Trust in fish

Abstract

A mutually beneficial interaction between two species of fish turns out to involve the careful appraisal of one by the other — and the appropriately virtuous behaviour by the former while being watched. If we see someone do a good turn to someone else we are more inclined to help the altruist at some point in the future, rather than someone with a reputation for being selfish. This ‘image scoring’ behaviour is thought to help maintain human cooperation. Redouan Bshary and Alexandra Grutter now provide experimental evidence that it can also stabilize cooperation between non-human animals. The cooperation in this case is displayed by cleaner fish that remove ectoparasites from their partners in a mutual relationship, the ‘client’ fish. The cleaners may cooperate in the task of removing parasites; or a cleaner fish may ‘cheat’ and simply feed on client mucus leaving the other cleaners to do the work. A series of foraging experiments shows that client fish engage in image scoring, and that the cleaners cooperate more in the presence of an image-scoring client.