Acanthurus gahhm   (Forsskal,  1775) (Fish)
Organism information awaits expert curation
Class: Actinopterygii

Image copyrights: Field, R

Size: 34.3 cm.

Color: In preserved specimens lighter or darker brown. A dark brown bar or elongate patch from upper extremity of gill opening to above middle of pectoral. Caudal spine in a dark brown area, which is produced forward as a tapering band, reaching to above posterior or even anterior part of anal. Posterior part of caudal peduncle and base of caudal abruptly white, rest of caudal brown, with a broad white hind margin and a dark sub terminal one. Pectorals of the color of the body basally, then dark and then white at its distal third. Ventrals and anal of the color of the body, the anal with a narrow dark edge.

Height 2.1, 2.7-3 in length with caudal. Head 3.5-3.8, 4.6-5.4 in length with caudal. Eye 3.9-4.2, 2.9-3.2 in snout and 1.2-1.4 in snout and 1.2-1.4 in convex or very convex inter orbital space. Profile of head evenly convex from dorsal to tip of snout, much convex in large specimens. Corner of mouth to hind border of preopercle than to eye. Teeth rather slender, strongly lobated along the truncate tip and in smaller specimens also along the sides. Eight teeth in each ramus of both upper and lower jaw. Nostrils close together, near eye, with a low rim, that of the anterior nostril produced into a posterior flap. Origin of dorsal somewhat before or behind upper part of gill opening. A rather thick sheath covered with small elongate scales along the base of the fin. First dorsal spine very small, second twice as long as first, following gradually increasing in length to the last, which is much less than distance between corner of mouth and eye, and about 1.5 in snout. The anterior spine stronger than the posterior ones. Soft dorsal slightly higher than spinous part, rounded behind in young, pointed in adults. First anal spine minute, third longest, about equal to fifth dorsal spine. Soft anal similar to soft dorsal. Pectorals as long a or slightly longer than head. Ventrals pointed, much so in adults, slightly shorter than pectorals. Caudal lunate, the lobes produced and curved.

Remarks: Values in above description denote proportions.

Synonym (s)
Chaetodon nigricans Linnaeus, 1758
Chaetodon gahhm Forskal, 1775
Acanthurus gahm Cuvier and Valenciennes, 1835
Acanthurus gahhm Bleeker, 1858
Rhombotides gahhm Bleeker, 1865
Acanthurus gahm Klunzinger, 1871
Acanthurus gahm Gunther, 1875
Acanthurus (Rhombotides) gahm Klunzinger, 1884
Acanthurus gahm Sauvage, 1891
Acanthurus gahm Steindachner, 1901
Hepatus nigricans Jordan and Seale, 1906
Acanthurus gahm Herre, 1927, 1936
Hepatus nigricans Fowler and Bean, 1929
Acanthurus gahm var. nigricauda Duncker and Mohr, 1929

Common Name (s)
Economic Importance and Threats

Habitat:  Reef Associated
Trophic Level:  Secondary Consumer
Prey:  Plants, small animals, detritus


• Tamil Nadu, Gulf of Mannar INDIA

Literature Source(s)
  • Beaufort, LF and Chapman, WM (1951) The fishes of the Indo-Australian Archipelago A. J. Reprints agency, Karol Bagh, New Delhi 9 484 pp Available at - NIO, Goa
  • Society for the Management of European Biodiversity Data (2009) World Register of Marine Species (WoRMS) Available at -
  • Froese, R and Pauly, D (2000) Fishbase 2000: Concepts, design and data sources ICLARM 344 pp Available at -
  • Varghese, M; Manisseri, MK; Ramamurthy, N; Geetha, PM; Thomas, VJ and Gandhi, A (2011) Coral reef fishes of Gulf of Mannar, S.E of India Fishing Chimes CMFRI 31(1) 38-40 Available at - NIO, Goa

Page last updated on:2011-06-06

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