Characteristics of Fish and Fish Communities in Lake Tanganiyka

  Lake Tanganiyka, one of the oldest lakes in the world, has several million 
years of history. About 220 species of fish live in this lake, most of which 
are endemic. As two thirds of the fish, about 150 species, are the family 
Cichlidae (Perciformes), the lake is well known for the evolution 
and adaptive radiation of this family.
  The reasons such success by the Cichlidae are follows. First, they 
give protection to  their offspring such as mouth-brooding, and second, their
 mouth structure is transformable so that they can easily specialize into 
different kinds of food habitats.
  Offshore, in abyssal areas and in littoral areas, there exist fish 
communities of their own characteristics. Especially in rocky littoral areas, 
complex and stable fish communities,mainly composed of Cichlidae, have 
developed, where each species has its own food habitat and they coexist with 
complex species interactions.
  Recently, some interesting aspects of the ecology of fish have been 
discovered; for example, mouth-sidedness of scale-eating Cichlid Fish. There 
are two types, right and left sided, and the ratio in a population is kept 1:1 
through frequency-dependent natural selection exerted by prey alertness. Also, 
brood parasitism of a cat fish species has recently been revealed. Many 
cichlids keep their fertilized spawn in the mouth until their fry hatch out, 
but this cat fish makes its spawn creep into a cichlid fish's mouth, and the 
young cat fish grow in the mouth, eating the fry of the host cichlid.

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