Cleaner fish

Cleaner fish are fish that provide a service to other fish species by removing dead skin and ectoparasites. This is an example of mutualism, an ecological interaction that benefits both parties. 
A wide variety of fishes show cleaning behaviors. They include wrasse, cichlids, catfish, and gobies, as well as by a number of different species of cleaner shrimp. 
There is also at least one predatory mimic, the sabre-toothed blenny. It mimics cleaner fish but in fact bites off pieces of fin.