Impact of fish species introductions on the tilapias of Lakes Victoria and Kyoga

Abstract

Early in the twentieth century, Oreochromis esculentus and O. variabilis were the most important fish species in a diverse multispecies fishery in Lakes Victoria and Kyoga, exploited by traditional fishing gears such as spears, fish weirs and fish baskets (Graham, 1929). Stocks of the two tilapias were abundant; excellent catches were obtained with little effort. However, yield to the fisherman of O. esculentus and O. variabilis, as well as that of other popular fishes such as Bagrus docmac and Labeo victorianus, declined steadily over several decades under increasing exploitation pressure using mainly flax gill nets, which were later replaced by synthetic fibre nets (Beverton, 1959; Garrod, 1960; Chapter 2). This steady decline largely contributed to the decision to introduce several tilapia species into Lake Victoria and the lakes of the Kyoga Basin (Kyoga lakes), ostensibly to boost fishery production. The introduction of non-indigenous fishes into the two lake systems as a management measure later included predatory Nile perch, Lates niloticus.