Ask the WWM Crew
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The term "symbiosis" means "living together". There are some further stipulations as to what we mean by biological symbiosis... that it be metabolically dependent, between dissimilar species... And you've likely heard of many types of symbiotic relationships: mutualistic, where both parties benefit; commensal, a situation in which one species benefits, the other is unharmed... and parasitic, where the symbiont gets something at the expense of its host.
There are many intergradations of these categories... it is not always easy to discern how, and to what extent relationships in the wild are interlinked.
Cleaning Symbiosis is a mutualistically beneficial behavior involving the removal of ectoparasites, diseased and necrotic tissue between cooperating species, providing removal of harmful and unwanted materials from hosts and food for cleaners.
The types of behavior and kinds of organisms involved as cleaners are highly varied, though examples of similar relationships and structure are widespread among both closely related species and those phylogenetically distant. This behavior may be so casual as to appear accidental, or alternatively involve integrated complex relationships, the hosts and cleaners being intimately, ecologically and physiologically dependent on each other.
Facultative or Obligate Cleaning, Or Somewhere In-Between?
The role of cleaning symbiosis as a source of nutrition is wide. It may be facultative, only providing a "side job/meal" or food supplement or it may be obligate, what the cleaner species must do for food collecting. Some cleaning organisms are highly specialized, physically and behaviorally, only being able to "make a living" by cleaning. Most cleaners are not so highly specialized however, deriving only part of their nutrition from this behavior. The majority of cleaners tend to a degree of non-obligate, to facultative relationships.
Aquatic cleaning symbiosis occurs worldwide, in tropical and temperate seas, even freshwater. Experiments have been inconclusive, but have at times hinted that cleaning is vital to fishes. Cleaners are key organisms in many community ecosystems, with large pelagics coming to "visit", and happy underwater photographers using such stations as waiting stations for taking shots.
Range of Phenomena
There are more than one hundred known species of shallow water/littoral fishes which engage in cleaning on a full to part time basis. Hosts include reef and pelagic animals; rays, sharks, bony fishes, marine iguanas, turtles, crustaceans, sea urchins, starfishes, even marine mammals. Best known families of cleaner fishes include Chaetodontidae (butterflyfishes), Labridae (Wrasses), Embiotocidae (Surfperches), Blenniidae... among others.
Many hosts assume unnatural positions in front of potential cleaners to signal their desires. They strike motionless, open-finned poses, on their sides, head up, head down, even upside down to get the cleaners attention. Several hold their gill covers open, allowing the filaments to be cleaned. Color changes are common among fishes seeking to be cleaned... some investigators have asserted that this may be a manifestation of stress-conflict... the customer caught between a desire to be cleaned and the pain thereof, and wanting to swim/run away... I think it's a mechanism for revealing by contrast the presence of "owees" and parasites.
Most of the commonly available cleaner species in the aquarium interest are rather non-specific re hosts and material removed, though there are some species that will only clean certain matter, species, groups in the wild.
Biological Importance... to Aquarists:
Though the role of cleaner fishes in the wild has been declared as vital in studies, the home aquarist is encouraged to utilize either small species of non-obligate cleaning fishes or their numerous invertebrate equivalents. The obligate species, like Labroides Wrasses fare poorly in capture, holding, shipping and captive conditions, the vast majority perishing along the way from reef to consumer... the few that "make it" to customers tanks often perish soon thereafter due to a lack of "customers".
Of course, our aquariums are better able to exclude parasitic and infectious disease agents than wild circumstances, and other countervailing strategies (quarantine, effective filtration...) are key to limiting exposure to disease-causing organisms in captivity... greatly diminishing the necessity of using cleaners.
It is likely that cleaning symbioses evolved out of a means of securing food for cleaners. Present day relationships display the full span of casual/facultative to absolute necessity/obligate circumstances.
Cleaner organisms have their place in the sea and our aquariums. The smaller, tank bred fish species that are facultative, and many non-fish cleaners.
Burgess, Warren E. 1981. The genus Labroides. TFH 2/81.
Castro, Alfred D. 1985. Is there a doctor in the house? FAMA 5/85.
Fenner, Robert. 1995. Notes on Cleaner Wrasses. TFH 5/95.
Herald, Earl S. 1980. Hail the Cleanerfish! TFH 7/80.
Jenkins, Robert L. 1981. Symbiosis revisited. No matter how well you may define or categorize, an organism will still be what it darn well pleases! FAMA 3/81.
Kerstitch, Alex. 1981. Cleaning symbiosis. FAMA 10/81.
Walker, Stephen D. 1981. When a Cleaner Wrasse Isn't... FAMA 11/81.