Paracanthurus hepatusFlagtail surgeonfish(Also: common surgeon; doctorfish)

Geographic Range

Common surgeon, Paracanthurus hepatus, are strictly marine fish that typically inhabit tropical coral reefs in waters with a strong current. They may move seasonally, occurring at higher latitudes when water temperatures allow. Generally, common surgeon range between 30° north and south latitude and 32° east to 170° west longitude in the Indian and Pacific Oceans. Individuals found in other areas are presumed to have been released from aquaria. ("Palette surgeonfish", 2009; Froese and Pauly, 1991; Myers, 1991; "Blue Tang", 1999)


Common surgeon are strictly marine and can be found in tropical and sub-tropical coastal regions where temperatures are between 24 and 26 °C. They congregate near Pocillopora eydouxi, a type of coral with branching extensions, which serve as a protective hiding place when threatened. Reefs provide plant material, such as algae, necessary as food for common surgeon. Common surgeon remain at epipelagic depths between 2 and 40 m. ("Palette surgeonfish", 2009; Froese and Pauly, 1991; Myers, 1991)

  • Aquatic Biomes
  • reef
  • Range depth
    2 to 40 m
    6.56 to 131.23 ft

Physical Description

Common surgeon are characterized by the vibrant sky blue coloration of their oval-shaped bodies. Structures called iridophores on the exterior of the fish contribute to this coloration. Adults have dark narrow lines of dark blue on the dorsal half of their body. This color extends from the eye on the anterior end and continues to the posterior end. This coloration is darker near the posterior end and is black near the tail. A circular patch of sky blue coloration is located directly behind the pectoral fin. The pectoral and caudal fins are are bright yellow. The yellow extends in a "V" shape from the caudal fin to a point just beyond the caudal spine.

Coloration of common surgeon changes as they mature; juveniles are bright yellow with blue spots near their eyes, and their dorsal and anal fins are tipped in light blue. Their body becomes blue as they mature.

Adults range from 12 to 38 cm in length, averaging 25 to 31 cm. Common surgeon weigh on average 600 g. Males are typically larger than females. ("Palette surgeonfish", 2009; Goda and Fujii, 1998; "Blue Tang", 1999; "Blue Tang: Paracanthurus hepatus", 2010; Thresher, 1984; Winterbottom, 1971)

Because many surgeonfish are similiar in size and color, species of surgeonfish are distinguished by the number of spines they possess. Common surgeon have 9 hard, sharp spines in their dorsal fin followed by 19 to 20 soft rays. Their anal fins have 3 spines and 18 to 19 rays. Their pectoral fins consist of 16 rays, and their pelvic fins have 1 spine and 3 rays.

Common surgeon have a razor-sharp caudal spine located at the base of their caudal fin. This spine contains toxins that can cause a debilitating pain to small predators and uncomfortable irritation and pain in humans. The caudal spine rests in a groove below the surface of the skin and can be extended from the body. Its base is attached to the vertebrae of the fish by a ligament directly connecting the two. The outer point of the spine is free to move with contraction of specific muscles. When threatened, a common surgeon extends its caudal spine and attempts to puncture the exterior of a predator. (Goda and Fujii, 1998; Randall, 2001; "Blue Tang", 1999; Thresher, 1984; Winterbottom, 1971)

  • Sexual Dimorphism
  • male larger
  • Average mass
    600 g
    21.15 oz
  • Range length
    12 to 38 cm
    4.72 to 14.96 in
  • Average length
    25 to 31 cm


Larvae of common surgeon hatch about 26 hours after the small eggs are laid. Larvae are severely underdeveloped and lack a heart beat at hatching. Larvae are nourished by yolk from the egg. Newly hatched larvae are buoyant but remain in a resting state until the heart begins to beat, up to 5 hours after hatching.

Two days after hatching, fins and pigment in the eyes begin to develop, and larvae begin to make short swimming movements. Development continues with jaws and the gut, and by the seventh day scales and intestines begin to form. Speed of development is related to light intensity. Larvae mature after about 37 days.

Juvenile common surgeon resemble adults, however, they differ in coloration. Juveniles also have a more rounded caudal fin than adults. Additionally, the ventral and poster tips the caudal fin in adults extend beyond the middle section of the fin. (Randall, 2001; "Blue Tang", 1999; "Blue Tang: Paracanthurus hepatus", 2010; Thresher, 1984; Winterbottom, 1971)


Common surgeon congregate in breeding groups, composed of both males and females. These groups spontaneously form. Groups dissolve and reform several times prior to spawning. A group begins to swim upward and, at the crest of this upward movement, they release their gametes. Common surgeon are broadcast spawners; eggs and sperm are released directly into the water, and fertilization takes place externally. The quickened pace of their swimming during breeding is believed to allow for dispersal and mixing of the sperm and eggs. Eggs are then carried away by currents.

On occasion, common surgeon have been observed breeding with individual mates rather than in groups. In this case, a male's coloration may change. The male and female then circle around one another, showing off their coloration before breeding. (Randall, 2001; Robertson, 1983; Thresher, 1984)

Common surgeon breed during cooler months, though time of year varies with location and water temperature. In the Pacific, breeding activity is most intense from December to June. In locations where water temperature does not vary considerably with season, breeding can take place throughout the year. Breeding is assumed to peak during the summer in these locations, but common surgeon in these areas have spawning episodes throughout the year.

During months of prime temperature, females release their eggs about once a month. With each spawning event, females can release up to 40,000 eggs into the water column. High quantities of eggs and sperm make water cloudy in appearance. ("Palette surgeonfish", 2009; Randall, 2001; Robertson, 1983; "Blue Tang", 1999; Thresher, 1984)

Eggs of common surgeon hatch in 25 to 28 hours (average 26 hours). Larvae develop quickly and feed in great numbers off shore. Sexual maturity is not measured by age but rather by size. Males generally reach sexual maturity around 11 cm in length. Females, however, do not reach sexual maturity until about 13 cm in length. ("Palette surgeonfish", 2009; "Blue Tang", 1999; Thresher, 1984)

  • Breeding interval
    Common surgeon are believed to breed once monthly
  • Breeding season
    Common surgeon generally breed during cooler months, from winter to early spring.
  • Average number of offspring
    40,000 eggs per spawning session
  • Range time to hatching
    25 to 28 hours
  • Average time to hatching
    26 hours
  • Range time to independence
    4 to 7 days
  • Average time to independence
    5 days

There is no parental investment among common surgeon. As broadcast spawners, males and females disperse after releasing their gametes into the water column. (Randall, 2001; "Blue Tang", 1999; Thresher, 1984)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning


Common surgeon can live more than 30 years in the wild. In aquariums, where they more readily acquire diseases, common surgeon generally do not live more than 20 years and more commonly survive only 8 to 12 years. (Dunder, 2003; Finacom, et al., 2008)

  • Range lifespan
    Status: wild
    30+ (high) years
  • Range lifespan
    Status: captivity
    20 (high) years
  • Typical lifespan
    Status: captivity
    8 to 20 years
  • Average lifespan
    Status: captivity
    12 to 14 years


Although common surgeon are occasionally observed individually, most are found in pairs or small groups. In the reef, they school for protection. A group of fish, each possessing a sharp and venomous caudal spine is potentially problematic to predators; very few predators swim into the middle of a school of surgeonfish to feed off the members of the group. Common surgeon aggregate with other genera of surgeonfish, including Acanthurus, Ctenochaetus, Naso, Zebrasoma, and Prionurus.

Male common surgeonfish may have violent encounters with one another, circling each other and displaying their caudal spine. The hue of their blue coloration changes as the encounter becomes more intense. Males attempt to injure one another with their venomous spines, each one swimming closer to the other until its caudal fin can be manipulated to slash the other.

This caudal spine may have an impact on the social standing of common surgeon with the other marine fish in the area. A fish of this species achieves its dominant status over previously dominant fish by flashing their venomous caudal spine. The most dominant individuals often have the largest breeding territory. ("Palette surgeonfish", 2009; Froese and Pauly, 1991; Randall, 2001; "Blue Tang", 1999; "Blue Tang: Paracanthurus hepatus", 2010; Thresher, 1984)

When frightened, some common surgeon, particularly juveniles, hide behind live rocks or within branching corals. An alarmed fish secures its position within the head of the coral by extending its caudal spine into the coral. This prevents a predator from pulling the fish out of its hiding place, if found. If spotted by a predator, common surgeon "play dead", lying on their side, without any movement. They are often mistaken for dead and passed over by predators. In the aquarium trade, new enthusiasts worry that common surgeon have died when they play dead. However, within a few days of introduction to an aquarium, common surgeon become more comfortable with their environment and also often acquire dominant status. ("Palette surgeonfish", 2009; Froese and Pauly, 1991; Myers, 1991; "Blue Tang: Paracanthurus hepatus", 2010)

Home Range

The home range of common surgeon is often only defined during breeding. Home range varies depending on the dominance status of the fish as well as the method of breeding - paired or group broadcast spawning. (Randall, 2001; Thresher, 1984)

Communication and Perception

Common surgeon can communicate by changing their coloration. This color change depends on the conditions and how they perceive their environment. Under stress, for example, their blue coloration deepens. The black marks along the body may become bleached slightly and the markings less visible. The iridiphores causing the bright blue coloration appear smaller and less iridescent, hence the darker shade of blue. Other fish in the community can detect this color change and infer potential problems. Color change also occurs during stimulation such as male dominance interactions or breeding.

The coloration around the caudal spine serves as a warning to other species. In common surgeon, the yellow triangular coloration extends just beyond the caudal spine. In other species of surgeonfish, the location of the caudal spine may even be emphasized by a color that is not otherwise present on the body of the fish. (Goda and Fujii, 1998; Randall, 2001; Winterbottom, 1971)

  • Communication Channels
  • visual

Food Habits

Common surgeon are herbivorous. Unlike many marine fish, common surgeon rely only slightly on plankton. Instead, they graze on algae, using their small teeth to pull algae from rocks and coral. Fish of this species also feed on microalgae, other marine plants, and zooplankton. ("Palette surgeonfish", 2009; Froese and Pauly, 1991; "Blue Tang", 1999; "Blue Tang: Paracanthurus hepatus", 2010)


Common predators of common surgeon include tuna, bar jacks, and tiger groupers.

Common surgeon possess multiple anti-predator adaptations. Their razor-sharp caudal spine is venomous and can cause debilitating pain to small predators. The effectiveness of this defense mechanism is enhanced by the tendency of this species to congregate. If a predator were to attack a group of common surgeon, it would become surrounded by surgeonfish that were thrashing their tails and slashing with their protrusible caudal spines. Common surgeon also display bright aposematic coloration, warning predators of their poisonous skin and venomous spine.

Other species take advantage of these defense mechanisms. Midnight parrotfish, for example, display a similar blue coloration and join groups of common surgeon for protection. (Guiasu and Winterbottom, 1998; Randall, 2001; "Blue Tang", 1999)

Ecosystem Roles

Common surgeon feed largely on algae. Due to the small shape of their mouth, surgeonfish can easily pick and remove algae from uneven surfaces. Aggregations of common surgeon eat the fast growing algae from sponges in their habitat. This benefits the sponges and indirectly preserves habitat for species dependent on the steady growth of sponges. Midnight parrotfish mimic the coloration of common surgeon and often join their groups for protection.

If kept in an aquarium, common surgeon are vulnerable to many potentially lethal parasites. The most common of these is known as ich, paravortex, or marine spot disease, and is caused by the parasite, Cryptocaryon irritans. Ich causes dark spots along the sides of the fish, which may be difficult to detect against the dark blue coloration of this species. Common surgeon may be more prone to catching these types of diseases than other aquarium fish because they do not produce as much of the protective coating of slime as other species. (Randall, 2001; Shephard, 1994; "Blue Tang: Paracanthurus hepatus", 2010; Thresher, 1984)

  • Ecosystem Impact
  • creates habitat
Mutualist Species
Commensal/Parasitic Species
  • Cryptocaryon irritans

Economic Importance for Humans: Positive

Common surgeon are common in the pet trade. After the release of the movie, "Finding Nemo", popularity for the species increased. Also known as regal tang, blue tang, blue hippo tang or the blue or palette surgeonfish, this species retails from $30 to well over $100 USD for breeding pairs. ("Palette surgeonfish", 2009)

Economic Importance for Humans: Negative

The venomous caudal spine of common surgeon can inflict painful but minor wounds on humans. There are no other known adverse effects of common surgeon on humans. (Randall, 2001; "Blue Tang", 1999)

Conservation Status

Common surgeon have not been evaluated by the IUCN, the US Fish and Wildlife Service, or CITES. Nevertheless, human activities have negatively impacted the habitat of most coral reef inhabitants.

Common surgeon are popular in the aquarium trade, and have been harvested for this purpose for many years. Although overfishing has affected wild populations, common surgeon are not yet considered threatened. ("Palette surgeonfish", 2009; Froese and Pauly, 1991)

Other Comments

Paracanthurus hepatus is known by many common names such as common surgeon, blue hippo tang, regal tang and palette surgeonfish. They have recently become popular because of the popular animated movie, "Finding Nemo," in which a main character Dori, voiced by Ellen DeGeneres, is a common surgeon.


Anna Thurston (author), University of Michigan-Ann Arbor, Phil Myers (editor), University of Michigan-Ann Arbor, Gail McCormick (editor), Animal Diversity Web Staff.


Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map


having coloration that serves a protective function for the animal, usually used to refer to animals with colors that warn predators of their toxicity. For example: animals with bright red or yellow coloration are often toxic or distasteful.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


uses smells or other chemicals to communicate


particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body


union of egg and spermatozoan


An animal that eats mainly plants or parts of plants.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.


Having one mate at a time.


having the capacity to move from one place to another.


specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.


photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)


an animal which has a substance capable of killing, injuring, or impairing other animals through its chemical action (for example, the skin of poison dart frogs).


the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.


structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


lives alone


uses touch to communicate


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).


uses sight to communicate

year-round breeding

breeding takes place throughout the year


animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)


SeaWorld Parks & Entertainment. 1999. "Blue Tang" (On-line). SeaWorld/Busch Gardens ANIMALS. Accessed February 21, 2010 at

The Nature Conservancy. 2010. "Blue Tang: Paracanthurus hepatus" (On-line). Accessed April 10, 2010 at

Detroit Zoological Society. 2009. "Palette surgeonfish" (On-line). Detroit Zoo. Accessed February 20, 2010 at

Carpenter, K., V. Niem. 2001. "The Living Marine Resources of the Western Central Pacific" (On-line). Accessed February 21, 2010 at

Dunder, J. 2003. "Paracanthurus hepatus-Blue Hippo Tang or Regal Tang" (On-line). Accessed April 10, 2010 at

Fenner, B. 2010. "Paracanthurus hepatus" (On-line). Accessed February 20, 2010 at

Finacom, A., S. Linder, P. Schmidt. 2008. A View of the Philippine Coral Reef. San Francisco: California Academy of Sciences.

Froese, R., D. Pauly. 1991. "Paracanthurus Hepatus" (On-line). Encyclopedia of Life. Accessed February 20, 2010 at

Goda, M., R. Fujii. 1998. The Blue Coloration of the Common Surgeonfish, Paracanthurus hepatus—II. Zoological Science, 15(3): 323-333. Accessed March 17, 2010 at

Guiasu, R., R. Winterbottom. 1998. Yellow Juvenile Color Pattern, Diet Switching and the Phylogeny of the Surgeonfish Genus Zebrasoma (Percomorpha, Acanthuridae). Bulletin of Marine Science, 63/2: 277–294. Accessed February 21, 2010 at$File/Yellow%20juvenile%20color%20pattern.pdf?OpenElement.

Landeau, L., J. Terborgh. 1986. Oddity and the "Confusion Effect" in Predation. Animal Behaviour, 34/5: 1372-1380. Accessed April 02, 2010 at

Myers, R. 1991. "Palette surgeonfish" (On-line). Fish Base. Accessed February 20, 2010 at

Randall, J. 2001. Surgeonfishes of Hawai'i and the World. Honolulu, Hawai'i: Mutual Publishing.

Robertson, D. 1983. On the spawning behavior and spawning cycles of eight surgeonfishes (Acanthuridae) from the Indo-Pacific. Environmental Biology of Fishes, 9/3-4: 193-223. Accessed February 20, 2010 at

Ryan, S., K. Clarke. 2008. "Ecological assessment of the Queensland Marine Aquarium Fish Fishery" (On-line). Accessed February 21, 2010 at

Shephard, K. 1994. Functions for Fish Mucus. Reviews in Fish Biology and Fisheries, 4/4: 401-429. Accessed April 22, 2010 at

Thresher, R. 1984. Reproduction in Reef Fishes. Neptune City, NJ: T.F.H Publications, Inc. Ltd..

Waqalevu, V. 2009. "Capture, identification and culture techniques of coral reef fish and larvae" (On-line). Coral Reef Initiatives for the Pacific. Accessed April 02, 2010 at

Winterbottom, R. 1971. Movement of the Caudal Spine of Some Surgeonfishes. Copeia, 3: 562-566. Accessed March 17, 2010 at