Dichromatism in relation to the trophic biology of predatory cichlid fishes in Lake Tanganyika, East Africa

A population of the piscivorous Tanganyikan cichlid, Lepidiolamprologus profundicola contains individually distinct pale and dark colour morphs: a dichromatism not related to age or sex. The 'dark form' frequently targets prey from the shaded space under rocks, while the 'plae form' targets prey in well-iluminated open water. This hunting site specialization is not ascribable to the differences of microhabitat that the predators of each form encounter. The main function of the dichromatism is apparently cryptic, as a camouflage for hunting. Interspecific comparisons among 19 species of carnivorous Tanganyikan cichlid fishes reveal that dichromatic taxa generally chase an active prey: fishes, scales of fishes or highly mobile free-swimming crustacea. In contrast, cichlid species foraging on a sessile or sluggish prey are monochromatic. This finding strongly supports the hypothesis that a pale-dark dichromatism serves to optimize foraging efficiency in predatory cichlids hunting an active prey.