The Evolution of Cichlids

Lake Tanganyika is famous for its amazingly rich profusion of different cichlid species. Many of them are endemic to the lake and can be found nowhere else in the world, not even in nearby lakes and waterways. Even though several other lakes in the African Great Rift Valley are home to a larger number of described cichlid species, Lake Tanganyika is where we find the most specialized and diverse cichlid collection. Over 95% of the described cichlids from Lake Tanganyika are endemic to the lake. The reason behind this high degree of specialization is a series of contributing factors and we can learn a lot about evolution by studying the situation in Lake Tanganyika. 

Lake Tanganyika is a very old lake – it was formed by tectonic forces approximately 20 million years ago – and the cichlids have therefore have plenty of time to evolve into different species. The environment in Lake Tanganyika is also very stable, and has been so for millions of years, which gives us a chance to see the result of millions of years up uninterrupted evolution. This sets Lake Tanganyika aside from many other famous freshwater lakes. Lake Victoria, the largest lake in Africa, is for instance no older than 400,000 years and has dried out completely no less than three times during its relatively brief history. Lake Victoria was actually completely dried out 14,800 years ago, so the aquatic life in it is not very old. The main reason behind this instability is the fact that Lake Victoria has a large surface area combined with a very limited dept; the deepest point is no further down than 84 meters and the mean dept is only 40 meters. Lake Tanganyika on the other hand is a narrow lake with a small surface area and a maximal depth of 1,470 meters. This makes Lake Tanganyika much more stable and less influenced by climate changes.

For millions of years, the cichlids of Lake Tanganyika has branched out; gradually becoming more and more specialized and evolved into a myriad of different species. It is no uncommon for a cichlid species in Lake Tanganyika to be adapted to a very limited environment and cichlids found just a few hundred meters away may very well have evolved into a completely different species. It is also common for cichlid species to display a rich profusion of colour variants depending on geographical location – unsurprisingly a fact that much treasured by aquarists.    

Lake Tanganyika is a rather closed system and this effect the fish fauna in at least two different ways. To begin with, it has caused a situation where a majority of the species hail from one single ancestor species who managed to get into the lake millions of years ago Secondly, it has lead to an extremely high degree of endemic species. When a new species evolve in Lake Tanganyika, it is very difficult for it to spread to other lakes and waterways. A large portion of the Lake Tanganyika cichlids are therefore endemic to the lake.

Over 200 species of cichlids have been described from Lake Tanganyika and fish experts suspect that the number will increase dramatically as the lake is more thoroughly explored by scientists. Today, several new species are found and described each year, despite the fact that large parts of Congolese and Tanzanian shore habitats are being far from methodically explored. If scientists were given a chance to survey the Congolese and Tanzania shores more systematically, the number of new discoveries each year would probably increase radically. New technology can also help us learn more about the situation in Lake Tanganyika, e.g. the advanced fishing equipment that is necessary in order to research the deeper regions of the lake.

A dire quandary is of course how environmental problems, such as pollution, over fishing and the introduction of invasive species, can cause endemic cichlids to vanish before we even have a chance to find and describe them. A lot of fish species within the African Great Rift Valley lakes are under threat today without even being known to us. Time, money and efforts must therefore be focused on conservational efforts; simply collecting, describing and researching the fauna is not enough.

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