Breeding period and Fecundity of Tilapia nilotica L. in Lake Zwai.

Tilapia nilotica L. is considered an important commercial fish in Ethiopia. It is found in majority of inland waters and is most consumed species in the country. The investigation were carried out between May 1975 and April 1976 to determine breeding period of the fish and fecundity. The main breeding season was between December and June. The number of eggs produced by a female depended on its size. Tilapia nilotica L. is a mouth-brooder. The danger of overfishing is especially great with a mouth-brooding species of Tilapia. Every brooding fish caught represents a loss to the fishery of all the brood as well as the adults. It is thought that the underestimation of these aspects was responsible for the biological overfishing in Lake Victoria (4). Because of their mouth brooding habits, many cichlids are vulnerable to inter-ference in breeding season by the fishing activities of man. Fishing methods such as seine netting, that capture females whilst carrying eggs or fry in their mouth results in heavy losses of fry and hence adult fish (8). In many countries, the only form of fish conservation is by means of closed seasons. This means that there is a period in each year, planned to coincide with the main breeding season when fishing on the commercial scale is prohibited. The fish are thus able to breed undisturbed for periods ranging from two to three months, after which commercial fishing is one more allowed. During the closed seasons, subsistence fishing is usually permitted to persons resident in the particular fishery. In the opinion of many fisheries experts, this is the best form of fish conservation, as it is the most readily enforceable for various reasons, and the fishery it totally protected from commercial exploitation during the breeding season. Because of their great economic values as food, Tilapia have been studied extensively. Boulenger (2) gives information on breeding habits of Tilapia nilotica. Lowe (5) in his study of the habits of several Tilapias in lake Nyasa, reported that there were fairly well defined breeding seasons for T. sake Lowe, T. squamipinnis Günther and T. lidole Trewqvas. Fryer and Iles (3) give a summary of facts known about breeding habits of Tilapias. The present work was undertaken to study breeding period and fecundity of Tilapia nilotica Linnaeus in lake Zwai in order to establish closed seasons for commercial fishing.