Dark Surgeonfish, Acanthurus blochii Valenciennes 1835

Other Names: Dark Surgeon, Ringtail Surgeonfish

A Dark Surgeonfish, Acanthurus blochii, on the Ribbon Reefs, Great Barier Reef, Queensland, October 2005. Source: Erik Schlogl / iNaturalist.org. License: CC by Attribution-NonCommercial

A bluish-grey to dark brown surgeonfish with numerous small yellowish-brown spots forming irregular longitudinal lines, often a white bar around caudal-fin base, narrow irregular stripes in head, a small yellow to orange spot behind the eye, and a narrow blue margin on the dorsal, anal caudal fins.
This species may be misidentified as Acanthurus mata.

Cite this page as:
Bray, D.J. 2017, Acanthurus blochii in Fishes of Australia, accessed 17 Jul 2024, https://fishesofaustralia.net.au/Home/species/1022

Dark Surgeonfish, Acanthurus blochii Valenciennes 1835

More Info


Offshore reefs of Western Australia (Rowley Shoals to Scott Reef), Ashmore Reef, Timor Sea, and the northern Great Barrier Reef, Queensland and reefs in the Coral Sea, to Narooma, New South Wales; also Lord Howe Island in the Tasman Sea, and Cocos (Keeling) Islands and Christmas Island in the eastern Indian Ocean. Elsewhere, the species is widespread in the Indo-west-central Pacific from East Africa to the Hawaiian Islands.
Inhabits outer lagoon and seaward reefs, usually in small groups and sin schools at some oceanic locations.


Dorsal fin IX, 25-27; Anal fin III, 24-25. Caudal spine large, 3 - 4.4 in head length. Stomach gizzard-like.


Rowley Shoals (17°20'S) to Scott Reef (14°03'S), WA and Ashmore Reef, Timor Sea (12°15'S), Christmas Island and Cocos (Keeling) Islands, and northern Great Barrier Reef, QLD (12°00'S) to Merimbula, NSW (36°55'S), also Coringa-Herald Cay and Lihou Reef, Coral Sea, Elizabeth and Middleton Reefs and Lord Howe Island; tropical, Indo-west-central Pacific.


Bluish grey with numerous yellowish brown spots which tend to form irregular longitudinal lines; head with narrow irregular stripes; behind eye a yellow spot; brown pectoral fins; base of caudal fin with white bar. The pale ring around the tail base varies in intensity and may occasionally be absent.


Grazer/detrivore  - feeds mostly on algal film covering compacted sand, also on diatoms and detritus.


Targeted as a food fish in parts of its range, and also collected for the aquarium industry.

Similar Species

Differs from Acanthurus dussumieri in having vertical stripes vs. spots on the blue central area of the caudal fin; from A. mata in having a lunate caudal fin; from A. xanthopterus in having plain brown to bluish-grey pectoral fins.

Species Citation

Acanthurus blochii Valenciennes in Cuvier, & Valenciennes 1835, Histoire Naturelle des Poissons 10: 209. Type locality: Mauritius and Seychelles.


Bray, D.J. 2017


Australian Faunal Directory

Dark Surgeonfish, Acanthurus blochii Valenciennes 1835


Allen, G.R. 1993. Fishes of Ashmore Reef and Cartier Island. Records of the Western Australian Museum, Supplement 44: 67-91.

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

Allen, G.R. & Russell, B.C. 1986. Fishes of Rowley Shoals - Scott Reef. Records of the Western Australian Museum Supplement 25: 75-103.

Allen, G.R. & Smith-Vaniz, W.F. 1994. Fishes of Cocos (Keeling) Islands. Atoll Research Bulletin 412: 1-21.

Allen, G.R., Steene, R.C. & Orchard, M. 2007. Fishes of Christmas Island. Christmas Island : Christmas Island Natural History Association 2 edn, 284 pp.

Choat, J.H., Abesamis, R., Clements, K.D., McIlwain, J., Myers, R., Nanola, C., Rocha, L.A., Russell, B. & Stockwell, B. 2012. Acanthurus blochii. The IUCN Red List of Threatened Species 2012: e.T177971A1507181. http://dx.doi.org/10.2305/IUCN.UK.2012.RLTS.T177971A1507181.en . Downloaded on 21 October 2015.

Choat, J.H., Robbins, W.D. & Clements, K.D. 2004. The trophic status of herbivorous fishes on coral reefs. Marine Biology 145: 445-454.

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Francis, M. 1993. Checklist of the coastal fishes of Lord Howe, Norfolk, and Kermadec Islands, southwest Pacific Ocean. Pacific Science 47(2): 136-170 figs 1-2

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Kuiter, R.H. 1992. Tropical Reef-Fishes of the Western Pacific, Indonesia and Adjacent Waters. Jakarta : PT Gramedia Pustaka Utama 314 pp. pls. 

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Oxley, W.G., Ayling, A.M., Cheal, A.J. & Osborne, K. 2004. Marine surveys undertaken in the Elizabeth and Middleton Reefs Marine National Nature Reserve, December 2003. Townsville : Australian Institute of Marine Sciences 64 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.

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

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Russell, B.C., Larson, H.K., Hutchins, J.B. & Allen, G.R. 2005. Reef fishes of the Sahul Shelf. The Beagle, Records of the Museums and Art Galleries of the Northern Territory Supplement 1 2005: 83-105

Quick Facts

CAAB Code:37437007

Behaviour:2-15 m

Conservation:IUCN Least Concern

Fishing:Aquarium fish

Habitat:Reef associated

Max Size:45 cm SL

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Species Maps

CAAB distribution map