Aspects of the Lake Victoria fisheries with emphasis on Oreochromis niloticus and Alestes sadleri from the Nyanza Gulf

The biology of the fish stocks and their fishery in Lake Victoria are reviewed. The major fisheries started to decline long before the introduction of the Nile perch (Lates niloticus ), therefore it is questionable whether this predatory species is the sole cause of decline in the stocks of tilapia and anadromous fish. Length-frequency data covering the period July 1985 to April 1986 for Oreochromis niloticus and Alestes sadleri were obtained from five landing Kenyan beaches in Nyanza Gulf and Port Victoria. Growth parameters were estimated for both species, and an estimate of total mortality was provided for A. sadleri . Fecundity of A. sadleri was found to be relatively low. Egg size increases with increasing gonad weight, fork length and total body weight, but the ratio of number of eggs and total body weight does not appear to change. Mean relative fecundity was 350 eggs/g body weight.