Silverblotched Unicornfish, Naso caesius Randall & Bell 1992

Other Names: Gray Unicornfish, Grey Unicornfish, Silver-blotched Unicorn

A Silverblotched Unicornfish, Naso caesius, at Eniwetak Atoll, Marshall Islands. Source: John E. Randall / FishBase. License: CC by Attribution-NonCommercial

A bluish-grey to dark brownish-grey surgeonfish with a bluish tail, and sometimes irregular vertical lighter or darker blotches on the sides.
The two keel-like spines on the elliptical bony plates on each side of caudal peduncle, are semicircular to subquadrangular when viewed from above (not sharply pointed with the tip projecting forward, as in Naso hexacanthus).

Cite this page as:
Bray, D.J. 2022, Naso caesius in Fishes of Australia, accessed 16 Apr 2024,

Silverblotched Unicornfish, Naso caesius Randall & Bell 1992

More Info


Off shore reefs of north Western Australia, Ashmore Reef in the Timor Sea, and the northern Great Barrier Reef, Queensland, and reefs in the Coral Sea, to the Kurnell Peninsula, New South Wales, and the Lord Howe Province in the Tasman Sea; also Cocos (Keeling) Islands and Christmas Island in the eastern Indian Ocean. Elsewhere the species occurs in the tropical, west-central Pacific.
Inhabits clear oceanic waters along steep dropoffs, offshore reefs and pinnacles.


Dorsal fin VI-VII, 27-30; Anal fin II, 28-31; Pectoral fin 16-18, the upper two rays unbranched; Pelvic fin I, 3; Caudal fin (branched rays) 14; Gill rakers 3-5 + 8-11).
Two elliptical bony plates on each side of caudal peduncle, each with a keel-like spine projecting laterally in adults, more in males than females; shape of peduncular spines semicircular to subquadrangular when viewed from above (not sharply pointed with the tip projecting forward.


Bluish grey, paler ventrally (almost white on some individuals); able to rapidly change to a pattern of vertically elongate blotches on about upper two-thirds of body, which may be either darker or paler than the ground colour (many blotches approximately elliptical, some irregular, and some interconnected); three pale bands may be present on head, one horizontal at level of upper edge of eye, and two diagonal on cheek; caudal fin more blue than body, without any distinct posterior border of different colour; pectoral rays somewhat yellowish. An occasional colour phase, also rapidly attained, is overall dark greyish-brown.


This species is easily confused with Naso hexacanthus, and some records may be misidentified as N. hexacanthus.

Similar Species

Differs from the similar Naso hexcanthus in having smaller bladelike caudal spines that do not become sharply pointed and antrorse in large males, a pale tongue (vs. black in N. hexacanthus), overall bluish grey (vs. yellowish ventrally in N. hexacanthus), in lacking dark borders on the opercle and preopercle (present in N. hexacanthus).


The specific name is from the Latin caesius (= bluish-grey) in reference to the overall colour of this species.

Species Citation

Naso caesius Randall & Bell, 1992, Pacific Science 46(3): 347, pl. IA-B, fig. 2. Type locality: Marshall Islands, Enewetak Atoll, north side of East Channel (main pass of the atoll) at wreck of concrete ship, 3-5 m.


Bray, D.J. 2022


Atlas of Living Australia

Silverblotched Unicornfish, Naso caesius Randall & Bell 1992


Allen, G.R. & Erdmann, M.V. 2012. Reef fishes of the East Indies. Perth : Tropical Reef Research 3 vols, 1260 pp.

Borden, W.C. 1998. Phylogeny of the unicornfishes (Naso, Acanthuridae) based on soft anatomy. Copeia 1998(1): 104-113.

Choat, J.H., Abesamis, R., Clements, K.D., McIlwain, J., Myers, R., Nanola, C., Rocha, L.A., Russell, B. & Stockwell, B. 2012. Naso caesius. The IUCN Red List of Threatened Species 2012: e.T178013A1521341. Downloaded on 22 February 2019.

Dayton, C., Santayana, A.C.  & Lacson, J.M. 1994. Genetic evidence for reproductive isolation of the recently described unicornfish Naso caesius and its sibling N. hexacanthus. Marine Biology 118: 551-554.

Hobbs, J-P.A., Ayling, A.M., Choat, J.H., Gilligan, J.J., McDonald, C.A., Neilson, J. & Newman, S.J. 2010. New records of marine fishes illustrate the biogeographic importance of Christmas Island, Indian Ocean. Zootaxa 2422: 63–68.

Kuiter, R.H. & Debelius, H. 2001. Surgeonfishes, Rabbitfishes and Their Relatives. A comprehensive guide to Acanthuroidei. Chorleywood, U.K. : TMC Publishing 208 pp.

Myers, R.F. 1999. Micronesian Reef Fishes. A comprehensive guide to the coral reef fishes of Micronesia. Guam : Coral Graphics vi 330 pp. 

Oxley, W.G., Ayling, A.M., Cheal, A.J. & Thompson, A.A. 2003. Marine surveys undertaken in the Coringa-Herald National Nature Reserve, March-April 2003. Townsville : Australian Institute of Marine Science 59 pp.

Oxley, W.G., Emslie, M., Muir, P. & Thompson, A.A. 2004. Marine surveys undertaken in the Lihou Reef National Nature Reserve, March 2004. Townsville : Australian Institute of Marine Science i-vii, 1-67 pp.

Randall, J.E. 2001. Surgeonfishes of Hawai'i and the World. Honolulu : Mutual Publishing and Bishop Museum Press 125 pp. 

Randall, J.E. 2001. Zanclidae, Acanthuridae. pp. 3651-3683 in Carpenter, K.E. & Niem, T.H. (eds). The Living Marine Resources of the Western Central Pacific. FAO Species Identification Guide for Fisheries Purposes. Rome : FAO Vol. 6 pp. 3381-4218.

Randall, J.E. 2005. Reef and shore fishes of the South Pacific. New Caledonia to Tahiti and the Pitcairn Islands. Honolulu : University of Hawaii Press 707 pp.

Randall, J.E., Allen, G.R. & Steene, R. 1990. Fishes of the Great Barrier Reef and Coral Sea. Bathurst : Crawford House Press 507 pp. (as Naso thorpei

Randall, J.E., Allen, G.R. & Steene, R. 1997. Fishes of the Great Barrier Reef and Coral Sea. Bathurst : Crawford House Press 557 pp. figs.

Randall, J.E. & Bell, L.J. 1992. Naso caesius, a new acanthurid fish from the Central Pacific. Pacific Science 46(3): 344-352. See ref online

Quick Facts

CAAB Code:37437046

Conservation:IUCN Least Concern

Depth:15-50 m

Habitat:Reef associated

Max Size:63 cm TL

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CAAB distribution map