Blue tang

July 29, 2012, 11:32 pm
Content Cover Image

Blue tang surgeonfish (Acanthurus coeruleus). Source: J.E. Randall

The blue tang (scientific name: Acanthurus coeruleus) is a member of the surgeonfish family (Family Acanthuridae) that lives on coral reefs in the Western Atlantic Ocean and the Caribbean Sea.

caption Blue tang. Source: ''Reef Fish Identification'', New World Publications © 1994

Scientific Classification

Kingdom: Animalia (Animals)
Phylum:--- Chordata
Class:------ Osteichthyes (Bony Fishes)
Order:-------- Perciformes
Family:-------- Acanthuridae (Surgeonfishes)
Genus:----------Acanthurus
Species:----------- Acanthurus coeruleus (Bloch and Schneider, 1801)

Physical Description

Blue tang range from 12 to 39 centimeters in length.  The blue bodies of adults are laterally compressed with a yellow spine at the base of the tail.  

Their flattened shape and sharp caudal spines make it difficult for predators to swallow blue tangs.  Juveniles are bright yellow.

Distribution

Blue tangs are usually found in the tropics (24 - 26°C; 42°N - 11°S; 100°w - 4°w), ranging from New York to the Amazon delta in Brazil

They are found east to Bermuda and Ascension Island but are most common in the Caribbean Sea, coastal Florida, and in the Bahamas.

 

caption Distribution of the blue tang. Florida Museum of Natural History.

    

Habitat

Blue Tangs live primarily on hard-coral reefs at depths ranging from 2 to 40 meters.  They can also be found near soft corals, rubble, seagrass beds, and algal beds.  Young fish prefer areas with plenty of cover.  Breeding individuals congregate at flat, sandy areas between patches of reef.  

Feeding Behavior

Blue tangs are herbivorous as adults, feeding largely on filamentous algae.  They avoid eating calcareous material, like corals, because they lack the gizzard-like stomach of other surgeonfishes.  Individuals feed singly, in small groups, or in large aggregations numbering over 100 individuals.  Blue tangs also eat plankton.

Behavior

caption juvenile blue tang. Source: © Doug Perrine/Florida Museum of Natural History

Adult blue tangs have three social modes: territorial, wandering, and schooling. Territorial adults defend their home rage from other members of the species. Schooling adults are not aggressive.  Wanderer adults are not aggressive nor do they interact with other individuals like schooling fish do. Wanderers are mostly chased by other fish including Ocean surgeonfish and damselfishes.   Occasionally , Blue Tang form large multi-species aggregations with other surgeonfishes.

Blue tangs may benefit from forming schools for two reasons.  First, individuals may experience lower rates of predation when feeding in large groups.  Second, by feeding in groups, fish might be able to work together to overcome the territorial defenses of other fishes.  For example, a single blue tang is easily chased away by an aggressive damselfish defending its territory.  However, when a large school of blue tangs and their schoolmates try to feed on algae in a damselfish's territory, there is little that the damselfish can do.  When this occurs, the damselfish frantically, but ultimately fruitlessly, attempts to chase away their more numerous attackers while the school consumes all of the algae in their territories.

Blue tangs are active during the day, hiding in crevices on the reef at night to avoid predators.

Juvenile blue tangs are solitary and occupy home ranges that increase with body size. Juveniles aggressively defend their home ranges from juvenile ocean surgeonfish. Juveniles also avoid damselfishes that overlap in range with them.

Reproduction

caption Acronus larvae of the blue tang. Florida Museum of Natural History.

Spawning occurs in the late afternoon three to eight days following the full moon in the winter months. It is likely that offshore currents, moon phase, predator abundance, and light levels all play a role in determining when spawning aggregations occur.   Generally, spawning aggregation sites are also used by ocean surgeonfish and parrotfishes. Blue tangs generally mate in large resident aggregations over sandy patches between reefs. These fish seem to prefer locations six to 10 meters deep with reasonably strong currents to sweep the fertilized eggs to sea.  Adults indicate their readiness to mate by changing color from a uniform deep blue to pale blue on the front half of the body and dark blue on the rear half of the body. Courting females and a small number of males break off from the aggregation and release gametes at the water's surface in a behavior called a "spawning rush."  Often, spawning rushes are not successful and are broken off by the female.  Pair spawning is limited to small populations.

Fertilization occurs in the water column; after the eggs hatch the larvae, known as acronurus, enter the pelagic stage.   The acronurus larvae eventually drift inshore, where they metamorphose into juveniles which takes about a week.  After metamorhphosis, when the fish are approximately 5 centimeters in length, the juveniles settle onto the reef.  Individuals reach sexual maturity after one year and may live for 12 to 15 years.

Associations

Blue tangs are preyed upon by a variety of predatory fishes including bar Jacks and Nassau groupers.

Blue tangs help keep algae populations under control, which prevents the overgrowth and suffocation of corals. Increases in algal density have greatly increased blue tang population size.

At Fernando de Noronha Archipelago in southwestern Atlantic, juveniles hold cleaning stations together with doctorfish and sergeant majors and graze algae as well as pick molted skin and parasites from green sea turtles (Chelonia mydas). This behavior is preceded by a characteristic inspection usually followed by feeding nips on the turtles’ skin (head, limbs, and tail), as well as on the carapace. The most inspected and cleaned body parts are the flippers.

Conservation Status

The blue tang is widespread and abundant so it is not at risk.

Refences and Further Reading

 
Glossary

Citation

McGinley, M. (2012). Blue tang. Retrieved from http://www.eoearth.org/view/article/150704

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