CBC News reports that scientists have found that male cleaner fish will punish their female partners if they do something that offends the larger client fish they are cleaning.
This "third-party punishment" is surprising because the males don't appear to be directly harmed by the females' behaviour.
Nichola Raihani of the Zoological Society of London and colleagues at the University of Queensland, Australia, and the University of Neuchtel, Switzerland, say their study could explain the evolution of apparently altruistic behaviour in other species, including humans.
The bluestreak cleaner wrasse (Labroides dimidiatus) is a cleaner fish that lives in coral reefs and eats parasites that grow on larger "client" fish.
The fish will occasionally try to sneak a larger meal by eating some of the mucus from the skin of the larger fish, but this upsets the client fish...MORE
Photo by Gerry Adams