Colour variation of a shell-brooding cichlid fish from Lake Tanganyika

Abstract

The dwarf morph of Telmatochromis temporalis uses empty snail shells as shelters and spawning sites. This morph varies in body colour from pale to dark within populations. Pale individuals are likely to be cryptic on sandy-brown backgrounds through colour matching, but adaptive significance of dark individuals is unknown. The present study proposes two hypotheses for the occurrence of dark individuals: crypsis in darkness inside shells (darkness matching) and crypsis in irregular patterns consisting of shell shadows on sandy-brown backgrounds (pattern matching). The former hypothesis is less likely to be the main factor evolving dark bodies, because body darkness was not correlated with the amount of time that the fish remained within shells. Body darkness was correlated with shell density in their habitats, supporting the latter hypothesis because dark individuals may be able to mingle with shell shadows effectively at sites where shells were abundant. This study also found that body darkness was environmentally induced; therefore, this fish may shift between these anti-predator tactics (crypsis of pale individuals on sandy-brown backgrounds through colour matching and crypsis of dark individuals in irregular shadow patterns through pattern matching) by changing body darkness in response to shell density.