Blue Tang

Paracanthurus hepatus

Family: Acanthuridae | Genus: Paracanthurus

The blue tang (Paracanthurus hepatus) is a vibrant marine fish known for its deep indigo body, black banding, and bright yellow tail fin. It is one of the most iconic fish of tropical coral reefs, recognised by aquarists worldwide and famous for the sharp “scalpels” or spines on each side of its tail base, used defensively if threatened.

This species can grow up to 31 cm in length and live for around 20 years in its natural environment.

Geographical distribution

The blue tang inhabits the Indo-West Pacific region, from East Africa to Japan, Samoa, New Caledonia, and as far as the Great Barrier Reef in Australia. It lives in clear tropical waters, typically between 2 and 40 metres deep, although juveniles can often be found in shallower waters near branching corals.

Habitat

This species lives primarily in coastal coral reefs, characterised by:

Warm waters (23–27 °C) with a stable pH of 8.1–8.6.
Branching coral structures that provide shelter when threatened.
Typical depth: 2–40 m.
Moderate ocean currents that help distribute oxygen and nutrients.
Clear, tropical waters rich in macroalgae and zooplankton, which form its main food sources.

Lifestyle and behaviour

The blue tang is a social and generally peaceful species, though it can become aggressive in confined spaces.

Social behaviour :

Usually found in pairs or small groups but may also form large schools with other surgeonfish species.
Quickly seeks refuge among coral branches when threatened.
The intensity of its blue colour changes depending on stress levels or social interactions.

Daily activity:

Active and diurnal, spending the day feeding and swimming individually or in small shoals.

Reproduction:

Oviparous species with external fertilisation (broadcast spawning).
During spawning, males and females gather in groups and release gametes into the water column.
Eggs float and hatch within approximately 24 hours.
Larvae are pelagic, later settling on the reef as juveniles.
Males and females look alike, showing no clear sexual dimorphism; both may display colour changes during spawning.
Reproduction in captivity is extremely rare and challenging.
No parental care after spawning.

Other facts and curiosities:

Toxic to humans if eaten, as it can cause ciguatera poisoning.
Its blue pigmentation intensifies during stress or courtship, and fades when ill or frightened.
Possesses venomous spines at the base of the tail for defence, though it generally prefers to flee rather than fight.

Diet

In the wild

Juveniles: Feed mainly on plankton.
Adults: Omnivorous, with a diet dominated by macroalgae, zooplankton, marine algae, and other plant matter.

Under human care

Fed a varied commercial diet for omnivorous marine fish, including vegetables such as spinach, supplemented with frozen or freeze-dried animal proteins.
Requires a high proportion of plant-based food to maintain healthy metabolism and prevent common skin diseases.

Conservation status

The blue tang is listed as Least Concern (LC) on the IUCN Red List, with stable populations at present.
However, several potential threats could affect its survival:

Main threats:

Habitat loss due to coral reef degradation, driven by climate change, pollution, and ocean acidification