The breeding biology of Oreochromis niloticus linnaeus (pisces: cichlidae) in Opa reservior Ile-Ife, Nigeria

Sampling for the fish Oreochromis niloticus in Opa reservoir started in October 1997 until February 2000. The fishing methods employed for collecting the 1430 specimens were cast netting and gillnetting. Egg diameter varied between 2.12mm and 2.69mm with a mean of 2.47 ± 0.02. Female gonadosomatic index was 1.05 ± 0.01 (0.12 - 4.06, n = 637). The male gonadosomatic index was 0.39 ± 0.02 (0.03 - 1.67, n = 789). O. niloticus bred throughout the period of study. The species was a material mouth brooder with the female fish carrying eggs and alevins in the buccal cavities. The sex ratio of O. niloticus was approximately 1:1 in the reservoir. The fecundity of the species was between 73 eggs and 1810 eggs with a mean fecundity of 815 eggs. The relative fecundity was between 0.26 eggs and 26.82 eggs per gram body weight. The correlation coefficient between log. fecundity and log. standard length was r = 0.370 and tested statistically (tcal = 15.0>ttab = 2.617; df 637). Journal of Science and Technology Vol. 25(2) 2005: 1-8