primarily on female mosquitos. Fisheries Lake Victoria supports Africa's largest inland fishery (as of 1997). Initially the fishery involved native species, especially tilapia and haplochromine cichlids, but also catfish (Bagrus, Clarias, Synodontis and silver butter catfish), elephantfish, ningu (Labeo victorianus) and marbled lungfish (Protopterus aethiopicus). Some of these, including tilapia and ningu (Labeo victorianus), had already declined in the first half of the 20th century due to overfishing. To boost fishing, several species of non-native tilapia and Nile perch were introduced to the lake in the 1950s. Nevertheless, the natives continued to dominate fisheries until the 1970s where their decline meant that there was a strong shift towards the non-native Nile tilapia (now 7 percent of catches), non-native Nile perch (60 percent) and the native Lake Victoria sardine (30 percent). Because of its small size, the abundant open-water Lake Victoria sardine only supported minor fisheries until the decline of other natives. At the peak in the early 1990s, of Nile perch were landed annually in Lake Victoria, but this has declined significantly in later years. Environmental issues A number of environmental issues are associated with Lake Victoria and the complete disappearance of many endemic cichlid species has been called the "most dramatic example of human-caused extinctions within an ecosystem". Invasive fish Starting in the 1950s, many species have been introduced to Lake Victoria where they have become invasive and a prime reason for the extinction of many endemic haplochromine cichlids. Among the introductions are several tilapias: redbreast (Coptodon rendalli), redbelly (C. zillii), Nile (Oreochromis niloticus) and blue-spotted tilapias (O. leucostictus). Although these have contributed to the extinction of native fish by causing significant changes to the ecosystem, outcompeted natives and (in the case of the Nile tilapia) possibly hybridized with the highly threatened native tilapias, the most infamous introduction was the large and highly predatory Nile perch (Lates niloticus). As early as the 1920s, it was proposed to introduce a large pelagic predator such as the Nile perch to improve the fisheries in the lake. At the same time it was warned that this could present a serious danger to the native fish species and required extensive research into possible ecological effects before done. These warnings primarily concerned the native tilapia O. esculentus, as the smaller haplochromine cichlids (despite playing an important role in local fisheries) were regarded as "trash fish" by the colonial government. In the following decades, the