Mutualism and the Cleaner Wrasse (Labroides Dimidiatus)

Since youth we have learned that the ocean covers approximately 70% of the earth’s surface.  Being home to more than 120,000 known ocean species, the ocean is witness to all types of relationships and interactions (Collins, 2010).  Among the most popular are parasitism and commensalism.  Parasitism is a symbiotic interaction where one organism (the parasite) gets its nutrition from another organism (the host) who usually is harmed in the process.  Commensalism is a relationship in which one organism benefits while the other simply remains neutral (Campbell, 2008).  Then lastly there is mutualism, which is defined as “an interspecific interaction that benefits both species”; a common relationship that can be found among a variety of paired animals (Campbell, 2008).  One interesting example is that of the Cleaner Wrasse (Labroides phthirophagus) and other marine organisms.

These tropical fish are widely distributed and are known to be found along the shallow reefs at an average depth of 1-30 meters in the Red Sea, and in the Indian and Pacific Ocean, from Hawaii to the East Coast of Africa (fishbase.org).  They can reach ~14 cm at the end of their four year lifespan and range from blue to yellow in color, often being recognized by a lateral bold stripe (fishbase.org).  As one might guess, the cleaner wrasses get their name from their mutualistic relationship with other fish (Brough, 2006). They “clean” fish at so-called cleaning stations by eating small parasites, mucus, dead skin, scales and other debris  from the gills, fins, and mouths of the fish; forming a symbiotic relationship (Waikiki Aquarium, 2009).  These obligatory feeders have specially structured mouths with teeth that act as tweezers, allowing them to remove debris from the host fish without fail (Brough, 2006).  Each cleaning station is run by either a group of juveniles, a pair of adults, or by a dominant male fish with his harem of females, and is set up in their territorial district along the reef (fisbase.org). In situations like the last mentioned, a female will switch her gender, and take over as a functional male once the dominant male dies and continue his duties, a biological process known as hermaphroditism (fishbase.org).  Amazingly, on occasion there have been reports of over one hundred fish being gathered at these cleaning sites at one time, with some single wrasses servicing over 2,000 fish a day (Brough, 2006).

In order to attract customers, the cleaner wrasse advertises by performing a rocking dance, in which it swims up and down, moving its tail in a zigzag like motion (fishbase.org; Horton, 2010). This “dance” usually puts the other fish in a coma-like state, demonstrating their “receptiveness for the cleaning”, by floating still in the water column making it easier for them to be cleaned by the wrasse (Brough 2006; Waikiki Aquarium, 2009). Upon seeing the signal, other fish simply line up with their mouths wide open and fins spread away from the body, ready for purification (Waikiki Aquarium, 2009). The official cleaning consists of the wrasse running along the entire fish’s body, eating debris from between the gills, teeth, and fins (Casado, 1996). While cleaning the insides of the larger fish’s mouth, the wrasse continually vibrates as a reminder of its presence, allowing them to avoid injury or death by the larger fish (Casado, 1996).  Once the host fish has had enough, he will twitch to alarm the wrasse to stop the cleaning (Brough, 2006).

The foundations of this mutualistic relationship are simple- they are health-related. The wrasse benefits by receiving its necessary nutrition from a protein-rich parasitic, debris-filled meal and the host fish benefits by being free of annoying parasites and getting a vibrating massage (Brough, 2006; Casado, 1996). The wrasse also benefits by being protected. It has been found that the host fishes will commonly defend the cleaning station and its fish from other potential predators (Casado, 1996).  It is rare to have a variety of fish species in such close proximity get along; however, because cleaner wrasses have a symbiotic relationship with many other reef animals, cleaning stations are exceptions in which these different fish share a common desire- to get clean (Brough, 2006; Casado, 1996).

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- Tiara Stark

 

References

-Brough, C.  2006. “About Cleaner Wrasses, Labroides, Family: Labridae.”  Animal-World, Dr. Jungle Exoic Pets, Animals, Aquariums.  Extensive Encyclopedia of Animal

 Information.  Animal World.

-Campbell, N.  Reece, J.  2008: Biology: 8th edition.  Published by Benjamin Cummings, San Francisco, California, 1267 pp.

-Casado, M. 1996. “The Cleaner Wrasse- Helping to Keep Fish Parasite Free, Belize Barrier

Reef.”  Belize Vacations, Tours, Resorts, News, Hotels, Travels, Flights, Weather,

 Maps, Real Estate.  Casado Internet Group.

-Cheney, K. 2011.  Cleaner wrasse mimics inflict higher costs on their models

when they are more aggressive towards signal receivers.  Biology Letters.

-Collins, T.  2010. Marinespecies.org: How many fish (and other species) in the sea?

-Fishbase.org: Labroides dimidiatus (Bluestreak cleaner wrasse).

-Horton, S.  2010.  Factors affecting advertising in Indonesian adult and juvenile

bluestreak cleaner wrasse (Labroides dimidiatus).

-Sale, P.  1991: The Ecology of Fishes on Coral Reefs.  Published by Academic Press, San Diego, California.

-Waikiki Aquarium.  2009. “Marine Life Profile: Hawaiian Cleaner Wrasse”.  Education Department, UH Manoa.

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