Cichlids Under Threat

The huge diversity of cichlids in Lake Victoria has declined sharply since the mid-twentieth century. An estimated 200 or more of the lake's endemic cichlid species have disappeared or become extremely rare. Because the species are endemic, their loss from the lake means global extinction.The main threats are:1. Introduced predator. The Nile perch, a large predatory fish, was introduced into the lake in the 1950s to support commercial fishing. Its population increased rapidly in the 1980s, and it ate huge numbers of cichlids.2. Eutrophication. Fertiliser run-off from farms, sewage and soil erosion from deforestation have added nutrients to the lake. This causes algal blooms, which reduce light and, when the algae decompose, reduce oxygen in deeper water.3. Loss of mate choice. The algal blooms make the water cloudy (turbid). Because cichlid species are kept apart by females choosing males by colour, in murky water females can no longer tell the colours apart. They mate with males of other species, and the hybrids are fertile. The separate gene pools merge back together, so species are lost through hybridisation. This reverses the sympatric speciation that produced them.4. Invasive plants such as water hyacinth, overfishing and pollution have also caused damage.Conservation measures include reducing nutrient run-off, controlling Nile perch numbers, and keeping populations of threatened species in captive breeding programmes in aquariums and zoos, so they could later be returned to the lake. In some parts of the lake where water has become clearer, some cichlid species have started to recover.