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. However, the cleaner fish may sometimes cheat and consume mucus or tissue, thus creating a form of parasitism. A wide variety of fishes have been observed to display cleaning behaviors including wrasses, cichlids, catfish, and gobies. Similar behavior is found in a number of species of cleaner shrimp.
Cleaner fish advertise their services with conspicuous coloration, often displaying a brilliant blue stripe that spans the length of the body. This adaptation has evolved independently in many different species of cleaner fish, thus making it an example of convergent evolution. Other species of fish, called mimics, have been observed to imitate the behavior and phenotype of cleaner fish in order to gain access to client fish tissue. This is another example of convergent evolution, where multiple mimics have evolved independently to mimic the cleaner fish in their geographical area.
Diversity of cleaner fish
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.
While they do derive the majority of their nutrients by removing ectoparasites, cleaner fish will also feed on the mucus and tissue of the client fish, as these food sources have greater nutritional value. There is however a risk of terminating the cleaning interaction if the cleaner is too aggressive, and takes too much mucus and tissue. Because of this, cleaners seek a balance in feeding between ectoparasites and mucus/tissue .
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.
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.
Mimic species evolve body forms, patterns, and colors in order to imitate other species in order to gain a competitive advantage. One of the most studied examples of mimicry on coral reefs is the relationship between the mimic Plagiotremus rhinorhynchos (the bluestriped fangblenny) and the cleaner wrasse model L. dimidiatus. By imitating the appearance of L. dimidiatus, P. rhinorhynchos is able to approach and subsequently feed on the tissue and scales of client fish while posing as a cleaner.
The presence of the cleaner mimic, P. rhinorhynchos, has a negative impact on the foraging success of the cleaner model L. dimidiatus. P. rhinorhynchos feeds by eating the tissue and scales of client fish, thus making client fish much more cautious and panicky while at cleaning stations. It has been found that more aggressive mimics have a greater negative impact on the foraging rate and success of the cleaner fish. Additionally, when mimics appear in higher densities relative to cleaners there is also a significant decline in the success rate of the cleaner fish. The effects of the mimic/model ratio are susceptible to the dilution effect, whereby an increase in client fish allows both the mimics and the models to have more access to clients, thus limiting the negative effects that mimics have on model foraging success.
- 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.
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