A study done on Perissodus microlepis, a cichlid from Lake Tanganyika in Africa shows that opposites attract. The cichlid is a scale eater that eats scales from other fishes. Specimens have a mouth that either open to the left or the right. This adaptation makes it easier to tear scales from other fishes when feeding. The study showed that this species prefers to pair up with a partner that has a mouth that opens the opposite way of their own. During the course of the researches who completed the study (2004-7) caught 24 Perissodus microlepis pairs. 21 of those pairs had their mouths facing opposite sides. This is the first time disassortative mating have been confirmed in the wild. (Disassortative mating is to choose partners who differ from oneself to avoid inbreeding.)

The study was done by Japanese researchers including Kyoto University researcher Tetsumi Takahashi and was announced Wednesday in the online edition of “Biology Letters” published by the Royal Society.