Doctor Wrasse: little fish with a big job
There are a total of 131 identified species of fish and crustaceans that are “cleaners”. The fish usually have “cleaning stations” in areas of the reef where other fish can come and have their parasites and dead tissue removed. As this relationship is mutually beneficial for the cleaner and the client, predation on cleaner fish is massively reduced. They remove parasites from all over the fish’s body, in the gills and even inside the mouth. These fish are usually easily identified by bright blue conspicuous stripe along the sides of its body as an advertisement that it’s a cleaner fish. Although some fish such as the Bluestriped Fangblenny (Plagiotremus rhinorhynchos) has similar colours and markings of other cleaner fish which allows it access to clients healthy tissue while pretending to be cleaning.
Bluestreak Cleaner Wrasse
Bluestreak cleaner wrasse (Labroides dimidiatus) is a species of fish that are obligate cleaners. When an unfamiliar visitor arrives at the cleaning station, the fish usually begin manoeuvring their tails and displaying dance like movements. Bluestreak cleaner wrasse can be responsible for cleaning up to 100 different species of fish, and an individual fish can clean up to 2297 fish per day. The cleaning stations tend to be occupied by females with one dominant male. If the male disappears, one of the females will change their sex and become the dominant male within 14-18 days. Some individuals “cheat” and also take advantage of the client and feed on scales when parasites weren’t present. Although they never cheat fish large enough to severely punish them for what they’ve done. Keeping fish of all sizes from groupers to barracudas parasite free means these fish are vital in maintaining a healthy food web. This species of wrasse not only clean fish from the reefs, apex predators such as thresher sharks visit the reef to get cleaned by them.The video below shows them interacting and cleaning the mouth of a diver in the Red Sea.
The Bluetriped fangblenny (Plagiotremus rhinorhynchos) is an aggressive mimic of the bluestreak cleaner wrasse. It has similar colouration and patterns of juvenile wrasse so it can loiter around cleaning stations and attack the clients who are expecting to get a clean. This kind of behaviour is frequency dependent. If it happens too often, fish will stop using cleaning stations, if they aren’t frequent enough then they loose the opportunity for food. Because of this, bluestriped fangblennys also exhibit cleaning behaviour to ensure there is still lots of fish returning to them.
Garra rufa are a well known species of cleaner fish. They were made popular in the early 21st century as they were used in “Fish pedicure treatments” in spas. They are found in river basins around northern and central middle east (Turkey, Syria, Iran, Iraq). Studies have shown that these fish can help alleviate the symptoms of psoriasis, causing up to a 71% decrease in PSAI score (Psoriasis Area and Severity Index). In the natural environment, Garra rufa feed on aufwuchs (a collection of microscopic plants and animals on rock surfaces) so they do not exhibit symbiotic cleaning of other fish, but are still important in maintaining the physical habitat around them.
The bluestreak cleaner wrasse (Labroides dimidiatus) and the cleaner Goby (Elacatinus evelynae) both have distinct blue stripes along the side of the body and both are obligate cleaners. These species are not closely related and come from different oceans (Indian and Western Atlantic respectively). Blue is a low wavelength colour and travels further making it effective to fish further away that there is a cleaning station there. Both cleaner wrasse and gobies prioritise cleaning behaviour in potential predators than non-predatory fish. This is the first account that cleaners see their predators as a potential threat, and by prioritising them as clients. In the case of cleaning gobies, Parrotfish (which are generally quite parasite dense) will not get cleaned before a potentially deadly client, even if the client doesn’t have as many parasites on them. Predatory clients for bluestreak cleaner wrasse also receive a better quality cleaning experience then non-predatory fish.
The importance for a fish to remain parasite free and in as good condition as possible is evident. Fish wait around cleaning stations and wait while other fish are being cleaned rather than search for food or a mate. Cleaner fish have a vital role in keeping fish in multiple trophic levels healthy which allows for a healthy ecosystem. Cleaner fish arguably have one of the most important jobs on a coral reef. These fish have adapted their behaviour to the extremes of swimming inside the mouth and gills of their predators to prevent predation and to utilise that as a food source whilst still providing a valuable service.