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Marine Animal Encyclopedia

Blue Tang Acanthurus coeruleus


Species ID: A.AC

Description: A disk-shaped fish with a sloping forehead and high set eyes. Adults are deep blue to indigo, and can pale or darken the body at will. Fish of the family Acanthuridae are characterized by a sharp spine on either side of the tail, which is bright white or yellow in the blue tang. Sexes appear similar, and juveniles resemble adults except in their colour, which is bright yellow

Maximum Size: 40 cm (16 in)

Longevity: Up to 28 years

Status: Not currently on the IUCN endangered species list

Blue Tang & People: Consumed locally, but not important in commercial fisheries. However, this species is popular in the aquarium trade and is collected locally for export


Geographical Range: Very common in shallow waters throughout the Caribbean; rare or absent within the Gulf of Mexico

Coral Reef Zone: Commonly found in the back reef, reef flat and fore reef zones. May occasionally be found in the shore zone

Favourite Habitat: Blue tangs prefer shallow areas with coral rock and rubble on which algae can flourish

Depth Range: 2–40 m (6–131 ft)

A Day in the Life:

Dawn: Fish emerge from shelters and form feeding schools

Day: Typically found foraging for algae on the reef either alone or in large schools

Dusk: Schools begin to break up as fish seek night-time shelters. Spawning in large groups may occur from late afternoon to dusk

Night: Fish shelter in crevices or near large structures

Who Eats Who

The blue tang is herbivorous and grazes on algae. This fish is eaten by a variety of large reef predators including grouper, snapper, jacks, and barracuda.

Scuba Diver & Snorkeler Best Practices

Don’t stand on marine life : Never walk on the reef, no matter how shallow or devoid of life the reef may actually appear; a great deal of life on coral reefs may actually be invisible to the naked eye, and contact with these organisms may kill them. If you feel particularly uncomfortable in the water you may wish to wear a buoyancy aid. Additionally, always ensure your equipment fits before you enter the water; it is difficult to adjust when you are swimming and poor-fitting gear often results in snorkelers searching for a place to stand to order to make the necessary adjustments.


Blue tangs are somewhat wary and will move away if closely approached, but may be easier to get close to when feeding in the protection of a school.

Feeding Behaviour

Blue tangs are ravenous herbivores and are important for controlling the growth of algae, which competes with corals for space. While actively foraging during the day, blue tangs move in large schools that can number over 100 individuals. With strength in numbers, the schools are able to overwhelm the defences of territorial fishes, such as damselfishes which guard algae patches across the reef, and so gain access to this plentiful food source. Juveniles of this species feed on algae alone or may act as cleaners, feeding on the parasites of other fish.

Observe, record & share:

O A.AC-101 – School: A large group of blue tangs, and sometimes other species, moving over the reef and picking at the substrate

O A.AC-102 – Invasive feeding: A school that intrudes upon the territory of another reef creature, such as a damselfish, in order to feed on the defended algae patch

O A.AC-103 – Juvenile cleaners: Juveniles serve as cleaner fish and pick parasites off larger organisms at special locations known as cleaning stations

Attack & Defense Behaviour

Adult blue tangs are generally non-territorial in densely populated areas and territorial in less populated areas. Juvenile blue tangs are always territorial, regardless of population density. Territorial blue tangs repel intruders using fin displays, chasing and biting. If a confrontation becomes serious, blue tangs may thrash their tail in an attempt to wound enemies with their sharp tail spine. At night, blue tangs hide in crevices and adopt a nocturnal colour pattern of vertical black and white stripes that help camouflage them from predators while they sleep. Even when predators are able to find them, their large disc shape and spines make them difficult to swallow for many.

Observe, record & share:

O A.AC-201 – Hiding: At night, blue tangs shelter in reef crevices or caves

O A.AC-202 – Night colours: Night camouflage consists of vertical black and white stripes

O A.AC-203 – Defensive display: Raising the dorsal and anal fins to appear larger

O A.AC-204 –Territorial dispute: Territorial blue tangs repel intruders using fin displays, chasing and biting

O A.AC-205 – Spine: During an escalated conflict or when trying to escape a predator, a blue tang may thrash its tail to deliver deep, painful wounds with its tail spine

Reproductive Behaviour

Blue tangs are somewhat wary and will move away if closely approached, but may be easier to get close to when feeding in the protection of a school. These fish reproduce sexually by broadcast spawning and do not undergo sex change during reproductive development. At dusk, blue tangs move into deeper water, where males become more aggressive as they establish and defend temporary spawning territories. When ripe females approach, males assume spawning colours consisting of a pale head and pale tail stripe and attempt to align themselves with the female’s body. After a prolonged courtship dance, females and one or several males dart towards the surface in a classic spawning rush ending in the release of eggs and sperm. Spawning occurs in the late afternoon year round, with peaks in the winter months.

Observe, record & share:

O A.AC-301 – Male spawning colours: When ripe females approach, the males’ head becomes light and a tail stripe develops

O A.AC-302 – Temporary territoriality: Males defend temporary spawning territories

O A.AC-303 – Courtship: Males court females by exaggerated swimming and quivering

O A.AC-304 – Spawning Rush: A female and one to several males swim rapidly towards the surface and release a cloud of gametes

Highlight Behaviors

Invasive feeding: Blue tangs sometimes school to overcome the defenses of territorial algaecultivating fishes, such as the damselfish shown here. While the damselfish attempts to drive off intruders from one end of its territory, other blue tangs take advantage of the unguarded opposite end to graze on the damselfish’s well-tended algal lawn.

Did You Know?

• The geographical range of blue tangs extends considerably outside of the Caribbean, as far south as Brazil and as far north as New York.

• During the open-water (planktonic) stage of surgeonfishes, and many other broadcast spawning fish, a small droplet of oil in the egg provides both nourishment for the young fish as well as buoyancy to keep it floating in the water until it is large enough to hatch and swim under its own power.

• In areas such as Jamaica where the blue tang is overfished, the unchecked growth of algae threatens the well-being of the reef by smothering corals – a process which is accelerated by physical damage to corals by  boats, fishing nets, and careless swimmers.

What to do?

Share your observations today!: Discover your species of interest, observe its behaviour, and share your pictures and videos with friends and coral reef enthusiasts around the world! Upload media to the web, tagged with species common name (ex.: trumpetfish) and species ID code (ex.: A.AM) or species behaviour code (ex.: A.AM-101)

Blue Tangzoom image
  • Order Acanthuridae
  • Length 40 cm (16 in)
  • Weight Not recorded
  • Depth 2–40 m (6–131 ft)
  • Habitat Back reef, fore reef zones and reef flat
  • Distribution Throughout shallow waters in the Caribbean
Blue Tang habitat mapzoom image