The best-known cleaner symbiosis is the cleaner wrasse which works at ‘cleaning stations’, picking parasites, dead skin and scales off reef fish. The cleaner wrasse gets a fed and the host rids its self of potentially harmful parasites. This is essentially a fish version of a spa.

However, there are many other cleaner species including damselfish, some triggerfish, sea chubs, gobies, cichlids, sticklebacks, suckerfish, sea perches and many others. Several invertebrate species also provide cleaning benefits such as shrimps. The ‘clients’ include rays, sharks, sea snakes, sea turtles, angelfish and even octopuses. The fact that the cleaner symbiosis is so widespread is proof that it is a particularly beneficial relationship, with many cleaner species such as the cleaner wrasse identified as being a keystone species; playing a large role in the ecosystem structure.

The study of the cleaner symbiosis has revealed complex behaviour is involved in the communication between the cleaner and client. Cleaners use signalling to communicate with their clients, for example a head nod indicates it is the clients turn, the cleaner will also sometimes headbutt the clients fins, signalling them to point them out for inspection, the cleaner will then vibrate its ventral fins against the parts that need cleaning, indicating to keep those parts available for inspection.

Cleaner fishes are also recorded to have a memory of their clients: who, when and where. This allows them to prioritize clients that have not had an appointment for the longest time. Cleaner fishes are also seen to be most attentive to those that they more likely to encounter again. For example, clients that occur in their home reef, thereby strengthening the relationship with their most reliable clients.

There are also false cleaner species which mimic the behaviour of the cleaners. For example, the saber-toothed blenny copies both the dance and appearance of the blue streak cleaner wrasse, once near enough they take a bite of the fins. These false cleaners are typically most successful with juvenile client fish which are inexperienced with cleaning. Adults have been observed to avoid and even attack false cleaners, providing evidence for a memory of previous attacks.