The current status of the in Lake Kainji

Item Type conference_item

Authors Olowosegun, O.M.; Omorinkoba, W.O.

Download date 28/09/2021 08:20:00

Link to Item http://hdl.handle.net/1834/37335 THE CURRENT STATUS OF THE GENUS HYDROCYNUS IN LAKE KAINJI Olowosegun, O. M. & Omorinkoba, W. 0 NIFFR, P.M. B. 6006, New Bussa, Niger State. Email: [email protected] Abstract. Over a period of a year, a study was carried out to determine the morphology of the Genus Hydrocvnus which comprises f carnivorous fishes known as Tiger fishes. Determination of the morphology was carried out using both quantitative (morphometric and meristic) characteristics and qualitative characters such as colour and shape of the fish. It was discovered that some of the species that were available in large numbers in the lake in past years have decreased in number. The paper looks into the possible reasons for the reductionofthese commercially importantspecies Introduction The diversity of fish species in any water body is attributed to favourable conditions. Fish populations also respond to factors such as over fishing, pollution and eutrophication abundance in the aquatic environment (Welcomme, 1999). Today, numerous fish stocks and species have declined in abundance and composition since their historical peaks, and some have even gone extinct while others are being threatened, leading to urgent calls for morestringent management and the establishment of protected areas (Roberts, 2003). High reliance on fishing, together with the depletion of large high value stocks, .results in the exploitation of a great variety of species and habitats by diverse fishing methods and large concentrations offishers (Welcomme,2001) When a pre -damming survey took place in rocky stretches of the cut off channel of River Niger at Kainji in 1966 (Motwani and Kanwai, 1970) the composition of catches showed that the Characid group was most often recorded, followed by Mormyridae, Mochokidae and Schilbeidae. Sampling with a fleet of gill nets revealed that Hydrocynus forskalii and were among the species regularly and frequently sampled (Lelek, 1968) According to Banks et al. (1965) and Motwani and Kanwai (1970), the Characidae formed an insignificant part of the fish population before the lake's formation. However, within 18 months of the closure of the dam, the characid population had expanded to such an extentthat the family comprised 14.6% by number of the total experimental gill net catch for 1969 (Lelek, 1972) and was second only to the Citharinidae in terms of the contribution tothe total weight of the catch. By 1970, the Characidae had overtaken the Citharinidae to become the largest component of the gill net catches in terms of both number and weight (Lelek, 1972). This situation remained the same through 1970to 1972.The greater part of the Characid catch from 1970 to 1972 was composed of two species, Hydrocynus forskalii (Cuvier) and baremose (Joannis) both of which were abundant in all parts of the lake. The reason for the success of Hydrocynus forskalii which is an entirely predatory species was associated with the abundance of clupeids on which the former feeds. Lelek (1972) observed that fish of the Characidae family were almost constantly increasing in number and weight and in the latest samples of 1971;they were the most important componentof gill netcatches. By 1976, Blake (1976) reported that the commercial fishery of Lake Kainji was dependent on the very numerous characids, particularly Hydrocynus forskalii. The family Characidae is represented by three genera and fifteen species. Most species of this family are numerous and they make up an important part of the commercial catch. The genus Hydrocynus (or tiger fishers) are known to be strictly itcthyophagous. All the fish belonging to this genus appreciably look similar and only an attentive examination makes it possible to differentiatethem. (Leveque, et aI, 1990) Theobjective of this study was to compile information on the morphological characteristics of the genusHydrocynus and to distinguish between two species of the genus: (Iineatus) and Hydrocynus forskalii through the analysis of morphometric and meristic features and otherpeculiarcharacteristics that make field identification easier. Methodology Fishsampling and analysis: The fishes used in the study were obtained from Lake Kainji and the RiverNigernear Kainji Dam. Visits were made twice weekly from the month of April 2005 to April, 2006, Fish caught by fishers were examined physically to pick out samples of Hydrocynus species. Thesamplewas later sorted by species using identification keys by Holden and Reed (1972) and Reedet al. (1967). Care was taken not to damage the scales and the fins. Samples of the fish were preservedin 10% formalin solution for future reference. Charactersused in the identification of the species 1.Morphometric measurements The measurements taken were aimed at comparing the body shape in different species, Morphometriccharacters defined in Leveque et al. (1990) were measured and recorded in centimetersto the nearest 0.01cm, and this was done using a pair of dividers, measuring board, meterruleand a rope. Standardlength: The distance from the anterior part of the snout (with the jaw closed) to the base of thecaudalfin. Headlength: This was measured, with the mouth closed, from the tip of the snout to the posterior edgeoftheopercula bone. Headwidth: This was measured with gill covers closed Eyediameter: This was taken (using a pair of dividers and a ruler) as the length of the orbit 2. ~eristic cou nts Thisincludedthe fin ray counts, scale counts and the number of teeth in the upper and lower jaws of thefish. Fin ray counts: All rays of the paired fins (pectoral and pelvic) and the unpaired fins (dorsal, anal andcaudal)were counted, including the smallest ones atthe lower end of the fin base. Scalecounts: I. Lateral line scale counts: This represents the number of pored scales in the lateral line. The count was taken from the scale in contact with the shoulder girdle to the structural caudal base,by moving the caudal fin from side to side ii. Scales above lateral line: These were counted from the origin of the dorsal fin, including the smallscales and counting downward but not including the lateral line scale. iii. Scales below lateral line: These were counted upward from the origin of the anal fin (including the small scales).

3.Qualitative characters Observationswere also made on the shape and colour of the fish, with particular attentiongiven totheadipose fin, Atotal of fifty five (55) fish samples were examined and identified and data were collected,

Results Table1summarises the results of the morphological characteristics of Hydrocynus forskalii of Lake Kainji.Mostof the fish species gotten were Hydrocynus brevis and Hydrocynus forskalii (as seen in Fig.1),no species of Hydrocynus vittatus (Iineatus) was obtained throughout the period of study. t:-= 4 ..jj'j:% "=: J Dis-C~ssion ;'. From the result it is evident that most of the morphological attributes of Hydrocynus forska/ii aqreewith'descriptions of previous authors where reports were available. These include the colour of the fish which was generally silvery white, adipose fin (grey) and caudal fins (orange and forked), eye size, the shape and size of the teeth, which is very developed and sharp, a series on each jaw. The body profile, in line-with the available descriptions, is s.lender,(when compared with the only other species (H. brevis) obtained in the course of the study. The number of scale rows below the lateral line is two (2), which is also in line with the available descriptions by previous authors. No sample of Hydrocynus vittatus was obtained throughout the period of study but samples offish identified as Hydrocynus brevis were obtained. According to Lelek 1972, Hydrocynus vittatus (Lineatus) (Bleeker) which was recorded from the pre- impounded River by Banks et al.(1965) and Motwani and Kanwai (1970) was reported to be common on the newly formed lake by Turner (1970). It is therefore of interest that Hydrocynus vittatus rare during the period, October, 1970 to September, 1972, whereas Hydrocynus brevis, which was not mentioned by Turner (1970) but was recorded by Lelek (1972) was common. Itis considered likely that Hydrocynus brevis was misidentified as Hydrocynus vittatus by Turner.

Summary/Remark Since no sample of Hydrocynus lineatus was obtained in Lake Kainji area throughout the period of study, the differences between the two species (H. vittatus (Iineatus) and H. forskalit) have not been properly ascertained yet, but the species Hydrocynus forskalii obtained conform to available descriptions on their morphology, and further strengthen the ease of their identification. The abundance of Hydrocynus forskalii in Lake Kainji resulted from the development of a large clupeid population (Lelek, 1968). Lewis (1974) had shown that 71% of its diet was formed by clupeid species. The total number of fish species obtained throughout the study (55) showed a decline in the availability of the Hydrocynus species in Lake Kainji. A possible reason could bea decline in the clupeid fishes on which the Hydrocynus feeds. Another reason could be over fishing of this fish species which is a major commercial fish in Kainji.

Percentage of Hydrocynus species obtained

'I' ~ .. forskal"'J" •-"--_._.,.brevis

Figure 1: Species Composition of Hydrocynus Catches Hydrocynus forskalii - 94.54% Hydrocynus brevis - 5.46%

,:=,. ;:<64:...'"--"",,,- ...1 .... $....: ...: ...5 __ :_=...... :...... :_::_:_: __ :_=__ iiiiiiiioO"",J 1. Morphological characteristics of Hydrocynus forskalii of Lake Kainji paredwith Leveque et al. (1990), Olaosebikan and Raji (1998) and Reed et al. (1967).

This study Leveque et al . Olaosebikan Reed et al (1967) (1990) and Raji (1998) 10 in the upper Teeth large, A sin gle row in each jaw jaw. 8 in the canine like, of large pointed teeth lower jaw separated by which are razor sharp wide gaps on both edges, spaced well apart and can be seen even when mouth o is closed

Marked with Marked Dark longitudinal stripes black lines along each row of scales Grey Grey Grey Grey

Less than 70% Well developed adipose of interorbital eyelid

Silvery white Silver plated Grey or olive green on the back, sides are silvery, dark longitudinal stripes along each row of scales above the lateral line 2 2

Long and Slender profile Long, slender slender Orange Bright red Bright red

Forked Deeply forked

•.w.:.tArl~nces ,J. W., Holden, M.J and McConnell R. H (1965) Fishery report in: The First report of the Kainji Biological research team. Liverpool, Ed E. White Blake, B. F (1976) Lake Kainji, : A summary of the changes within The fish population since the impoundment of the Niger in 1968. Department of Zoology, University of Reading. Harding, D. (1964) Hydroloqy and Fisheries in Lake Kariba. Verh. Internat. Verein. Limnol. 15: 139 149. Holden, M and Reed, W. (1972): West African freshwater Fish West African Nature Handbook, Longman, London, 68pp. A. (1968) Fish population of Kainji Lake, trends in their development And utilization. FAO of the UN. Rome 1972. Technical Paper. ,A. (1972) Technical report of the Kainji Lake Research Project to the Government of Nigeria. (FI: SF/NIR 24 Technical.report 2). Leveque, C., Paugy, D & Teugels G.G (Eds) 1990: Faune des poisons D'eaux douces et saumatres de l'Afrique de I'Quest. Vol. 1 MRAC, Tervuren & ORSTOM, Paris Collection Faune Tropicale, 28: 1 384pp Lewis, D. S. C. (1974b) The food and feeding habits of (Cuvier) and Hydrocynusbrevis (Gunther) in Lake Kainji, Nigeria. J. Fish. BioI. 6: 349-363. Lowe McConnell, R. H. (1965): Field Identification of Freshwater fishes likely to occur In the area above the Kainji dam on the River Niger. In the First Scientific Report of the Kainji Biological Research Team. Edited by E. White, Liverpool: pp 43 64. Motwani, M. P. & Kanwai, Y. (1970) Fishes and fisheries of the coffer Dammed right channel of the River Niger at Kainji. Kainji Lake studies, Vol. 1: 27 48. Olaosebikan B.D andAminu Raji (1998): Field Guide to Nigerian Freshwater Fishes Published by Federal College of Freshwater Fishes, New Bussa, Niger State. 106pp. Reed, W., Burchard, J., Hopson, A.J., Jennes, J & Yaro, I (1967): Fish and Fishes of Northern Nigeria. Ministry of Agriculture, Northern Nigeria, Gaskiya, Zaria. 226pp. Roberts, C. M (2003) Application of ecological criteria in selecting marine Reserves and developing reserve networks. EcologicalApplications. 13: S215 S228. Turner, J. L (1970). The fish population of the newly impounded Kainji Lake, FAO/UNDP technical report of the Kainji Lake Research Project to the government of Nigeria (FI: SF/NIR 24 Technical report 1). W~lcomme, R. L (1999)A review of a model for qualitative evaluation of Exploitation levels in multi species fisheries. Fisheries mgt and ecology.6: 1-19. Welcomme, R. L (2001) Inland fisheries: Ecology and mgt. Oxford (United Kingdom): Fishing News Books, pp 99 134.