Some Aspects of Reproductive Biology of Bagrus bajad (Forsskal, 1775) from Kangimi Reservoir, Kaduna State, Nigeria

Some aspects of the reproductive Biology of Bagrus bajad were investigated to determine egg diameter, gonadosomatic index and gonad maturity stages. A total of five hundred and twenty-three (523) fish were collected by purposive sampling from the fishermen's bycatch for 24 months. Mean values calculated were analyzed statistically using analysis of variance at 95 % confidence level (p≤0.05). Duncan’s Multiple Range Test (DMRT) was introduced to rank the means when the difference is significant. Egg size measured showed no significant (P>0.05) variation from 0.988±0.05mm to 0.813±0.06mm. The peak (4.643±0.27%) of the gonadosomatic index was in August and the least (0.401±0.04) value was recorded in February for males. In females, the value fluctuated from 6.414±0.60% (June) to 0.510±0.09% (February). The mean gonadosomatic index for females and combined sex in the rainy months was significantly higher than the dry months at P<0.05. Six gonad maturity stages were identified. Testes and ovaries that were not matured occurred almost throughout the sampling period. Matured gonads were observed more in the rainy months. The fish with higher body weight recorded higher ovary weight but the size of the egg did not differ significantly among fish with varying body ranges. This implies that eggs contain the same amount of food reserve, so also survival and hatchability. The breeding pattern of B. bajad is during the rainy season and the fish are seasonal breeders. Histological study of male and female gonads of the same species in the reservoir is recommended to complement the macroscopic investigation. The exploitation of B. bajad in the reservoir should be within the dry season in order not to deplete the fishery of brood stock. Keywords: Egg size, Gonadosomatic Index, Maturity stages