Noun
English Wikipedia has an article on:cleaner fishWikipedia
cleaner fish (plural cleaner fishes or cleaner fish)
(zoology) Any of many unrelated fishes that provide a service to other fish species by removing dead skin and parasites.
Cleaner fish further Cleaning symbiosis : a small cleaner wrasse (Labroides dimidiatus) with advertising coloration services a big eye squirrelfish ( Priacanthus hamrur ) in an apparent example of reciprocal altruism. Source: Internet