Bluetail trunkfish (Ostracion cyanurus)

Classification (WoRMS)

Full classification as recorded by WoRMS: Kingdom: Animalia · Phylum: Chordata · Class: Teleostei · Order: Tetraodontiformes · Family: Ostraciidae · Genus: Ostracion.

Accepted name: Ostracion cyanurus · Authority: Rüppell, 1828 · Taxonomic status: accepted · AphiaID: 219909.

Source: World Register of Marine Species (WoRMS) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=219909 (CC BY 4.0). Accessed 2026-09-23.

Biology and life history (FishBase)

Measured values published by FishBase for Ostracion cyanurus. Only fields the database actually holds for this species are shown; these are database values, not aquarium guidance.

Maximum length: 15 cm · Habitat zone: reef-associated · Body shape: fusiform / normal · Vulnerability index: 10 of 100 · Aquarium trade: never/rarely.

FishBase notes: Inhabits areas of moderate coral growth (Ref. 9710). Solitary and found close to shelter (Ref. 9710).

Source: FishBase species summary (SpecCode 12743) — https://www.fishbase.se/summary/Ostracion-cyanurus.html (CC BY-NC 3.0 — non-commercial use only). Accessed 2026-09-23.

Distribution and occurrence records (GBIF)

445 georeferenced occurrence records for Ostracion cyanurus are published through GBIF from 12 countries or marine areas. The map above plots 53 distinct locations from a sample of 445 records, omitting 9 inland records that carry an institution's coordinates rather than a collection site; it shows where the species has been observed and reported, not a modelled range.

Most records by country or area: Egypt (270); Oman (57); Saudi Arabia (40); United Arab Emirates (25); Israel (22); Jordan (12); Eritrea (6); Micronesia (Federated States of) (5); Sudan (3); Yemen (3); Bahrain (1); Iran (Islamic Republic of) (1).

Marine regions with a valid WoRMS distribution record: Red Sea.

Source: GBIF Occurrence Search (taxonKey 5213778) — https://www.gbif.org/occurrence/search?taxon_key=5213778&has_coordinate=true (records CC0 / CC BY); WoRMS distribution records (MarineRegions) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=219909 (CC BY 4.0); Natural Earth 110m basemap — https://www.naturalearthdata.com/ (public domain). Accessed 2026-09-23.

Conservation status (IUCN Red List)

The IUCN Red List assesses Ostracion cyanurum Rüppell, 1828 as Least Concern (code LC). No trend, population estimate or threat analysis is given here, because none is available from this source without the Red List API; follow the source link for the full assessment, including its date.

Source: IUCN Red List of Threatened Species (taxon 193627) — https://www.iucnredlist.org/species/193627/0; GBIF IUCN Red List category endpoint (taxonKey 5213778) — https://api.gbif.org/v1/species/5213778/iucnRedListCategory. Accessed 2026-09-23.

Description and natural history (Wikipedia)

Ostracion cyanurus was first formally described in 1828 by the German naturalist and explorer Eduard Rüppell with its type locality given as the Red Sea off Al Muwaylih in Tabuk Province, Saudi Arabia. The bluetail trunkfish is classified in the genus Ostracion which the 5th edition of Fishes of the World classifies within the family Ostraciidae in the suborder Ostracioidea within the order Tetraodontiformes.

Ostracion cyanurus is classified in the genus Ostracion, this name means "little box" and is an allusion to the shape of the body of its type species, O. cubicum. The specific name, cyanurus means "blue tail" and is a reference to the blue caudal fin of this fish. Ostracion is neuter so it has been argued that the specific name should be spelt as cyanurum.

Ostracion cyanurus has a maximum published total length of 15 cm. There are 9 soft rays on both the dorsal and anal fin, and 10 in the caudal fin, with 8 branched. Females have a slightly concave dorsal profile of the head while that of males is convex. The lips and chin are fleshy and stick out. The adult males are normally dark blue on the flanks and lower body with spots and an unspotted greenish-yellow upper body. Females are yellow with blue spots and red cheeks.

Ostracion cyanurus is found in the Western Indian Ocean where it occurs in the Red Sea and around the Arabian Peninsula into the Persian Gulf as far east as eastern Iran. This species is found in areas where there is a moderate growth of coral at depths between 5 and 50 m.

Ostracion cyanurus is a solitary species which remains in the vicinity of shelter. The apparent lack of smaller males may mean that this species is protogynous. If the bluetail trunkfish senses danger is releases a toxin called pahutoxin, or ostracotoxin, into the water as a defence.

Ostracion cyanurus is available in the aquarium trade.

Source: Wikipedia: Ostracion cyanurus — https://en.wikipedia.org/wiki/Ostracion_cyanurus (CC BY-SA 4.0). Accessed 2026-09-23.