The reproductive biology of Brycinus nurse (Paugy 1986), Pisces:-characidae in asa reservoir, Ilorin, Nigeria

A total of 980 specimens of Brycinus nurse caught in Asa reservoir from November 1991 to October 1993 were examined for reproductive attributes. Female dominance was observed within the population, with a sex ratio of 1.0 male to 1.78 females. The fish spawns during the rainy season from March to August, with peak spawning in March, June and July, months coinciding with the onset of the rains and flooding. The Gonadosomatic Index (G.S.I) of the population ofB.nurse in Asa reservoir ranged between 0.02-29.25% with a mean of 6.43 varying with season, size offish, sex and stage of gonadal maturity. The absolute fecundity ranged between 1,720 - 68,700 eggs with a mean of 18,281 eggs while relative fecundity ranged from 19,933 to 849,453 eggs /kg with a mean of 345,000 eggs /kg of body weight. The fecundity increased with gonad weight, but showed no significant relationship with body size. Egg diameter ranged from 0.49 to 0.82 mm with a mean of 0.63 mm. The River Asa population of B.nurse had lower mean values of G.S.I, egg diameter, and relative fecundity but higher estimates of absolute fecundity than other populations, previously studied. These differences were thought to have emanated from differences in geographical location.