Blue Tang

The blue tang, also called the regal or palette surgeonfish, is an Indo-Pacific reef fish and the only member of its genus. It has a royal blue body, a yellow tail and a black palette-shaped marking on the back. It occurs from East Africa and Sri Lanka to the Philippines, Japan and the Great Barrier Reef, in clear outer reef areas and channels with moderate to strong current, at depths of 2 to 40 meters. Active by day, it lives in pairs or small groups of 8 to 14 and grazes on zooplankton and algae. Its feeding helps corals by removing algae that could otherwise overgrow them.

About the blue tang

The blue tang is a royal-blue surgeonfish with a yellow tail and a black "palette" pattern, found on coral reefs across the tropical Indian and Pacific Oceans. It is the only species in the genus Paracanthurus, in the surgeonfish family, Acanthuridae, and is most closely related to the Zebrasoma tangs.

Its scientific name is Paracanthurus hepatus. It goes by many names, including regal blue tang, palette surgeonfish, hippo tang, royal blue tang and wedge-tailed tang, and it is one of the most popular marine aquarium fish in the world. The name "blue tang" causes confusion, because it is also used for a different Atlantic fish, Acanthurus coeruleus.

The body is compressed and oval, with the snout at the very front of the head. Adults are royal blue. A broad black band runs along the back and loops down to the tip of the pectoral fin, enclosing a blue oval on each side that points toward the eye. The tail carries a bright yellow triangle edged in black. In fish from the west-central Indian Ocean the lower body is yellow, while Pacific fish are bluish below. The blue fades slightly at night in response to changes in light and melatonin.

Adults range from 12 to 38 cm (4.7–15 in) and usually measure 25 to 31 cm (10–12 in). They weigh about 600 g (21 oz), and males are generally larger than females. Juveniles look very different: they are bright yellow with blue spots near the eyes, turning blue as they mature. The scales are small, and the teeth are small, close-set and incisor-like. The small mouth lets surgeonfish pick algae from uneven surfaces.

A blue tang has a razor-sharp spine set in a shallow groove on each side of the caudal peduncle, where the tail joins the body. The spines are extended when the fish is stressed, and a quick sideways thrash of the tail can cause deep, painful wounds. The yellow tail triangle extends just past the spine, and the fish's bright colors are thought to warn predators of its venomous spine.

Behavior and diet

Blue tangs are diurnal. They live in pairs or small groups of 8 to 14 fish, and they school on the reef for protection, since few predators will swim into a group of fish slashing with sharp tail spines. Bar jacks and tiger groupers are among their predators.

When frightened, a blue tang, especially a juvenile, dives into branching coral and wedges itself in place by extending its tail spine into the coral, so a predator cannot pull it out. If spotted, it may even "play dead," lying motionless on its side until the threat passes.

Young blue tangs eat mainly plankton. Adults are omnivores that feed on zooplankton and graze filamentous algae, microalgae and other marine plants with their small teeth. By eating algae that would otherwise overgrow coral, blue tangs help keep reefs healthy.

Color also plays a part in social life. In fights, males circle one another and display their tail spines, and the hue of their blue changes as the encounter grows more intense.

Spawning can happen year-round, with peaks that vary by region. Groups gather over outer reef slopes in the late afternoon or evening, then rush toward the surface to release eggs and sperm into the water. Before spawning, the fish change from dark blue to pale blue. A female can release up to 40,000 tiny eggs, each about 0.8 mm (1/32 in) across with an oil droplet that keeps it afloat. Eggs hatch in about 24 to 28 hours, and parents give no care to the larvae.

Range and habitat

The blue tang lives throughout the Indo-Pacific. It is found on reefs off East Africa, Sri Lanka, Indonesia, the Philippines, Japan, the Great Barrier Reef, New Caledonia and Samoa, among many other places. A few vagrants found in Hawaii and the Mediterranean are thought to be released aquarium fish.

It favors clear water on exposed outer reefs and channels with moderate to strong currents, mostly 2 to 40 m (6.6–131 ft) deep in water around 24–26 °C (75–79 °F). Coral reefs are its main habitat, but it also uses seagrass beds, mangroves, algal beds and rocky reefs. Juveniles shelter in schools among Acropora coral, and the species is also found near cauliflower coral.

Blue tang vs Atlantic blue tang

Two different fish share the name "blue tang." They are in the same family but different genera and different oceans.

Adults are easy to separate. The Indo-Pacific blue tang has a bright yellow tail triangle and a bold black palette, while the adult Atlantic blue tang is plain blue with golden-blue fins. Young Atlantic blue tangs pass through a yellow phase and then a yellow-tailed blue stage before turning fully blue.

Conservation status

The blue tang is listed as Least Concern on the IUCN Red List (2012), and no population declines were found in that assessment. It is rare throughout its range but widely distributed, and its range overlaps many marine protected areas. Its population trend is unknown.

The main pressures are collection for the aquarium trade and destructive fishing. It is one of the most traded marine aquarium fish, ranked eighth worldwide, with around 95,000 imported in 2011. Most are wild-caught rather than farmed, and juveniles are targeted because they school and are easy to collect. Loss of coral reef habitat adds pressure. The species was bred in captivity for the first time in 2016, after a six-year effort, and conservationists encourage a shift toward aquaculture to protect wild populations.