Cleaner fish are fish that provide a service to other fish species by removing dead skin and ectoparasites. This Cleaning symbiosis is an example of mutualism, an ecological interaction that benefits both parties involved, though cleaning may grade into parasitism.
Cleaner fish advertise their services with conspicuous coloration, often consisting of a bold blue stripe the length of the body. By convergent evolution, different species of cleaner fish often resemble each other. There is also at least one aggressive mimic, the sabre-toothed blenny, that looks like a cleaner fish but in fact feeds on healthy scales and mucus.
Diversity of cleaner fish 
Marine fishes 
The best known cleaner fish are the cleaner wrasses of the genus Labroides found on coral reefs in the Indian Ocean and Pacific Ocean. These small fish maintain so-called cleaning stations where other fish, known as hosts, will congregate and perform specific movements to attract the attention of the cleaner fish. Remarkably, these small cleaner fish will safely clean large predatory fish that would otherwise eat small fish such as these. Cleaner wrasses appear to get almost all their nutrition through this cleaning service, and when maintained in aquaria rarely survive for long because they cannot obtain enough to eat.
Cleaning behaviors have been observed in a number of other fish groups. Neon gobies of the genera Gobiosoma and Elacatinus provide a cleaning service similar to the cleaner wrasses, though this time on reefs in the Western Atlantic, providing a good example of convergent evolution. Unlike the cleaner wrasses, they also eat a variety of small animals as well being cleaner fish, and generally do well in aquaria. However, the Caribbean cleaning goby (Elacatinus evelynae) will gladly eat scales and mucus from the host when the ectoparasites it normally feeds on are scarce, making the relationship somewhat less than mutually beneficial. The symbiosis does not break down because the abundance of these parasites varies significantly seasonally and spatially, and the overall benefit to the larger fish outweighs any cheating on the part of the smaller.
Brackish water fishes 
An interesting example of a cleaning symbiosis has been observed between two brackish water cichlids of the genus Etroplus from South Asia. The small species Etroplus maculatus is the cleaner fish, and the much larger Etroplus suratensis is the host that receives the cleaning service.
Freshwater fishes 
Cleaning is notably less common in freshwater habitats than in marine habitats. One of the few examples of cleaning is juvenile Striped Raphael catfish cleaning the piscivorous Hoplias cf. malabaricus.
Many cleaner fish have a distinctive combination of a long narrow body, a longitudinal stripe, a blue colour, and small size. "Convergent signalling among cleaners, using size, stripes and colour, should facilitate their recognition by fish clients."
The sabre-toothed blenny Aspidontus taeniatus is a blenny that mimics the ritualised dance the cleaner wrasse makes when passing fish swim by. Instead of providing a useful cleaning service, however, it bites off pieces of healthy skin and scales from the host before darting away to safety.
See also 
- Doctor fish, fish that provide a cleaning service to humans.
- Reciprocal altruism
- Social grooming, cleaning services offered between members of the same species.
- Surgeonfish, named for the scalpel-like blades near their tails.
- Tinca tinca, known as the "doctor fish" in the UK.
- Curry, O. "Morality as natural history." University of London Ph.D. Thesis. 2005. Accessed 2009-06-08.
- Helfman G., Collette B., & Facey D.: The Diversity of Fishes, Blackwell Publishing, p 380, 1997, ISBN 0-86542-256-7
- Robert M. Fenner (2001). The Conscientious Marine Aquarist, TFH, pp 282-283, ISBN 1-890087-02-5
- Cheney, K.L. & M. Côté. (2005) "Mutualism or parasitism? The variable outcome of cleaning symbioses." Biol. Lett. 1(2): 162-6.
- Richard L. Wyman and Jack A. Ward (1972). A Cleaning Symbiosis between the Cichlid Fishes Etroplus maculatus and Etroplus suratensis. I. Description and Possible Evolution. Copeia, Vol. 1972, No. 4, pp. 834-838.
- Carvalho, Lucélia Nobre; Arruda, Rafael; Zuanon, Jansen Zuanon (2003). "Record of cleaning behavior by Platydoras costatus (Siluriformes: Doradidae) in the Amazon Basin, Brazil" (PDF). Neotropical Ichthyology 1 (2): 137–139. doi:10.1590/S1679-62252003000200009.
- Stummer, Laura E., Jennifer A Weller, Magnus L Johnson, Isabelle M Cote (2004). "Size and stripes: how fish clients recognize cleaners". Animal Behaviour 68: 145–150. doi:10.1016/j.anbehav.2003.10.018.
- "Comparative shopping, a fishy invention?". CORDIS Express. Retrieved 2009-06-08.
- Froese, Rainer and Pauly, Daniel, eds. (2007). "Aspidontus taeniatus" in FishBase. 5 2007 version.
Media related to Cleaner fish at Wikimedia Commons