The reproductive biology of Oreochromis niloticus, O, aureus and their hybrids from Lake Edku was examined. Female and male sex ratio is 1:1.07 for Nile tilapia (O. niloticus), 1:1.20 for blue tilapia (O. aureus) and 1:1.37 for hybrids. Length at first sexual maturity is 9.4cm (TL) for males and 10.3 cm (TL) for females of O. niloticus. The corresponding values for males and females of O. aureus are 8.2 and 9.2 cm respectively, while for hybrids these values are 8.2 cm for males and 8.4 cm for females. The breeding season of Nile tilapia extended from April to September with a peak of gonadosomatic index (GSI) in May, whereas in case of blue tilapia and hybrids, it extended from February until November with a maximum value in May. For all fish groups, the fecundity showed curvilinear relationship to fish length, body weight and ovary weight, The present study revealed that blue tilapia and hybrids are markedly less fertile than Nile tilapia.