Acanthurus coeruleus, Blue Tang [+]

Kingdom Animalia Phylum Chordata Class Actinopterygii Order Perciformes Family Acanthuridae Genus Acanthurus species: Acanthurus coeruleus [+ITIS +WoRMS]

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Description & Behavior

The blue tang, Acanthurus coeruleus (Bloch and Schneider, 1801), aka blue tang surgeonfish, blue barber, blue doctor, blue doctorfish, blur tang, yellow barber, and yellow doctorfish, is one of 75 species in the surgeonfish Family, Acanthuridae. This family of fishes are referred to as surgeonfish due to the very sharp, moveable spines on either side of the tail that resemble surgeons' scapels. Acanthurus is derived from the Greek "acantha" which means thorn, and the Greek "oura" which means tail.

The blue tang is a high-bodied, compressed, pancake-shaped fish with a pointed snout and small scales. The eye is located high on the head and the mouth is small and low on the head. The dorsal fin is continuous. Of particular interest is the distinct yellow caudal spine located at the base of the tail on either side of the body, a characteristic shared with other surgeonfish. This spine fits into a horizontal groove and can be extended and used to fend off aggressive encounters.

The blue tang reaches 39 cm in length, has 9 dorsal spines, 26-28 dorsal soft rays, 3 anal spines, and 24-26 anal soft rays. A deep-bodied surgeonfish with a conspicuous yellow caudal spine. Has the most distinctive coloration of all western Atlantic surgeonfishes.

This fish has three color phases. In its juvenile phase, it is bright yellow, changing to a mixture of yellow and blue during adolescence. There may be blue crescents above and below the pupils of the eyes. It may be spotted with blue or have a yellow body and blue fins.

As the fish matures into the intermediate phase, the color darkens to a bright blue or purplish-gray with a yellow caudal fin. Gray longitudinal lines are located in the flank region with blue dorsal and anal fins banded with orange-brown diagonal lines. The caudal spine is yellow to pale yellow or white. At night, blue tangs display white vertical stripes.

Adult blue tangs are deep blue to purplish-blue with a yellow caudal spine. The change from juvenile to intermediate to adult coloration is not size-dependent as some fish in the juvenile yellow phase may be larger than the adult blue phase.

World Range & Habitat

Reef-associated; marine; depth range 2-40 m tropical; 24-26°C; 41°N-33°S - Western Atlantic: New York, USA and Bermuda to the Gulf of Mexico and Brazil. Eastern Atlantic: Ascension Island. It is abundant in Florida, Bahamas, and the Caribbean Sea. In coral reefs, blue tangs live in holes and crevices where they are sheltered from predators while they sleep at night. The blue tang lives singly, in pairs, or in small groups of up to 10 or 12 individuals, although occasionally it forms large aggregations that forage about the shallow reefs, grazing on algae. These aggregations sometimes include doctorfish, Acanthurus chirurgus, and other surgeonfish. The juvenile blue tang is rarely seen on the reef due to its small size and need for constant cover from predators. The intermediate phase with the blue body and yellow tail is often observed on reefs while young adults are abundant everywhere on the reef.

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Feeding Behavior (Ecology)

The blue tang feeds entirely on algae. It grazes algae from rocky areas and browses filamentous algae, thereby avoiding large quantities of calcareous materials. Other surgeonfishes have heavier-walled, gizzard-like stomachs, and are capable of handling ingested sand and other calcareous materials. Blue tangs are important in keeping algae populations under control, preventing algae from overgrowing and suffocating corals.

Life History

Blue tangs reach sexual maturity at 9-12 months of age and lengths of 11-13 cm. Dioecism (refers to species in which sexes are always separate. Opposite of hermaphroditic and monoecious), external fertilization, onguarders, open water/substratum egg scatterers.

Spawning occurs during late afternoon and evening hours. This event is indicated by a change in color from a uniform dark blue to a pale blue anterior and dark blue posterior. Males aggressively court female members of the school, leading to a quick upward spawning rush toward the surface of the water during which eggs and sperm are released. The eggs are small, approximately 0.8 mm in diameter. The eggs are pelagic, each containing a single droplet of oil for flotation. The fertilized eggs hatch in twenty-four hours, revealing small, translucent larvae with silvery abdomens and rudimentary caudal spines.

The newly hatched larvae are referred to as acronurus because they were once thought to represent a separate genus of fish, Acronurus. The acronurus is diamond-shaped and laterally compressed, with a head shaped like a triangle. It has large eyes and prominent pectoral fins, and vertical ridges on the body. The dorsal fins, anal fins, and scales begin to develop when the acronurus reaches 2-6 mm in length. The caudal spine does not appear until the acronurus reaches about 13 mm in length. Late post-acronurus drift inshore, where they metamorphose into juveniles. The acronurus lose their silver color and turn brown, and their profiles become round. The prominent dorsal and anal spines that are characteristic of the acronurus reduce, and the snout elongates. Complete metamorphosis takes about a week, after which two-inch long juveniles settle onto the bottom of a suitable inshore habitat.