Why do cleaner wrasses pick parasites off bigger fish?

Cleaner wrasses have a feeding relationship with larger fish in which they remove parasites, damaged tissue, and sometimes excess mucus. The cleaners gain a meal, while the clients benefit from reduced parasite loads and less irritation. This behavior is common on coral reefs and can even involve “cleaning stations” where many fish line up to be serviced. Research has shown that some fish remember good cleaners and may punish dishonest ones that bite healthy tissue instead of parasites. The relationship is a classic example of mutualism in the sea.