Scale-eating cichlids from Lake Tanganyika have mouths that twist either to the left or to the right and prefer to mate with partners bearing different traits.
Perissodus microlepis is a large cichlid and shows morphological dimorphism in the mouth opening direction, which enables it to feed on the scales on either the left or right side of its prey.
According to the results of a new study which is due to be published in the journal Biology Letters, Tanganyikan cichlid experts Takahashi and Hori of Kyoto University found that the scale-eating cichlid exhibited a mate selection process known as disassortative mating.
Perissodus microlepis with leftward pointing mouths (lefties) were more likely to breed with fish with rightward pointing mouths (righties) than they were to breed with fish with mouths pointing in the same direction as their own.
Previous studies have shown that pairings of lefty and righty Perissodus result in roughly equal numbers of lefty and righty babies, giving the offspring the greatest chance of survival.
The new results show that the cichlid chooses to mate with a partner bearing different morphological traits to its own, thus giving its offspring the greatest chance of surviving.
For more information see the paper: Takahashi T, Hori M (2008) - Evidence of disassortative mating in a Tanganyikan cichlid fish and its role in the maintenance of intrapopulation dimorphism. Biol Lett. 2008 Jun 24. .