Lake Victoria is the second largest freshwater lake in the world and one of the youngest lakes in Africa. Despite its young age, it hosted a remarkable number of species which has attracted the interest of many scientists studying fish evolution: the lake had been characterized as an evolutionary miracle, hosting a variety of species including more than 400 cichlids.
Unfortunately, this is no longer the case as a great number of species have gone extinct due to an ecological cascade that caused the collapse of Lake Victoria’s ecosystem. The problems started with the introduction of two non-native species, the Nile Perch (Lates niloticus) and the Nile Tilapia (Oreochromis niloticus) in 1950. The Nile Perch, being a vicious predator of great dimensions, heavily preyed on all smaller fish and led most of them to extinction within 50 years.
The disappearance of all herbivore fish species leaded to an incredible increase in phytoplankton and consequently in bacteria, which feed on dead phytoplankton biomass. Such bacterial blooms, usually consume all the available oxygen and lead to a phenomenon known as eutrophication. The problem was enhanced by high levels of pollution originating from nearby cities and deforestation of the native vegetation in the lake shores, which lead to the overexpansion of a floating weed-species known as water hyacinth. The increased biomass of the latter is a further food source for bacteria, deteriorating the water quality even more.
The destruction of the lake ecosystem had devastating consequences for the cichlid populations, leaving only 200 Lake Victoria cichlid species. Some of the latter are maintained and breed in aquariums, in the framework of rescue programs aiming to prevent further extinctions. As scientists focused on potential solutions to the ecological problems of the lake, there are few studies on the cichlid species of the lake and as a result Victorian cichlids are hard to identify.
While not as diverse as Tanganyika cichlids or Malawi cichlids, the lake hosts remarkable specialists both considering food sources and habitats, e.g. some species are specialized in stealing eggs from the mouth of cichlid females who display the behavior of mouth-brooding. Some Lake Victoria cichlids can be extremely aggressive, as is the case with all African cichlids. Due to the variety in the size and aggressiveness of the species, single species tanks might be advantageous. Care should be given to provide the appropriate tank size and substrate according to the species preferences. The tank temperature should be maintained around 76-77 °F (24-25 °C), however, as the lake is not as alkaline as other African lakes, the pH should be kept around 7-9 and the hardness around 2-8.
Kocher D. 2004. Adaptive evolution and explosive speciation: the cichlid fish model Nature Reviews Genetics 5, 288-298
Axelrod H.R. 1993. The Most Complete Colored Lexicon of Cichlids
Darwin’s Nightmare by Hubert Sauper. film release: 2004