Cleaner fish

Cleaner fish are fish that provide a service to other fish species by removing dead skin and ectoparasites. This cleaning symbiosis is an example of mutualism, an ecological interaction that benefits both parties involved. However, the cleaner fish may sometimes cheat and consume mucus or tissue, thus creating a form of parasitism. A wide variety of fish including wrasse, cichlids, catfish, pipefish, and gobies display cleaning behaviors. Similar behavior is found in other groups of animals, such as cleaner shrimps.

Cleaner fish advertise their services with conspicuous coloration, often displaying a brilliant blue stripe that spans the length of the body. This adaptation has evolved independently in different species of cleaner fish, making it an example of convergent evolution. Other species of fish, called mimics, imitate the behavior and phenotype of cleaner fish to gain access to client fish tissue. This is another example of convergent evolution.

The best known cleaner fish are the cleaner wrasses of the genus Labroides found on coral reefs in the Indian Ocean and Pacific Ocean. These small fish maintain so-called cleaning stations where other fish, known as hosts, congregate and perform specific movements to attract the attention of the cleaner fish. Remarkably, these small cleaner fish safely clean large predatory fish that would otherwise eat small fish such as these.

While they derive the majority of their nutrients by removing ectoparasites, cleaner fish also feed on the mucus and tissue of the client fish, as these food sources have greater nutritional value. There is however a risk of terminating the cleaning interaction if the cleaner is too aggressive, taking too much mucus and tissue. Because of this, cleaners seek a balance in feeding between ectoparasites and mucus or tissue.

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Wikipedia