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Paracanthurus hepatus is a species of Indo-Pacific surgeonfish. A popular fish in marine aquaria, it is the monotypic of the genus Paracanthurus.
A number of common names are attributed to the species, including regal tang, palette surgeonfish, blue tang (leading to confusion with the Atlantic species Acanthurus coeruleus), royal blue tang, hippo tang, blue hippo tang, flagtail surgeonfish, Pacific regal blue tang, and blue surgeonfish, hepatus tang, Indo-Pacific blue tang, regal blue surgeonfish, wedge-tailed tang, wedgetail blue tang.
It is most closely related to genus Zebrasoma, with which it forms a sister group.
Paracanthurus has small small scales, each with short ctenii on the upper surface. Scales on the caudal spine possess ctenii approximately three times as long as scales on the rest of the body. Scales anteriorly placed on the head between the eye and the upper jaw are larger with tuberculated, bony plates. This fish has a compressed, elliptical body shape, and a terminal snout. It has nine dorsal spines, 26–28 dorsal soft rays, three anal spines, and 24–26 anal soft yellow rays, and 16 principal caudal rays with slightly projecting upper and lower lobes. Its pelvic fin is made up of one spine and three rays; this characteristic is considered a synapomorphy of the Naso and Paracanthurus genus. The caudal peduncle has a spine located in a shallow groove, which is also a characteristic of its sister taxa Zebrasoma. It has 22 vertebrae. Paracanthurus has teeth that are small, close-set, denticulated, and described as incisor-like.
Jaw morphology includes an ectopterygoid that links the palatine to the quadrate bone near the articular condyle. A crest is present on the anterodorsal surface of the hyomandibular. The opercle is less developed, with a distinctly convex profile.
Some slight variation in appearance is present within Paracanthurus. The lower body is yellow in west-central Indian Ocean individuals, and bluish in Pacific individuals (4). Additionally, the blue color on the trunk of Paracanthurus loses pigmentation in response to changes in light and/or melatonin levels, making its appearance slightly lighter in color at night.
/ref> Vagrants were found two separate occasions in Hawaii, and are assumed to be aquarium releases.
Paracanthurus is an extant taxon resident in the following territories: American Samoa; Australia; British Indian Ocean Territory; Brunei Darussalam; Christmas Island; Cocos (Keeling) Islands; Comoros; Cook Islands; Disputed Territory (Paracel Is., Spratly Is.); Fiji; French Southern Territories (Mozambique Channel Is.); Guam; India (Nicobar Is., Andaman Is.); Indonesia; Japan; Kenya; Kiribati (Kiribati Line Is., Phoenix Is., Gilbert Is.); Madagascar; Malaysia; Maldives; Marshall Islands; Mauritius; Mayotte; Micronesia, Federated States of ; Myanmar; Nauru; New Caledonia; Niue; Northern Mariana Islands; Palau; Papua New Guinea; Philippines; Réunion; Samoa; Seychelles; Singapore; Solomon Islands; Somalia; South Africa; Sri Lanka; Taiwan, Province of China; Tanzania, United Republic of; Thailand; Timor-Leste; Tokelau; Tonga; Tuvalu; United States (Hawaiian Is.); United States Minor Outlying Islands (US Line Is., Howland-Baker Is.); Vanuatu; Viet Nam; Wallis and Futuna.
The fish is important for coral health as it eats algae that may otherwise choke it by overgrowth.
Fishes in the family Acanthuridae, including Paracanthurus, produce altricial larvae that receive no v. parental care. After hatching, these larvae rely on yolk reserves in order to survive their first two to three days of life.
The regal blue tang is one of the most common and most popular marine aquarium fish all over the world, holding its place as the 8th most traded species worldwide. In 1997–2002, 74,557 individuals were traded in official tracked sales and in 2011 approximately 95,000 Paracanthurus were imported for use as a marine ornamental fish. When harvesting Paracanthurus in the wild, juveniles are specifically targeted since they are easiest to collect due to their tendency to travel in schools. Paracanthurus for human use are harvested in the wild rather than raised in aquaculture. Conservationists encourage efforts to switch to aquaculture in order to better preserve wild populations.
After the release of Finding Nemo in 2003, popular media outlets reported a rise in demand for clownfish, the co-star alongside blue tang in the movie, to such an extent the phenomena was coined the Nemo effect. However, the legitimacy of the Nemo effect was disputed by peer-reviewed analysis. Nonetheless, a similar wave of rumors circulated the internet following the release of Finding Dory in 2016. According to peer-reviewed analysis, online searches for blue tang increased for 2–3 weeks after the release of Finding Dory, though data on imports of Paracanthurus show there was no significant increase in imports of blue tang following the release of the movie.
However, it is threatened by overexploitation (mostly for the aquarium trade) and destructive fishing practices. Individuals for aquarium trade are predominantly wild caught, so monitoring of wild populations is needed to prevent overharvest. Since it is dependent on fragile coral reef habitats, habitat destruction also constitutes pressure in parts of its range. Of individuals in the family Acanthuridae, 80% have experienced a 30% loss of coral reefs across their distribution. More research is needed to fully understand the effects of this loss on Acanthuridae. In an endeavor to mitigate the destruction of natural regal blue tang populations, efforts have been made to breed the species in captivity. It was successfully captive-bred for the first time in 2016, after a 6-year long effort by biologist Kevin Barden of Rising Tide Conservation.
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