Nile Tilapia, Oreochromis niloticus (Teleostei: Cichlidae): a threat to native fishes of Lake Malawi?

The Nile Tilapia, Oreochromis niloticus, is a freshwater cichlid indigenous to the tropical and subtropical parts of the eastern and western Africa and is being cultured in the Lake Malawi catchment on the Tanzanian side. Historically, the Nile Tilapia has been successful in dispersing once it has been introduced into a catchment area. The probability of the Nile Tilapia successfully colonizing Lake Malawi is enhanced by many of its life history attributes including its fast growth rate, large size relative to native Oreochromis spp., and its diverse repertoire of feeding options. Where introduced, Nile Tilapia has had devastating impacts through competition or hybridization with native congenerics. We contend that the Nile Tilapia is a significant threat to the native fishes of Lake Malawi. With Lake Malawi harboring more species of fishes than any other freshwater lake in the world, a loss of species diversity due to the introduction of Nile Tilapia would be catastrophic for this unique system. Native fishes that in recent years provided 70% of the animal protein consumed in the country would be threatened by the colonization of the Nile Tilapia. We are convinced that should the Nile Tilapia become established in Lake Malawi it would (1) Cause the extirpation/extinction of native fishes, (2) Hybridize with endemic Oreochromis spp., and (3) Damage the livelihoods of existing artisanal fishermen.