The species of Tilapia reported by various investigators as occurring in the Niger River drainage are reviewed and corrections noted. Four species are presently known from Kainji Lake, including T. galilaea. T. nilotica, T. zillii and T. dageti. Separation of very small T. galilaea and T. nilotica by dorsal spine counts appears to be possible in Kainji Lake, and some criteria for separating T. zillii and T. dageti are reviewed.
The relationship of length-weight for T. galilaea and of standard length-total length for T. galilaea and T, nilotica is described. Fry of T. galilaea and T. nilotica is described. Pry of T. galilaea and T. nilotica were found over shallow gently-sloping mud-and-debris bottoms7 particularly near village clothes-bashing sites. These were not accompanied by fry of T. zillii or T. dageti. Indirect evidence suggests most intense spawning of T. galilaea occurs during filling and full supply level of the lake, between October and February.
Observations of commercial catches indicate Tilapia have increased in the lake over the period 1971 to 1972. The Tilapia catch by various sampling methods was composed of at least 75% T. galilaea which is presently dominant among the Tilapia species in the lake.
Size selectivity of gillnets and castnets for T. galilaea show a progressive increase with increasing mesh size. Assuming the mean length at maturity of this species to be similar to Volta Lake, the minimum mesh size for protection of the stock to allow one spawning season, is greater than 3-inch stretched mesh.
Commercial harvest is largely by passive and active gillnetting, and castnetting. Management recommendations include the organization of a fisheries management agency, limitation of the number of fishing units, methods of restricting the use of small-mesh nets, and enforcing the prohibition against fish poisons.
