Blue tangs, Acanthurus coeruleus, live on shallow marine reefs throughout the western Atlantic Ocean, the Gulf of Mexico, and the Caribbean Sea. Blue tangs range from New York in the north to the Amazon delta in Brazil. They are found east to Bermuda and Ascension Island but are most common in the Caribbean, and coastal Florida and the Bahamas.

Biogeographic Regions: atlantic ocean (Native )

Acanthurus coeruleus reaches 39 cm in length. A sexually mature fish is typically over 10 cm in length. Adult coloration is deep blue and occasionally purple. Mature fish are able to temporarily change color between near-black and pale white. These color shifts can encompass the entire fish or portions of it and are different between the sexes. Similar to other fishes in the family Acanthuridae, Acanthurus coeruleus is a laterally compressed, pancake-shaped fish with high eyes, a subterminal mouth, yellow caudal spine at the base of the tail, and a dorsal fin that ends at the caudal peduncle. Juveniles are bright yellow. Older juveniles are blue or orange-brown with grey stripes. The sharp caudal spine is found in a horizontal groove on the peduncle and can be extended during aggressive interactions. Acanthurus coeruleus has 9 dorsal spines, 26-28 dorsal soft rays, 3 anal spines, and 24-26 anal soft rays.

Range length: 39 (high) cm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: sexes alike

Blue tangs live primarily on hard-coral reefs. 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. They shelter in coral holes and crevices. Blue tangs can be found at depths of 2 to 40 meters.

Range depth: 2 to 40 m.

Habitat Regions: tropical ; saltwater or marine

Aquatic Biomes: reef ; coastal

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. Acanthurus coeruleus individuals feed singly, in small groups, or in large aggregations numbering over 100. Large aggregations can and in these groups can ravish damselfish gardens on reefs. Blue tangs that live in smaller populations do more foraging in the water column. Blue tangs will also eat plankton.

Animal Foods: zooplankton

Plant Foods: algae; phytoplankton

Primary Diet: herbivore (Algivore)

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. Most blue tangs move within single reef habitats but they may also live on wider ranges around the reef.

Juveniles graze algae and pick molted skin and parasites from green turtles (Chelonia mydas) in cleaning stations with surgeonfish (Acanthurus chirurgus) and sergeant majors (Abudefduf vaigiensis).

Mutualist Species:

• surgeonfish (Acanthurus chirurgus)
• sergeant majors (Abudefduf vaigiensis)
• green turtles (Chelonia mydas)

Predators include reef sharks, tunas, snappers, jacks, groupers, and barracudas. Juveniles may also be taken by trumpetfish. Pelagic eggs are commonly eaten by small bar jacks, yellowtail snappers, and the black durgon.

Because of their flattened shape and sharp caudal spines, it is difficult for predators to swallow blue tangs.

Defense from predators while grazing and spawning is also accomplished by schooling. Attacks are more often observed on solitary fish.

Known Predators:

• tunas (Scombridae)
• groupers (Serranidae)
• jacks (Carangidae)
• reef sharks (Carcharhinidae)
• snappers (Lutjanidae)
• barracudas (Sphyraenidae)
• trumpetfish (Aulostomus strigosus)
• black durgon (Melichthys niger)
• bar jacks (Carangoides ruber)
• yellowtail snappers (Ocyurus chrysurus)

Blue tangs use vision to communicate and to locate food. They may also use chemical cues and touch, but little is known about communication and perception channels in these fish.

Communication Channels: visual ; tactile

Perception Channels: visual

Eggs take 24 hours to hatch. Upon hatching, the pelagic larvae are less than 2 mm in length. The young, called ""acronuri"", are transparent, silvery, and diamond-shaped. They begin to develop scales and dorsal and anal fins at 2 to 6 mm in length. The caudal spine appears when the larvae reach 13 mm in length. Older acronuri drift to nearshore areas where they meta morphose into juveniles, including losing their silver color, developing a more rounded profile, and developing an elongated snout.

Development - Life Cycle: metamorphosis ; indeterminate growth

Blue tangs live up to 12 to 15 years in the wild.

Range lifespan

Status: wild: 12 to 15 years.

Blue tangs generally mate in large resident aggregations over sandy patches between reefs. These fish seem to prefer locations 6 to 10 m deep with reasonably strong currents to sweep the fertilized eggs to sea. Mating readiness is indicated by color changes in the adults, who change 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.

Mating System: polygynandrous (promiscuous)

Prior to a spawning aggregation, small groups of fish travel from nearby reefs before forming schools of over one-hundred individuals. Although spawning aggregations typically occur every day at a given location, they are often restricted to less than 20 individuals. The largest spawning occurs in the late afternoon three to eight days following the full moon in the winter months. However, the exact variables contributing to spawning aggregations are still unknown. It is likely that offshore currents, moon phase, predator abundance, and light levels all play a role in predicting spawning aggregations. Generally, spawning aggregation sites are also used by Acanthurus bahianus and members of the genera Scarus and Sparisoma. Sexual maturity is reached after one year.

Breeding interval: Breeding occurs once or twice a year.

Breeding season: Breeding occurs year-round, but more often during winter.

Average time to hatching: 24 hours.

Average age at sexual or reproductive maturity (female): 1 years.

Average age at sexual or reproductive maturity (male): 1 years.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sequential hermaphrodite (Protandrous ); sexual ; fertilization (External ); oviparous

Parental care is absent in this species.

Parental Investment: no parental involvement; pre-fertilization (Provisioning, Protecting: Female)

Acanthurus coeruleus is a secure species. It is not on the IUCN Red list.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

Blue tangs can cause ciguaterra poisoning if eaten. Their sharp caudal spine can cause painful injuries if people try to handle them. Their sudden movements can cause the spine to create a deep wound, posing a risk of infection. Some species of Acanthurus may have venom associated with the spine as well.

Negative Impacts: injures humans (bites or stings)

Blue tangs are sometimes used as a bait fish. They are important in the aquarium trade, where they are popular fish. Blue tangs, and other reef fish, attract ecotourism in the form of snorkeling and diving.

Positive Impacts: pet trade ; ecotourism