Wiktionary
n. (context biology English) Any of many unrelated fish that provide a service to other fish species by removing dead skin and parasites
Wikipedia
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.
Usage examples of "cleaner fish".
Sometimes when he felt this way, he would swim to the edge of a coral reef and lie there in the sand while neon cleaner fish nipped at the parasites and algae on his scales.