Blue Tang Facts: Habitat, Diet, Behavior

The blue tang is among the most common aquarium fish species. Its popularity soared after the release of the 2003 movie "Finding Nemo" and the 2016 sequel "Finding Dory." These colorful animals are native to the Indo-Pacific, where they can be found living in pairs or small schools in the reefs of Australia, the Philippines, Indonesia, Sri Lanka, and East Africa.

While children may know the blue tang as "Dory," the fish has many other names. The animal's scientific name is Paracanthurus hepatus. It is also known as the regal blue tang, hippo tang, palette surgeonfish, royal blue tang, flagtail tang, blue surgeonfish, and Pacific blue tang. Simply calling it a "blue tang" can lead to confusion with Acanthurus coeruleus, the Atlantic blue tang (which, incidentally, also has many other names).

A Fish with Many Names

Appearance

Surprisingly, the blue tang isn't always blue. An adult regal blue tang is a flat-bodied, round-shaped fish with a royal blue body, black "palette" design, and a yellow tail. It reaches 30 cm (12 inches) in length and weighs around 600 g (1.3 lbs), with males typically growing larger than females.

However, the juvenile fish is bright yellow, with blue spots near its eyes. At night, the adult fish's coloring turns from blue to violet-tinged white, probably due to changes in its nervous system activity. During spawning, adults change color from dark blue to pale blue.

The Atlantic blue tang has yet another color-change trick: It's biofluorescent, glowing green under blue and ultraviolet light.

Diet and Reproduction

Juvenile blue tangs eat plankton. Adults are omnivorous, feeding on some plankton as well as algae. Blue tangs are important for reef health because they eat the algae that could otherwise cover the coral.

During spawning, mature blue tangs form a school. The fish suddenly swim upward, with females expelling eggs above the coral while males release sperm. Around 40,000 eggs may be released during a spawning session. Afterward, the adult fish swim away, leaving tiny 0.8-mm eggs, each containing a single drop of oil to keep it buoyant in the water. The eggs hatch in 24 hours. Fish reach maturity between nine to 12 months of age and may live up to 30 years in the wild.

Sword Fights and Playing Dead

Blue tang fins contain spines sharp enough to be comparable to a surgeon's scalpel. There are nine dorsal spines, 26 to 28 soft dorsal rays, three anal spines, and 24 to 26 soft anal rays. Humans or predators foolish enough to grab a regal blue tang can expect a painful and sometimes venomous stab.

Male blue tangs establish dominance by "fencing" with their caudal spines. Although they are armed with sharp spines, blue tangs "play dead" to deter predators. To do this, the fish lie down on their side and stay motionless until the threat has passed.

Ciguatera Poisoning Risk

Eating a blue tang or any reef fish carries the risk of ciguatera poisoning. Ciguatera is a type of food poisoning caused by ciguatoxin and maitotoxin. The toxins are produced by a small organism, Gambierdiscus toxicus, which is eaten by herbivorous and omnivorous fish (such as tangs), which in turn may be eaten by carnivorous fish.

Symptoms may appear anywhere from a half-hour to two days after eating an affected fish and include diarrhea, low blood pressure, and reduced heart rate. Death is possible, but uncommon, occurring in one in 1,000 cases. Regal blue tangs are strong-smelling fish, so it's unlikely a person would attempt to eat one but fishermen use them as baitfish.

Conservation Status

The regal blue tang is not endangered, classified as "least concern" by the IUCN. However, the species faces serious threats from habitat destruction of coral reefs, exploitation for the aquarium trade, and use as bait for fishing. To catch fish for aquaria, the fish are stunned with cyanide, which also damages the reef. In 2016, researchers at the University of Florida bred blue tangs in captivity for the first time, which raised the hope that captive-bred fish may soon be available.

Sources

• Debelius, Helmut (1993). Indian Ocean Tropical Fish Guide: Maledives [i.e. Maldives], Sri Lanka, Mauritius, Madagascar, East Africa, Seychelles, Arabian Sea, Red Sea. Aquaprint. ISBN 3-927991-01-5.
• Lee, Jane L. (July 18, 2014). "Do You Know Where Your Aquarium Fish Come From?" National Geographic.
• McIlwain, J., Choat, J.H., Abesamis, R., Clements, K.D., Myers, R., Nanola, C., Rocha, L.A., Russell, B. & Stockwell, B. (2012). "Paracanthurus hepatus". IUCN Red List of Threatened Species. IUCN.