ABSTRACT
ABSTRACT During the past decades, dramatic changes were observed in the ecosystem of Lake Victoria. The introduced Nile perch (Lates niloticus) boomed in the 1980s and many other fish species disappeared. The more than 500 haplochromine cichlid species, that originally made up more than 80% of the demersal fish mass, were most severely affected. Within 10 years, they had almost vanished from the catches in the sublittoral and offshore waters, and lakewide, some 200 species may have disappeared. In the same period, the native zooplanktivorous cyprinid dagaa (Rastrineobola argentea) and the introduced Nile tilapia (Oreochromis niloticus) strongly increased in numbers. Concomitant with the changes in fish species composition, other changes in the ecosystem were also observed. Most prominent was the increase in eutrophication that had started already in the 1930s when a strong increase of the human population was also observed. As a result of soil runoff, eutrophication and phytoplankton blooms, dissolved oxygen concentrations and water transparency in the lake declined in the 1980s.
