Some possible factors leading to decline in fish species in Lake Victoria

Abstract

The decline in fish species in Lake Victoria is one of the largest documented losses of biodiversity in an ecosystem. The reduction in species in the lake was attributed to overexploitation through increased fishing capacity, use of illegal fishing gears and poor enforcement of regulations. Introduction of the predatory Nile perch is blamed for the decline of the native species, especially the haplochromine cichlids. The native tilapiines, Oreochromis esculentus and Oreochromis variabilis, declined due to hybridisation and competition with the introduced Oreochromis niloticus. Diversity loss in haplochromine cichlids has also been attributed to hybridisation caused by increased water turbidity, which reduces visibility in recognising conspecifics during breeding. Degradation of the environment through poor farming patterns and waste disposal has led to increased nutrients into the lake, in turn leading to changes in water quality, increased algal blooms and subsequent anoxia which led to frequent fish kills in the 1990s. However, recent resurgence of haplochromines thought to be extinct, disputes the fact that extinction of several species occurred. Though not denying that a drastic reduction in the number of native species occurred, the much hyped extinction could be a result of a lack of adequate information on taxonomy and ecology of the haplochromines as well.

Keywords:

• exotic introductions
• ecological changes
• hybridisation
• haplochromines