Blue surgeonfish characteristics, habitat, classification, behavior

Egbert Haynes

The blue surgeonfish (Paracanthurus hepatus) is part of the Acanthuridae family. Its most outstanding characteristic is the coloration of its body, being in the adult stage a bright blue color.

On this tonality, a particular oval black spot stands out, which extends from the base of the eye to the caudal end. The tail has a luminous yellow hue, a color that is also present on the tips of the pectoral fins and on the lower part of the belly..

Blue surgeonfish. Source: Tewy [CC BY-SA (]

In relation to the fins, they are formed by sharp spines and soft rays. If the fish feels threatened, it spreads the spines located on the caudal peduncle, in order to protect itself from the predator. However, in this same situation, he could lie on his side without moving, pretending that he is dead..

The distribution of this marine species is wide, located in the waters of the Indian and Pacific oceans. As for the habitat, it prefers coral reefs, where it can take shelter, thus escaping from predators. In addition, these coral formations are an abundant source of algae, an important part of their diet..

Article index

  • 1 Communication
  • 2 General characteristics
    • 2.1 Fins
    • 2.2 iridophores
    • 2.3 Coloring
  • 3 Conservation status
    • 3.1 - Threats
    • 3.2 - Conservation actions
  • 4 Habitat and distribution
    • 4.1 Habitat
  • 5 Taxonomy and classification
  • 6 Food
  • 7 Playback
    • 7.1 The hatchlings
  • 8 Behavior
  • 9 References 


The blue surgeonfish can communicate with its conspecifices, changing their color. This temporary variation in the tones of their body is associated with the conditions and the way they perceive the environment. For example, if you are stressed, the blue color becomes darker.

In addition, the black spot that it has along the body fades slightly and the rest of the marks become less visible..

Specialists point out that these variations are related to iridophores. These diminish its ability to be iridescent, causing the luminous blue color to become deeper..

In this way, the rest of the fish can detect color changes and interpret them as an alarm signal, in the event of a threat. Also, color changes occur during male interactions for dominance establishment and during reproduction..

On the other hand, the bright yellow color of the tail fin is a warning notice for other species..

General characteristics

The blue surgeonfish has a flat body, laterally compressed and rounded in shape. In general, the female is smaller than the male. Thus, body length can vary from 12 to 38 centimeters, although the average ranges between 25 and 31 centimeters. Regarding the weight, it is approximately 600 grams.

The muzzle is pointed, ending in a small mouth. It has tiny, curved and fine teeth. In relation to the eyes, they are located at the top of the head.


This species has some peculiarities in its fins, which identify and differentiate it from the rest of its class. One of these are the sharp thorns that make them up.

The dorsal fin is large and continuous. It is made up of 9 spines, followed by 19 to 20 soft rays. The anal has a symmetrical structure, presenting 3 spines and between 18 and 19 soft rays.

As for the pelvic fins, they are small and have 1 spiny radius and 3 flexible ones. The pectorals are wide and have a rounded tip. These have a total of 16 radios.

The Paracanthurus hepatus it has a very sharp caudal spine, located at the base of the tail. This rests in an indentation that the fish has, under the epidermis. Its base is attached by a ligament to the vertebrae of the spine. This allows the spine to move freely, thanks to the contraction of the muscles..

When the animal feels threatened, this structure extends. Thus, in the event that the predator tries to capture it, it pierces the skin and inoculates the toxins it contains..


Iridophores are specialized static cells found in blue surgeonfish skin, especially on light surfaces..

In their cytoplasm they contain numerous refractory flat crystals, which are responsible for reflecting light. Said crystalline plates are arranged in a parallel manner, maintaining uniform distances from each other..

When the sheets are illuminated by outside light, iridescent colors, green and cobalt blue are generated. This occurs due to the diffraction of light rays as they pass through the plates.


The shades of the blue surgeonfish vary according to their stage of development. Thus, the young are bright yellow, with some blue spots in the area near the eyes. The dorsal and anal fins are light blue.

Once adult, the Paracanthurus hepatus It is characterized by a vibrant sky blue coloration. The adult has a thick, oval, dark spot that starts from the eye and extends to the tail, where it turns almost black..

This stripe has a light blue patch, just behind the pectoral fin. Some species show a fluorescent greenish yellow belly

The caudal fin has a large yellow triangle, the smallest vertex of which is at the base of it. As for the pectoral fin, it is the same color as the body, but exhibits a bright yellow spot on its end..

State of conservation

Blue surgeonfish populations are declining, mainly due to water pollution. This situation has caused IUCN to include the Paracanthurus hepatus within the group of animals that make up the red list of species at risk of extinction.

Although this body considers that it is within a low range of extinction, it considers it necessary to solve the problems that afflict it. On the contrary, the problem would become more acute, thus increasing the risk of disappearing as a species..

- Threats

Coral reef degradation

Coral reefs are among the preferred habitats for this fish. These are seriously affected by environmental pollution, overfishing, ocean acidification and global warming..

According to a United Nations report, almost 70% of the coral reefs that exist on Earth are threatened. Of these, 20% cannot be recovered, 24% are under imminent risk and the remaining 26% could present long-term problems.

H5 Problem

Corals try to counteract the action of pollutants. However, this process produces what is known as coral bleaching, where they lose their bright colors and turn white..

In this state, these plant species are no longer active contributors to reef biodiversity. This is due to its important function as a source of food and as a protection for young and young..

In addition, the alteration of this ecosystem affects the seagrasses, where this species also inhabits. Another problem that affects coral reefs is sedimentation. When solid waste reaches bodies of water, it is deposited to the bottom, thus blocking light and preventing photosynthesis.


In various areas of its distribution, overexploitation constitutes a great threat. The capture of this fish is carried out in order to be used as bait for fishing and to be sold in aquarium shops.

To capture it and sell it as a pet, man uses cyanide. This substance stuns the fish and facilitates its capture. However, it is a highly polluting technique for the environment.

- Conservation actions

At present there are no concrete measures aimed at conserving the Paracanthurus hepatus. However, its range of distribution is superimposed on several marine regions that are protected..

Habitat and distribution

The blue surgeonfish is widely distributed in the Pacific and Indian oceans, excluding the Red Sea. In this way, it inhabits between latitudes 30 ° N, 30 ° S and 32 ° E, and at 170 ° W. Thus, it extends from Africa to the Lina Islands, Micronesia and the Samoa Islands..

To the north, it covers as far as Kochi Prefecture, located on the island of Shikoku, Japan. Regarding its location to the south, it lives up to New South Wales, in Australia. Two cases have been reported on the island of Hawaii, but experts consider them to be the product of releases from aquariums.


The Paracanthurus hepatus It is a marine animal found in subtropical and tropical coastal areas, where water temperatures are between 24 and 26 ° C. The vast majority of species inhabit coral reefs, especially near the Pocillopora eydouxi.

This coral is characterized by having branched extensions, which serve the fish to hide from predators. In addition to this, the reefs provide plant material that serves as food, such as algae..

In addition to these ecosystems, blue surgeonfish can live in mangroves, sea beds, rocky reefs, and beds of algae. Thus, the animal is able to remain in epipelagic depths of 2 to 40 meters. Also, it can develop in channels, where there is a moderate to strong water current..

Taxonomy and classification

-Animal Kingdom.

-Subkingdom: Bilateria

-Phylum: Chordate.

-Subfilum: Vertebrate.

-Infrafilum: Gnathostomata.

-Superclass: Actinopterygii.

-Class: Teleostei.

-Superorder: Acanthopterygii.

-Order: Perciformes.

-Suborder: Acanthuroidei.

-Family: Acanthuridae.

-Genus: Paracanthurus.

-Species: Paracanthurus hepatus.


The diet of the blue surgeonfish varies according to its stage of development. In the larval stage, it can feed on ciliates (Euplotes sp.), rotifers (Brachionus rotundiformis) and copepods (Parvocalanus crassirostris).

According to research conducted at the University of Florida, among these three species, larvae show a preference for rotifers. This occurs regardless of the abundance that exists in the environment of each of these dams..

On the other hand, the young are herbivores, feeding mainly on plankton. However, they frequently eat algae, which they extract from corals and rocks using their tiny teeth. When the Paracanthurus hepatus he is an adult, he has an omnivorous diet. Thus, it eats algae and zooplankton, such as small shrimp and krill.


Sexual maturity in this species is related to its size. Thus, the male can reproduce when it measures around 11 centimeters, while the female does so when it reaches 13 centimeters in length..

The blue surgeonfish spontaneously form breeding groups. These dissolve and regroup several times, before spawning occurs. Males tend to court females aggressively, often ending in a spawning race to the surface..

As they swiftly swim upward, the females shed about 40,000 eggs, and the males release sperm. These fish are diffusion reproducers, since sperm and eggs are released directly into the water, so fertilization is carried out externally..

Specialists state that the accelerated swimming rhythm during spawning allows the dispersal and mixing of the male and female gametes. Regarding the hatching of the eggs, it occurs 24 to 26 hours after they have been fertilized.

The babies

The larvae are born underdeveloped and feed on the egg yolk. They can float, but remain at rest for up to 5 hours after hatching. Two days later, the development of the fins begins, so the larvae begin to make short movements.

Later, the growth of the intestines and jaws begins and on the seventh day the scales are formed. After 37 days, the larvae have fully matured.


Often the Paracanthurus hepatus It is usually seen swimming alone. However, most of the time you are in pairs or in small groups.

The male may have aggressive encounters with other males. In these violent behaviors, they surround each other and show their caudal column. In addition, the blue tone that characterizes them varies, as the intensity of the fight increases..

The males try to attack each other with the spines, for which they swim close, until the tail fin can come into contact with the opponent's body, to injure it..

The display of this caudal spine can have a great influence on the social position of the fish. In this way, the dominant of the group has a greater territory of reproduction..

When the blue surgeonfish is scared, it hides behind branching corals or rocks. The animal hides its head in the coral, spreading the tail spine at the same time. In this way, the predator cannot capture it.


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