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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