Lake Habitats: How Freshwater Fish Have Adapted

Freshwater fish live in an amazing variety of habitats. Evolution has shaped both their appearance and their senses over countless generations and millions of years to produce the most effective adaptations to fit the conditions in which they live.

What is it like living in a lake?

The still, clear waters of lakes provide an ideal habitat for fish. Free from any extreme fluctuations in temperature or water chemistry, these stable bodies of water are often home to teeming communities of fish. Nowhere provides a better example of this than the lakes of the Rift Valley in East Africa – the cichlids of Lake Malawi and Lake Tanganyika in particular are well known to aquarists. The waters of these lakes are brightly lit by the equatorial sun and are rich in food; both the algae and the invertebrates that the cichlids depend on are abundant. Both Malawi and Tanganyika are huge lakes and their isolation has produced in each a species flock that is endemic to its own lake — it has been estimated that Lake Malawi alone is home to around 450 species of cichlids. Almost all of these live in the clear, oxygen-rich waters of the shallows and most live among the complex, rocky substrate at the water's edge, which provides both a nursery for the young and the territories of the adults.

How are fish adapted for living in takes?

The African Rift Lakes are full of different habitats for fishes. Many species imported for the aquarium hobby are mbuna, which live along the rocky parts of the lake's shore. A long, thin body shape is ideal in this habitat as it allows the fish to maneuver around the rocks and into crannies and caves. Many fish that live in a current use their tail fins to propel themselves. However, Rift Lake cichlids often rely on their pectoral fins for this, which allows them to maneuver with pinpoint accuracy and, unusually for freshwater fish, it also allows them to swim backwards – ideal for investigating and then backing out of tight rocky crevices. Other Rift cichlid species, such as Nimbochromis livingstonii and Protomelas taeniolatus, are found in the sandy bays or open water of these inland seas.These species have deeper bodies than the mbuna, which are necessary for rotating the fishes in open water, or when feeding at the substrate. They also use a greater degree of tail-propulsion for their swimming.

Which senses do Rift Lake cichlids use most?

Light penetrates deep into the clear waters of the lakes so the cichlid's habitat is brightly lit under these conditions, vision s extremely important and this is reflected in the large eyes common to many of these fish. The brilliant colors of the cichlids, including vivid yellows and electric blues, and the dramatic patterns seen in many of the Tanganyikan cichlids, are also features of brightly lit environments because the fish use bold visual signals between one another. Nevertheless, the fish also use smell to back this up, especially when it comes to searching out hidden prey and assessing potential mates.

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