Trust in Fish

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. This is yet another example of a complex social behavior once thought to be unique to mammals.


Credit: Nature Magazine

The small (wrasse) fish is a cleaner of its client (bream) fish. It removes parasites, but actually prefers eating the clients mucus, which is not in the client's best inrest (i.e. is non-cooperative). Bshary and Grutter found that eavesdropping clients (who observed cleaners working on other clients) spent more time next to 'cooperative' than 'unknown cooperative level' cleaners, which shows that clients engage in image-scoring behaviour. Furthermore, trained cleaners learned to feed more cooperatively when in an 'image-scoring' than in a 'non-image-scoring' situation.