The Rift Valley lakes are primarily known for the extensive radiations of fish species in the family Cichlidae
. Endemic species of the Clariidae
and other families are also found in these lakes.
A unique pelagic fish
community has evolved in Lake Tanganyika
including two endemic clupeids, Limnothrissa miodon
and Stolothrissa tanganicae
, that feed on zooplankton in the pelagic zone and, in turn, provide food for the four predatory centropomids, Lates angustifrons
, L. mariae
, L. microlepis
, and L. stappersii
Large numbers of cichlid species live adjacent to one another along the edges of the lakes. For example, one researcher caught 7,000 fish representing 38 families in one 4,300 square foot (400 sq. m) sampling area in Lake Tanganyika.
The cichlids have evolved specialisations to take advantage of their environment and to limit competition for resources. For example, one unusual group of fish, the scale-eaters, feed exclusively on the scales of other fish.
Most cichlids spend a lot of time caring for their young, but the young of mouth-brooders swim into their parent's mouth for protection in the face of imminent danger. It is not only the fish that are unique to these lakes.
, ostracods, shrimps, crabs, and mollusks are also represented by high numbers of endemic species. Lake Tana
supports a group of cyprinid fish that are all descended from a common ancestor (called a "species flock
"). This cyprinid
species flock is one of only two known in the world, and the only one that is still intact.