Related FAQs: Cleaning Symbiosis Among Fishes, Biological Cleaners, Related Articles: Using Biological Cleaners, Medicines/Treatments for Marine Diseases, Cleaner Shrimps, Genus Labroides Wrasses, Genus Bodianus (Hogfishes),  Cleaning Symbiosis Among Marine Fishes
By Bob Fenner	Lysmata Shrimp cleaning an "ichy" Naso

    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. 

Mutualistic Relationships. An example here of the endosymbiotic zooxanthellae of Giant Clams... the Algae get a home of relative protection from predators, changing water conditions... and the tridacnids receive some sugar nutrition and oxygen, removal of carbon dioxide...
Commensal Relationships: like the Pygmy Seahorse here so well disguised on a Muricella species Sea Fan... the Horse gets camouflage on the Fan, avoiding predation, and neither benefits nor does little to no harm to its host.
Parasitic Relationships: Where one species of the two benefits at their hosts loss. Here is a copepod crustacean parasite infested Bryaninops loki goby in the wild.

    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. 

The Indo-Pacific wrasse genus Labroides comprises species that are obligate cleaners, making almost all their nutrition from the removal of ectoparasitic crustaceans from other fishes. Below, the most common Cleaner Wrasse, Labroides dimidiatus, in an aquarium and a pair on their cleaning station in the Red Sea, working over a Parrotfish "customer".

   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. 

Most cleaners clean throughout their lifespans but there are exceptions. Larabicus quadrilineatus (Ruppell 1835), the Fourline or Arabian Cleaner Wrasse is actually a cleaner only as a juvenile Below at left, adult at right. As adults (they only get to five inches) the Fourline Wrasse mainly feeds only on coral polyps. Other notable examples are Atlantic Bodianus Wrasses, some Chaetodonts.

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".

Some Gobiosoma goby species to consider. The most common G. oceanops cleaning another ocean's Pseudanthias in an aquarium, G. evelynae, another readily commercially produced species, and a more exotic G. prochilos off of Mexico's Cancun. One to a tank is about all one needs, wants... they may fight otherwise. Look for the tank bred and reared ones... much hardier, adaptable to aquarium care.

Non-vertebrate choices abound. Some notable species in the Genus Lysmata below: Lysmata debelius Bruce 1983, the Scarlet Cleaner Shrimp, Blood Shrimp. Lysmata grabhami (Gordon 1935), the Atlantic White-Striped Cleaner Shrimp. Lysmata amboinensis (De Man 1888), the Indo-Pacific White-Striped Cleaner Shrimp or Ambon Shrimp. Widespread in the tropical Indo-Pacific and Red Sea.

    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. 

Conclusion:

    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. 

Examples of facultative and obligate cleaners: Bodianus pulchellus (Poey 1860), The Spotfin or Cuban Hogfish. A cleaner when young. And the Hawaiian endemic, Labroides phthirophagus Randall 1958, Hawaiian Cleaner Wrasse, that must clean to survive.

Bibliography/Further Reading:

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.