Msuku, B.S.

Tanzania Fisheries Research Institute (TAFIRI), P.O. Box 475 Mwanza, Tanzania

Aspects of the population ecology of Oreochromis esculentus in Lake Malimbe, a Lake Victoria satellite lake

The hypothesis that micro-geographical isolation has resulted in characteristic changes in the population of Oreochromis esculentus in Lake Malimbe, when compared to the original population in Lake Victoria, was studied. Species composition, distribution, food, fecundity, demographic aspects such as sex ratios and length-weight relationships of O. esculentus were examined in contrast to the historical populations in Lakes Victoria and Kyoga. On average 66% of the fish catches in Lake Malimbe comprised of O. esculentus. Comparison of the condition factor and demographic characteristics indicated that the species was in a healthy condition. However, the presence of alien tilapiine species, O. niloticus and O. leucostictus, coupled with the deficiency of the diatom Aulacoseira spp, a preferred food for O. esculentus, due to the increasing eutrophic status of Lake Malimbe, makes the continued existence of O. esculentus in the lake precarious. If the lake is well managed it could possibly serve as a natural living museum for the conservation of O. esculentus and a source of restocking material of this species into the Lakes Victoria and Kyoga.