A cleaning station is a location in a reef where sea organisms can take advantage of the services of parasitic and cleaner fish such as wrasses, cleaner shrimp, and gobies. Cleaning stations can be found in reefs all over the world's oceans, illustrating a rather remarkable mutually beneficial relationship which has evolved between parasitic fish and other ocean dwellers. In a sense, you could think of a cleaning station as a sort of fish carwash.
Parasitic and cleaner fish eat algae, parasites, and other materials which may become attached to the bodies of larger organisms. Typically, cleaner fish are able to clean the body of another animal without hurting it or damaging the mucus membranes which many animals use to protect themselves from infection. For cleaner fish, a cleaning station is advantageous, because it ensures that they have a steady supply of food.
For the “customers” at a cleaning station, these sites are immensely convenient. Parasitic infestations can kill fish, or impair their ability to swim, hunt, or mate. Even normally solitary species such as manta rays make take advantage of a cleaning station periodically to clear parasites, algae, and other material away from their gills, vents, and other body parts. Without a regular scouring, parasites and algae can clog the gills, making gas exchange difficult and essentially suffocating the fish, and they can also cause infections on the body along with other health problems.
At a cleaning station, fish which need to be cleaned swim up, and pose in a way which indicates that they are ready for cleaning. Cleaner fish typically work in teams, swarming the body of the client to feed, and sometimes swimming right into the mouth of the client to do an especially thorough job. By what appears to be a collective agreement, normally aggressive fish species do not attack the cleaner fish at a cleaning station, although unscrupulous individuals may regard a cleaning station as an open buffet when they are on the hunt.
Watching the action at a cleaning station can be quite interesting for divers and snorkelers. Often, a wide array of fish species can be seen, and a constant parade of new fish is rotated through the cleaning station. Biologists can also use cleaning stations as study sites to get a rough idea of the demographics of a fish population, and to look for signs of disease and disability in a fish population.