Mara River and Associated Wetland as a Refuge of Threatened Indigenous Tilapiines of Lake Victoria, Tanzania

Abstract

A study was carried out in Mara River and Lake Kirumi in January/February, 2005 to investigate the importance of the wetland as a refuge site for indigenous cichlids particularly tilapiines which have either disappeared from Lake Victoria or threatened. Fish samples were obtained using experimental gillnets whose stretched mesh sizes ranged from 25.4 to 101.6 mm. The nets were set in the evening and retrieved early in the following morning. The catch was sorted into different species and their proportions according to number and weight was calculated. Gonadal maturity status was determined, and gut content was also analysed. Parallel to fish sampling, environmental parameters which included dissolved oxygen, conductivity, pH, concentration of silicon and phytoplankton composition were recorded. The results showed that Mara River recorded a higher (11 species types) fish species composition than Lake Kirumi (6 species types). The most dominant fish species in Lake Kirumi was Oreochromis niloticus which constituted 63.59% by weight followed by 0. esculentus (15.39%), which is an indigenous cichlid in Lake Victoria and has completely disappeared from the lake. The occurrence of 0. esculentus is a result of the dominance of its preferred food item in the environment, the diatom, Aulacoceira nyassensis which has disappellred from Lake Victoria. The diatom also dominated in the gut content of the fish species.

Keywords: Fisheries, Plankton, Nutrients, Macrophytes, Management

Tanzania J.Agric:Sc. (2007) Vol. 8 No.1, 25 - 30