread like, thin and semitransparent gonads. The gonads of >59gm fishes were larger as compared to lighter weight class. Distinguishable tissues of testicular and ovarian material first observed in individuals of 59g, both were immature stages.

During 2014, the male fishes were dominant in heavier weight class (143-171g) rather than the heaviest class (417-444g) and lightest class (59-86 g) with the milky testicular structure (Figure 21). Female specimens observed during this period showed similar trend (Figure 22).

In 2015, the male fishes of weight class (171 - 199 g) were dominant (Figure 21). Female specimens observed during this period were higher in weight class 199-227g (Figure 22). In 2016, the trend was same as male and female of heavier classes were dominant than heaviest and lightest classes. The higher number of both males and females were belong to the weight class of 227-255g (Figure 21 and 22).

During the study it was observed that the males of O. mossambicus were larger and heavier (23 – 24cm and 279 – 306 g; Figure 11 and 17) than the females (21-22cm and 142- 169 g; Figure 12 and 18). In contrast, the O. niloticus showed that the males were higher in length class of 23-24cm (Figure 14) whereas, females were higher in 20-21cm length class (Figure 15). Overall the total number of O. niloticus males (99 each) during three years was higher in weight class 199 – 227 g and 227-255 g and females (118) in 227 - 255 g.

Figure20.Weight composition in both sexes of O. niloticus during 2014-16.

Figure 21. Weight composition in males O. niloticus during 2014-16.

Figure 22. Weight composition in females of O. niloticus during 2014-16.

3.5. Monthly variation in maturity stages of O. mossambicus During three years study period a total of 1527 matured specimens of O.mossambicus were studied out of which 824 were females and 663 were males. The total number of females in IV maturity stage were 325, in V maturity stage were 324, inVI maturity 164 and 11 specimens were immature. Out of 663 males, 241 were at maturity stage IV, 289 were at maturity stage V, 111 were at the maturity stage VI and 22 were immature (Table 8).

During 2014 male of IV maturity stage were dominant in November, V maturity stage in April and VI maturity stage in February (Figure.23). During this period female of maturity stage IV were dominant in October, V maturity stage in September and VI maturity stage in January and March. (Figure 24). In 2015 male of IV maturity stage were dominant in September, V maturity stage in April and VI maturity stage in March, April, July and August (Figure 23), female of maturity stage IV were dominant in July and December, maturity stage V in August and VI maturity stage in April, July and October (Figure.24). During 2016 male of maturity stage IV were dominant in Jan, March, April, August and November, maturity stage V were dominant in December and maturity stage VI in April (Figure 23). Female during this period of maturity stage IV were dominant in July, V maturity stage in January to March, August, September; and female of VI maturity stage were dominant in May (Figure 24). Table 8. Total number of males and females of O. massambicus and O. niloticus at observed maturity stages.

Figure 23. Frequency of maturity stages in males of O. mossambicus during 2014-16.

Figure 24. Frequency of maturity stages in females of O. mossambicus during 2014-16.

3.6. Monthly variation in maturity stages of O. niloticus

During study a total of 1466 matured specimens of O. niloticus were studied. Out of these 753 were female and 713 were male. In females, 267 were at the maturity stage IV, 348 were at the maturity stage V and 137 specimens were at the maturity stage VI and 1 was immature. In males, 315 were at the maturity stage IV, 280 were at the maturity stage V and 117 specimens were at the maturity stage VI and 1 was immature (Figures 25 and 26).

During 2014 male of IV maturity stage were dominant in June, September and October, V maturity stage in March and July and VI maturity stage in December (Figure 25). During this period female of maturity stage IV were dominant in July, V maturity stage in February and VI maturity stage in January, July and November (Figure 26). In 2015 male of IV maturity stage were dominant in November, V maturity stage in July and VI maturity stage in March (Figure 25), female of maturity stage IV were dominant in June, September and December, maturity stage V in April and May and VI maturity stage in January to April (Figure 26). During 2016 male of maturity stage IV were dominant in April, maturity stage V were dominant in October and maturity stage VI in January and December (Figure25). Female during this period of maturity stage IV were dominant in December, V maturity stage in February, July and September, and female of VI maturity stage were dominant in June and July (Figure 26).

The female specimens of O. mossambicus and O. niloticus were observed fully matured at 21.37cm (TL). The maturity stages IV and V and fully ripe orange and reddish colour ovaries were recorded throughout the year except in March, October and November. Maturity stage VI or spent ovaries observed during the months of January to July, October and November.

Figure 25. Frequency of maturity stages in males of O. niloticus during 2014-16.

Figure 26. Frequency of maturity stages in females of O. niloticus during2014-16.

3.7. Fecundity Monthly variations in number of eggs at maturity stage V were noted. In 2014,O. mossambicus shows maximum number of eggs (4527) in June and lowest in February (Table 9). In the same duration O. niloticus show maximum number of eggs (8200) in February and lowest (1094) in May. In 2015, the maximum count of O. mossambicus eggs was obtained in August (8723), and in the same duration O. niloticus show maximum number of eggs (5984) in April. During 2016, the maximum numbers of O. mossambicus eggs (8417) were obtained in February, and in the same duration O. niloticus show maximum number of eggs (6070) in February.

Table 9. Monthly variations in number of eggs in O. mossambicus and O. niloticus at maturity stage V during 2014-16.

3.8. Morphology of the Gonads 3.8.1. Stage IV (Developed/Pre spawning) Ovary was enlarged occupying almost entire body cavity, with large number of big spherical ova of light orange colour. Testes was milky white with increased length and weight. 3.8.2. Stage V (Spawning) Ovarian wall become thin and transparent. Ripe ova were visible. Some eggs were present in oviduct. Testes were dull white in colour. 3.8.3. Stage VI (Spent) Gonads with loosed walls ovary contain few unspawned ripe eggs. Testes become shrinked with loose wall.

3.8.4. Gonad length in males and females During 2014 O. mossambicus gonad length in male ranged 0.8 – 10 cm and in female 1- 7.5 cm (Table 10). During 2015 O. mossambicus gonad length in male ranged 0.3 – 3 cm and in female 0.5- 4 cm (Table 11). During 2016 O. mossambicus gonad length in male ranged 0.3 – 5 cm and in female 0.2- 5 cm (Table 12). Gonad length of both sexes of O. niloticus were measured (Figure 27). During 2014 O. niloticus male show minimum gonad length of 0.2cm and maximum gonad length of5cm, the gonad length in female ranged between 0.2 to 7.5 cm (Table 13). The gonad length of O. niloticus during 2015 ranged between 0.3-5cm in male and 0.3 – 5.8 cm in female (Table 14). During 2016 O. niloticus gonad length in male ranged 0.3 – 4 cm and in female 0.2- 4 (Table 15).

Figure 27. Ovary and testes of O. niloticus at maturity stage V.

Table 10. Monthly variations in gonad length in male and female of O. mossambicus showing (Minimum, Maximum and Mean values) during 2014.

Table 11. Monthly variations in gonad length in male and female of O. mossambicus showing (Minimum, Maximum and Mean values) during 2015..

Table 12. Monthly variations in gonad length in male and female of O. mossambicus showing (Minimum, Maximum and Mean values) during 2016.

Table 13. Monthly variations in gonad length in male and female of O. niloticus showing (Minimum, Maximum and Mean values) during 2014.

Table 14. Monthly variations in gonad length in male and female of O. niloticus showing (Minimum, Maximum and Mean values) during 2015.

Table 15.Monthly variations in gonad length in males and females of O. niloticus showing (Minimum, Maximum and Mean values) during 2016.

3.8.5. GSI (Gonadosomatic Index) Monthly variations in GSI of both sexes of O. mossambicus and O. niloticus were given in figure 28 and 29.

During 2014 O. mossambicus males have lowest GSI (0.31) in February and December, and maximum (1.02) in June. In the same period females had minimum GSI (0.48) in July and maximum (1.39) in February. In males higher values of GSI were observed during April, June, July and November. In females higher values of GSI were observed during January, February and June.

In 2015, males possess minimum GSI (0.23) in May and maximum (0.42) in January. During this period female show minimum GSI (0.61) in January and maximum (1.29) in June. During 2015, the higher values of GSI in males were observed during

January, and February. In females the higher values of GSI were observed from March to October and in December.

During 2016, the males had minimum GSI (0.30) in January and maximum (0.83) in February. Female in this period showed minimum GSI (0.46) in May and maximum (1.28) in February (Figure 28). In males, the higher values of GSI were observed during February and December. In females, the higher values of GSI were observed from January to March.

Figure28.Monthly variations in Gonadosomatic Index (GSI) in males and females of O. mossambicus during 2014-16.

During 2014-16, the GSI index was calculated in males and females of O. niloticus. In 2014,the males have lowest GSI (0.25) in November and December, and maximum (0.62) in January. In the same period females had minimum GSI (0.44) in May and maximum (1.21) in October. Overall, the higher values of GSI in males were observed during January, February and August and in females the GSI values were high from September to March

In 2015, males possess minimum GSI (0.43) in January and June, and maximum (1.72) in March. During this period females show minimum GSI (0.55) in January and maximum (1.19) in August. During 2015, the higher values of GSI were observed during March, August to October and in December. In females, higher GSI were observed during April to December. During 2016, the males had minimum GSI (0.38) in June and maximum (0.74) in August. Females in this period showed minimum GSI (0.52) in July and maximum (1.20) in January (Figure 29).During 2016, in the higher GSI values in males were observed during August and September, and from January to May and in November and December in females (Figure 29).

Comparison of GSI values in O. mossambicus and O. niloticus shows that females of both species acquired higher values of GSI than males. The data indicates that O. niloticus preferably spawn in winter whereas, O. mossambicus spawn from January to September.

Figure 29. Monthly Gonadosomatic Index (GSI) in males and females of O. niloticus during 2014-16.

3.9. DSI (Digestosomatic Index) Monthly variations in DSI of both sexes of O. mossambicus and O. niloticus were given in Table 16 and 17. During 2014, the males of O. mossambicus had lowest DSI (1.98) in August and maximum (4.05) in March. In the same period females had minimum DSI (1.99) in

July and maximum (4.81) in January. In 2015, males possess minimum DSI(1.5) in August and maximum (3.46) in January . During this period females showed minimum DSI (1.26) in August and maximum (2.81) in May. During study in 2016 male had minimum DSI (1.92) in December and maximum (5.46) in May. Female in this period showed minimum DSI(0.75) in January and maximum (5.03) in May(Table 16).

During 2014-16both sexes of O. niloticus were studied, in 2014male have lowest DSI (0.52) in October and maximum (2.05) in April. In the same period female had minimum DSI (0.51) in October and maximum (1.56) in March. In 2015 the males possess minimum DSI (0.37) in December, and maximum (1.28) in May. During this period female show minimum DSI (0.50) in December and maximum (0.86) in July. During study in 2016 male had minimum DSI (0.45) in October and maximum (1.58) in December. Female in this period showed minimum DSI (0.35) in September and maximum (1.76) in April (Table 17).

Table 16. Monthly variations in DSI values in males and females of O. mossambicus during 2014-16.

Months Males Females 2014 2015 2016 2014 2015 2016 JAN 3.04 3.46 1.92 4.81 2.18 0.75 FEB 3.87 2.52 4.23 4.17 2.14 2.17 MAR 4.05 2.20 2.45 3.72 2.22 2.23 APR 3.17 2.01 2.25 3.15 2.72 1.91 MAY 2.80 2.72 5.46 2.67 2.81 5.03 JUN 3.18 2.66 4.00 3.74 2.63 3.24 JUL 3.06 2.61 4.32 1.99 1.82 3.45 AUG 1.98 1.50 2.90 2.91 1.26 2.10 SEP 2.99 1.83 1.50 2.91 1.64 0.84 OCT 2.37 2.53 2.03 2.18 1.84 1.47 NOV 3.14 1.95 1.77 3.20 1.41 1.35 DEC 2.32 1.77 1.26 2.28 1.65 1.11

Table 17. Monthly variations in values of DSI of male and female of O. niloticus during 2014-16.

Males Females Months 2014 2015 2016 2014 2015 2016 JAN 1.53 1.11 1.15 0.74 0.70 0.77 FEB 1.41 0.93 0.62 0.80 0.81 0.58 MAR 1.95 1.22 0.71 1.56 0.52 0.59 APR 2.05 0.72 0.87 1.30 0.73 1.76 MAY 1.66 1.28 0.79 1.12 0.63 0.92 JUN 1.81 0.56 0.58 1.31 0.51 0.71 JUL 1.31 0.69 0.61 1.35 0.86 0.71 AUG 1.87 0.78 0.48 1.27 0.70 0.98 SEP 1.19 0.79 0.54 0.72 0.67 0.35 OCT 0.52 1.08 0.45 0.51 0.57 0.62 NOV 1.72 0.81 0.70 0.98 0.64 0.60 DEC 1.47 0.37 1.58 1.05 0.50 0.68

3.10. Relation between GSI and DSI A comparison of GSI and DSI was given in (Figure 30 and 31). The GSI and DSI of both sexes of O. mossambicus show that when the GSI values increase the DSI values decrease (Figure 30). The GSI and DSI in O. niloticus also show the similar trend (Figure 31).

Figure 30. Comparison between Gonadosomatic Index (GSI) and Digestosomatic Index (DSI) of O. mossambicus females during 2014-16.

Figure 31. Comparision between Gonadosomatic Index(GSI) and Digestosomatic Index (DSI) of O. niloticus female during 2014-16.

3.11. CATCH COMPOSITION AND FISHERY STATUS The diversity of caught fish from landing site Khambo at Keenjhar lake comprised of both indigenous and introduced species. A total of 21 fish species namely Mystus oar, Botia birdi,Wallago attu,Channa marulius,Mastacembalus armatus,Cirhinna spp,Chitala chitala,Cirhinna mirigala,Labeo rohita,Notopterus spp,Ciprinus carpio,Xenenthodon,Heteropneusteus spp,Catla catla,Mystus tengra,Mystus carasius,Heteropneusteus fossilus,Rita rita,Mastacembalus punctatus,Oreochromis mossambicus, and Oreochromis niloticuswere recorded(Table 18)during study period and a total 454680 fishes were caught with a total weight of 298231Kg.

Table 18. Scientific and local names of 21 species of fishes recorded at fish landing site Khambo at Keenjhar lake during 2014-16.

3.11.1. Monthly variations in weight of 21 species in total catch landed at Khambo

The catch data during the three year study period showed monthly variations in the weights of 21. In 2014, the total catch of 105371Kg was recorded (Table 19). The highest catch was recorded in February (9518 Kg) and lowest in June (7203 Kg).The weight of Xenenthodon sppin the monthlytotal catch was lowest throughout the year except for January in which the lowest weight belongs to Oreochromis niloticus (86 Kg) (Table 19). Overall, Channa marulius, Wallago attu, Botia birdi, Mastacembalus armatus, Chitala chitala, Mystus oar showed highest weights in monthly total catch during 2014. The annual total catch in 2014 indicates that the total weight of Mastacembalus armatus was highest (8893 Kg) and Xenenthodon sppwas lowest (548 Kg) in the total catch landed at Khambo in 2014.

In 2015,the total catch was 94324Kg. The highest catch was recorded in February (10249Kg) and lowest in April (6132 Kg). The weight Xenenthodon was lowest in the total catch throughout the year except in January, May and September. In January lowest weight was recorded for Oreochromis niloticus (180Kg) and highest weight was (957Kg) of Channa marulius. The highest weight of Wallago attuwas recorded in February, March and December (1205, 850 and 663 Kg). In April and MayLabeo rohitawas highest in weight (443 and 593 Kg).In June and July the weight of Botia birdi(481Kg) and Mystus oar(556Kg) was high in the total catch. In August, September and October the weight of Heteropneusteusspp(540Kg),Chitala chitala(633Kg), of Channa marulius(770Kg) was high (Table20). Overall, the weight of Wallago attuwas highest (67495.5 Kg) and Xenenthodon spp was lowest (1004 Kg) in the total catch landed at Khambo in 2015.

In 2016 the total catch of 98536 Kg was landed. The highest catch was recorded in February (9244Kg) and lowest in November (7213kg).The weight of Xenenthodon and Notopterus spp was lowest in the monthly total catch throughout the year except for December in which the weight of Mystus tengra (48Kg) was lowest (Table 21). Chitala chitala, Catla catla, Labeo rohita, Mastacembalus punctatus, Ciprinus

carpio, Rita rita, and Oreochromis mossambicus showed highest weights in monthly total catch during 2014. Overall, the weight of Catla catla was highest (6785 Kg) followed by Labeo rohita (6768 Kg), whereas, the weight of Xenenthodon spp was lowest (940 Kg) in the total catch landed at Khambo in 2016 (Table 21).

3.11.2. Monthly variations in number of individuals of 21 species in total catch

A total of 454680 fishes belongs to 21 species were caught during the study period 2014-16. In 2014, total 133306 fishes were caught(Table 22). The highest number of fishes in catch was recorded in February (12944) and lowest in June (9544). From January to April the catch of Mystus oar was lowest (157, 154, 99,90 respectively). In May the lowest number of individuals (161) belonged to Notopterus spp. From June to November the lowest individuals of Xenenthodon spp was recorded and in December the count of Labeo rohita (259) was low. In January, April and May the individuals of Oreochromis mossambicus was highest (1092, 943, 919 respectively) in the total catch during 2014. Wallago attu showed its high abundance in March (1115), June (720) and July (888). The highest individuals (1299 fishes) of Cirhinna spp were caught in February. In August and September the highest number (1120 and 1041) of Mystus oar was recorded. Oreochromis niloticus was highest (1152 and 1354) in the total catch in October and in December (Table 22). Overall, the number of individuals of Oreochromis mossambicus was highest (10672 individuals)in the total catch landed at Khambo in 2014. The lowest number (2496 individuals) of Xenenthodon spp was landed during 2014.

In 2015, a total of 150184 fishes were caught (Table 23).Variations in fish catch were observed between months. The highest catch was recorded in February (14562) and lowest in April (10057). The numbers of Rita rita (447), Mystus oar (313), Ciprinus carpio (229) were low in the monthly catch of January, February and March. During April to August, the Notopterus spp, Catla catla, Wallago attu, Xenenthodon spp and Ciprinus carpio were low in numbers in the monthly catch respectively. The catch of Xenenthodon spp was lowest (170, 249 and 225 respectively) from October to

December. The catch of Oreochromis mossambicus was highest throughout the year except inFebruary, April and December. The Wallago attu was abundant (1373) in the catch of February, whereas, Oreochromis niloticus (831) and Mystus carasius (831) were high in numbers in the monthly catch of April and December (Table 23).

In 2016, a total of 171190 fishes belong to 21 species were caught. The highest catch was recorded in September (16841 individuals) and lowest in November (11876 individuals). The Xenenthodon spp was lowest in numbers in the monthly catches of January, February and August to November. Low numbers of Notopterus spp (301 individuals), Botia birdi (354individuals), and Mystus tengra (411individuals) were landed in March, April and in December respectively (Table 24).The catch of Oreochromis mossambicus was highest in the monthly catch landings throughout the year.

3.12. Variations in relative abundance of O. mossambicus and O. niloticus in total catch

A total of 454680 fishes were landed during three year study period at the landing site Khambo, out of which 44839 fishes belongs to O. mossambicus and 35731were of O. niloticus.

In 2014, 10672 individuals of O. mossambicus and 9045O.niloticuswere present in total the catch. The relative catch of O. mossambicus was highest (10 %) in January and lowest (5 %) in June. O. niloticus showed high relative catch in December (11 % ) and low (4 %) in January, February and August (Figure 32). The highest relative abundance of both tilapia species in the total catch was noted in December (18 % ).

In 2015,a total of 11898 fishes of O. mossambicus and 10144 O. niloticus were present in the total catch. The relative catch of O. mossambicus was highest (10 %) in January and lowest (6 %) in April whereas, O. niloticus showed high relative catch in April and May (8 % ) and lowest (4 %) in February (Figure 33). The highest relative abundance of both tilapia species in the total catch was noted in May (17 % ).

In 2016, a total of 22269 fishes of O. mossambicus and 16542 individuals of O. niloticus were present in the total catch. The relative catch of O. mossambicus was higher (15 and 16 %) in December and March and lowest (11 %) in January, February and July (Figures 34).O. niloticus showed high relative catch in April (12 % ) and low (7 %) in November and December. The highest relative abundance in catch of both tilapia species was noted in March (27 % ).

Overall the relative percentage of O.mossambicus and O.niloticus in the total catch in 2014-2016 ranged between 5-16 % and 4-12 % respectively. The comparison of early catch data indicates that the catch of O. mossambicus and O. niloticus increased from 2014-16 and that the O. mossambicus was more abundant in catch than O. niloticus.

Figure 32. Monthly relative catch in numbers showing fishery status of O. mossambicus and O. niloticus during 2014.

Figure 33. Monthly relative catch in numbers showing fishery status of O. mossambicus and O. niloticus during 2015.

Figure 34. Monthly relative catch in numbers showing fishery status of O. mossambicus and O. niloticus during 2016.

3.13. Variations in relative weight of O. mossambicus and O. niloticus in total catch

A total of 298231 kilogram catch landed at Khambo during the study period 2014- 16and out of which12476Kgwas of O. mossambicus and O. niloticus was 9148Kg. Both cichlids species contribute little in the total weight of fish landed at Khambo.

In 2014, a total 105301 Kg fish was landed in which O. mossambicus contribute 3449 Kg and O. niloticus represent 2603 Kg. The relative weight of O. mossambicus in catch was highest (4 %) in December and lowest (1 %) in January(Figure 35).O.niloticus showed high relative catch in weight in January (5 %) and lowest (2 %) in July and December. The both tilapia species collectively represented 4-7 % of the total weight of catch landed in 2014.

In 2015, a total of 94324 kilogram fish was landed in which O.mossambicus contributed 3193Kg and O. niloticus 2288Kg. The relative weight of O. mossambicus in catch ranged between 1-3 % and 2-4 % for O. niloticus (Figure 36). Both tilapia species contributed 3-7 %in the total weight of fish landed in 2015.

In 2016, 98536Kg of fish landed at Khambo in which O. mossambicus contributed 5834Kg and O. niloticus 4257Kg. The relative weight of O. mossambicus in catch ranged between 3-6 % with the highest in April (6 %). The relative weight of O. niloticus in total landings ranged between 5-7 % throughout 2016 (Figure 37), and the highest catch in terms of weight was recorded in August and December. Both tilapia species collectively represented 9-12 % of the total weight of catch landed in 2016.

Comparison of relative weights of O. mossambicus and O. niloticus with other fish showed that the representation of both cichlids in total landings were increased in 2016.

Figure 35. Monthly variations in relative weight showing fishery status of O. mossambicus and O. niloticus during 2014.

Figure 36. Monthly variations in relative weight and fishery status of O. mossambicus and O. niloticus during 2015.

Figure 37. Monthly variations in relative weight and fishery status of O. mossambicus and O. niloticus during 2016.

3.14. Growth performance and population estimation

The asymptotic length (L ) and growth rate (K) of O. mossambicus and O. niloticus during 2014-16 was shown in Figure 38. The asymptotic length (L ) of O. mossambicus was 28.43 cm and growth rate (K) was 0.42 yr 1whereas, the asymptotic length (L ) of O. niloticus was 29.23 cm and growth rate (K) was 0.57 yr 1(Figure

38).

Figure 38. Growth performance index of O. mossambicus and O. niloticus

The virtual population analysis (VPA) of O. mossambicus and O. niloticus indicates that the population is dominated by small sized fishes and the fishing mortality of length class > 17 cm TL was higher (Figure 39 to 41). The growth performance index in O. mossambicus ranged from 2.259 - 2.587. The growth index was low in 2016. The growth performance index in O. niloticus ranged from 2.398 - 2.67 and the growth index was also low in 2016 (Table 25 and 26)

Figure 39. Virtual population analysis (VPA) of O. mossambicus showing estimated population and fishing mortality (Ft) / Year

Figure 40.Virtual population analysis (VPA) of O. niloticus showing estimated population and fishing mortality (Ft) / Year.

Figure 41. Virtual population analysis (VPA) of O. mossambicus and O. niloticus based on three years pooled data showing estimated population and fishing mortality (Ft) / Year

The total mortality (Z) was calculated by the Beverton and Holt model. In O. mossambicus the total mortality was 3.293 yr -1 in 2014 and 4.039 yr -1 in 2016 (Table 25) while in O. niloticus the total mortality was 1.711 yr -1 in 2014 and 3.919 yr -1 in 2015 (Table 26). The natural mortality rate (M) was calculated by the Pauly’s empirical equation. In O. mossambicus the M was 1.0097 yr -1 in 2015 and 1.148 yr -1 in 2016. In O. niloticus the M was 0.7011 yr -1 in 2016 and 0.925 yr -1 in 2014 (Table 25 and 26) during the 2014-16. Fishing mortality (F) in both O. mossambicus and O. niloticus showed increasing trend (Table 25 and 26). The fishing mortality, natural mortality and total mortatlity of O. mossambicus was highest in 2016 ( 2.89) whereas, the mortalities of O. niloticus were high in 2015.

The exploitation rate with reference to F in studied years was 0.66 - 0.72 with overall exploitation rate of 0.7. The exploitation rates of O. mossambicus calculated through relative yield / recruit analysis at E0.5 for all three years was 0.33 whereas, the relative biomass per recruit was 0.307 (Figure 41.1). The value of E was slightly higher than the value of E max (0.656).

The exploitation rate was reference to F in studied years was 0.45 - 0.76 with overall exploitation rate of 0.77. The exploitation rates of O. niloticus calculated through relative yield / recruit analysis indicates the at E 0.5 for all three years was 0.326 whereas, the relative biomass per recruit was 0.296. The value of E was higher than the value of E max (0.584).

Table 25. Calculated parameters for fishery status of O. mosambicus. L = asymptotic length; K= growth constant; GI = growth performance index; Z= total mortality yr -1; M= natural mortality yr -1; F= Fishing mortality yr -1; E= exploitation rate yr -1; E max = maximum exploitation rate calculated through relative yield / recruit analysis.

Table 26. Calculated parameters for fishery status of O. niloticus. L = asymptotic length; K= growth constant; GI = growth performance index; Z= total mortality; M= natural mortality; F= Fishing mortality; E= exploitation rate; E max = maximum exploitation rate calculated through relative yield / recruit analysis.

Figure 41.1. Relative yield-per-recruit model for O. mossambicus and O. niloticus.

Discussion

Fishing boats at Keenjhar Lake

4. Discussion

Keenjhar lake is one of the largest freshwater lakes in Pakistan. Keenjhar Lake was declared Wildlife Sanctuary in 1977 under the Sindh Wildlife Protection Ordinance, 1972. It is a Ramsar site and also known as Kalri Lake. Previously many studies were carried out at Keenjhar lake such as vertebrate biodiversity, seasonal and environmental changes and their effects (Khan et.al., 2017), pollution (Yahya, et.al.,2016; Aziz, et.al.,2013a), but little information is available on the fish diversity in Keenjhar lake (Narejo, et.al.,2016).

Length-weight relation of O. mossambicus and O. niloticus from Keenjhar lake

In the present study during 2014-16, the total length (TL) and weight of both sexes of O. mossambicus ranged between 11cm - 28cm and 17g-471g. The observed length is less than maximum reported length of 29 cm (Naik,1973). Bano, et.al., 2012 reported 38.8cm TL with 842.5g weight in O. mossambicus from Malir River which is comparatively higher than the present observed TL. The present estimates of TL is greater than the reported TL of 26cm and weight of 295g from Manchar lake (Achakzai, et.al., 2013). During the same study period the observed length in O. niloticus ranged between 11cm- 29.5cm and weight 27-430g which is greater than the reported length (27.4cm) and weight (378.79g) from Baghdad (Attee, et.al.,2017) but lower than the reported length (44.5cm) from India (Mayank and Dwivedi, 2016). In the present study the change in weight is greater than the change in length which is in agreement with the earlier reports indicating greater change in fish weight as compare to length (Ahmed, et.al., 2011).

The mean value of regression coefficient (b) of O. mossambicus in present study was 2.7 which is closer to 2.93 as reported by (Naeem, et.al.,2011b). The b value in O. niloticus was 2.975 which is greater than 2.844 reported from Bangladesh (Ahmed, et.al.,2003). In the present study the value of b in both species is less than 3 indicating the negative allometric growth. The value of coefficient of correlation r²

for O. mossambicus and O. niloticus is 0.823 and 0.816 respectively. Mahmoud, et.al., 2013 and Mehak, et.al.,2017 reported value of r² of 0.9844 and 0.939 from Chashma barrage.

The relative condition factor (Kn) of O. mossambicus is 2.019 which is greater than the reported Kn value of 1.07 (Achakzai, et.al.,2013) but less than reported Kn value of 2.23 (Rizvi, et.al.,2009). The relative condition factor of O. niloticus was 1.46 which is less than 2.05 reported from Egypt (Mahmood, et.al.,2013) and also less than the reported value of 2.67 (Attee, et.al.,2017). A number of factors (e.g. food, stress, sex, pollution, season and environmental conditions) affect the condition of fishes. In Keenjhar lake the main sources of pollution are municipal effluent, industrial waste and raw sewerage (Yahya, et.al.,2016).

The phenomenon of dwarfing and stunting is well known and a major problem in tilapia culture (Fryer and Iles, 1969; Lorenzen, 2000). The low weight and length or stunted growth is mainly because it breed throughout the year, and all the energy is utilized for the development of gonadal products; therefore, the rate of feed conversion towards its growth is very low. Another reason for the low weight of female is that tilapia females are maternal mouth brooder and during incubating the eggs they cannot take food.

Variations in maturity, fecundity and spawning seasons In O. mossambicus results shows that there were more females at gonadal maturation stages throughout the year than males. Mature and active males were abundant in the months of April, July to September, November and December. Females had a high percentage of mature, active and ripe stages between the months of January, February, July to October. Difference in the peak spawning months in between male and female might be the possible cause of low production. The peak spawning occurred during July-September when both sexes show peaks in matured stages. The reported breeding season from India is from March to October (Hatikakoty and Biswas, 2002). This implies that fishing activities need to be minimal in this period.

In O. niloticus results show that there were more females at gonadal maturation stages throughout the year than males. The active, mature and ripe males were found in the months of March, April, June, July, September, October and November. Female had a high percentage of mature active ripe stages between the months of February, April to July, September and December. The difference in the peak spawning months in between male and female were observed in this study and indicates that the peak breeding occurred during April-July and September when both sexes show peaks of ripeness. The sex ratio is almost 1:1 among males and females available for reproduction. GSI value of O. mossmbicus male is 1.02 and female is 1.39. These values are less than the reported values of 3.1065 and 4.1420 for males and females (Sadekarpawar and Parikh, 2013). The calculated GSI value of O. niloticus male and female was 1.72 and female 1.21 which is comparable to the reported GSI value 1.66 (Soltan, et.al., 2011). The O. niloticus show two peak recruitment in population per year. Similar observation of two recruitments reported from Sri Lanka (Amarasingh and Silva, 1992). Fishing activities need to be minimal in this period.

Temperature play important role in the hormonal control of reproduction in Tilapia (Aronson, 1951 and Hyder, 1972). Peak of sexual activity appeared to be linked to the increasing temperatures for latitudes greater than 20º (El Zarka, et.al., 1970; Trewavas, 1983). The location of our study lake is tropical with temperature variation between 20ºC – 37.8ºC and maximum rain fall (17,98,50) July to September. As the temperature begins to increase, dissolved oxygen levels decreases in the lake which also affects maturation and metabolism of the fish as reported from other regions (Fryer and Ille, 1972). This means that there is a double pressure on the fish one is reproduction and the other is physiological constraint placed on the metabolism of the fish due to less oxygen levels.

Growth performance and Fishery status The catch statistics collected during 2014-16 indicates higher catches in kilogramms of Mystus oar ,Wallago attu and Catla catla whereas, Mystus oar, O. mossambicus and Wallago attu were the most abundant species in terms of numbers.

In the present study smaller sized individuals of O. mossambicus and O. niloticus were rare in the total catch. This indicates the mesh size of gill net used for fishing in Keenjhar is correct and allows the escape of small size individuals. Wallago attu and Mystusspp are reported as carnivorous and predatory fishes (Babare, et.al., 2013; Rama, 2014) and their high abundance in catch indicates that these fishes might possibly feed on the fingerlings of both cichlids fishes. Heavy fishing pressure is reflected by a decline in the mean size of fish caught (Pauly, et.al., 1998). In this lake heavy fishing is reflected by the decline in number of large size fishes in both cichlid species with a passage of time.

The present estimates of asymptotic length (L∞) of 29.23 cm TL of O. niloticus falls within the published ranges from other regions. The highest L∞ of 64.6 cm TL was reported from Kenya (Getabu,1992), whereas the L∞ of 17.9 cm TL was reported from Mexico (Gómez-Márquez, 2008). The present estimates of asymptotic length (L ) of O. niloticus is less than the reported asymptotic length (L = 41.5cm and 38.06 cm) of O. niloticus (Montcho, et.al., 2017; Mahmoud, et.al., 2013). The present L∞ of O. niloticus is closer to the reported asymptotic length of L = 27.50cm (El-Sawy, 2006). The growth rate of O. niloticus in present study was 0.57 yr 1 which is greater than the reported values of K= 0.33, 0.35 and 0.52 (El-Haweet, 1991; Dache, 1994; El-Sawy, 2006). GI (ɵ) growth performance Index of O. niloticus was 2.68 which show low growth performance. This value is close to the reported value 2.7 from lake Toho (Montcho, et.al., 2015) but lower than the 3.31 which is reported from the Nayanza Gulf of lake Victoria Kenya (Njiru,et.al., 2006).

Fishing mortality (F), was estimated from combined data of three years (2014-16) of O. niloticus as 3.08 yr -1 which is greater than the reported fishing mortality 2.13yr-1 (Mayank and Dwivedi, 2016). Fishing mortality rates were higher than natural mortality rates which suggest a very intensive exploitation of O. mossambicus and O. niloticus in the Keenjhar lake. Population of both species, O. mossambicus and O. niloticus, in Keenjhar Lake was mortality dominated as indicated by the Z/K ratio of 1.69 and 2.23 which is >1. The obtained value of E (Exploitation rate ) for both species (E= 0.7) in this study was higher than E0.5= 0.33 and the value of E max in O. niloticus (0.584) in O. mossambicus (0.656). The obtained value of E also indicates

high fishing efforts thus confirming the present findings of overfishing due to high fishing efforts. The phenomena of flooding is another cause which degrade the quality of water in flooding months. The flood waters was reported to bring high amount of contaminants in the Keenjhar lake which also cause high mortality of fishes in past (SUPARCO, 2012). The results of the present study indicates the need of monitoring and management of fishing practice in the Keenjhar Lake to prevent the decline of fish population in future.

5. Conclusion

The main findings about both species O. mossambicus and O. niloticus in Keenjhar Lake are as follow: 1. Both species show negative allometric growth throughout study period 2014-16. Low growth is mainly because it breed throughout year, and all the energy is utilized for the development of gonadal products thus the rate of feed conversion towards its growth is very low. Another reason for the low weight of female is that they are maternal mouth brooder and during incubating the eggs they can’t eat for several days.

2. Both species O. mossambicus and O. niloticus spawns throughout the year but O. mossambicus prefer to spawn in summer and O. niloticus prefer to spawn in winter season. Difference in the peak spawning months in between male and female was noted. GSI values of both sexes of both species were low. DSI values of both sexes of both species were high.

3. The asymptotic length (L ) of O. mossambicus was 28.43 cm and growth rate (K)

was 0.42 yr 1whereas, the asymptotic length (L ) of O. niloticus was 29.23 cm and

growth rate (K) was 0.57 yr 1. The growth performance index in O. mossambicus ranged from 2.259 - 2.587. The growth performance index in O. niloticus ranged from 2.398 - 2.67. The growth performance index was low in 2016.

4. The natural mortality, fishing mortality were higher in in both species and shows increasing trend with a passage of time. Fishing mortality of length class > 17 cm TL was higher. The exploitation rate with reference to F in studied years was 0.66 - 0.72 with overall exploitation rate of 0.7 in both species. Smaller sized individuals of O. mossambicus and O. niloticus were rare in total catch. The absence of small size fishes in catch indicates use of larger mesh size nets for fishing which facilitate the escape of small size fishes. In this lake heavy fishing is reflected by the minimum number of largest specimens of both cichlid species in the total catch.

5. The sewage pollution, flood waters and high fishing efforts might possibly affecting the condition and population of fishes in Keenjhar Lake.

6. Future recommendations

 Fishing activities need to be minimal during peak spawning months.  Sewage waters must be treated and controlled by implementing laws.  Formation of the no-take zones in the Keenjhar Lake is strongly recommended.

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Appendix 1

Comparison of frequency of length classes of O.mossambicus

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Appendix 2

Comparison of frequency of length classes of O.niloticus

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