Oreochromis niloticus has become rare in Lake Ayame, presumably because of the competition with another species of tilapia, Sarotherodon melanotheron. Its breeding season, size and age at first sexual maturity, fecundity and egg size were studied between October 1994 and October 1996. The breeding season occurred during the period from January to September, with a peak between April-May and July. The fish matured in their first year at 10 months old, at a size range between 11.6 cm and 13.5 cm SL. They produced few (416 and 343 eggs for a 100 g female in 1995 and 1996, respectively) but large eggs (7.7-7.9 mg as a mean). Life history traits of O. niloticus in Lake Ayame are compared to those obtained for other populations in Côte d’Ivoire, and discussed in relation to the interspecific competition with S. melanotheron.