cleaner wrasse

:  any of a genus (Labroides) of small tropical wrasses found typically on coral reefs of the Indian and Pacific oceans that clean larger fish (such as surgeonfish) of parasites and dead tissue It has been known that a small fish called the cleaner wrasse eats parasites off larger reef fish and that it sometimes sneaks a nibble of skin mucus. — T. A. Frail et al., Smithsonian, September 2011 Customers respond by suspending their normal predatory instincts and hanging almost in a trance, mouths and gills open, while the cleaner wrasses work—often swimming inside the mouths of larger fishes to find the parasites. — John Vandenbeld, Nature of Australia, 1988