Acanthurus nigricans   (Linnaeus,  1758) (Fish)
Organism information awaits expert curation
Class: Actinopterygii

Image copyrights: Randall, J.E.

Size: Max length 21.3 cm TL (male/unsexed)

Color: Dark brown with an elongate black bar from behind upper edge of gill opening to above middle of pectoral. Groove of caudal spine black with the black tapering stripe extending forward on side. Dorsal and anal dark brown with a narrow black edge. Caudal lighter to dark brown with a whitish hind margin. Posterior part of caudal peduncle and base of caudal abruptly white in small specimens. Pectoral dark brown, hind border broadly whitish. Ventral dark brown, inner rays sometimes lighter basally.

Head 3.4-3.8 in standard length, 4.6-5.3 in total length. Depth of body 2.0-2.3 in standard length, 2.6-3.1 in total length. Eye diameter 3.9-4.3 in head, 2.3-2.6 in snout and 1.3-1.5 in highly convex interorbital space. Corner of mouth nearer to hind border of preopercle than to eye. Eight lobate teeth on each side of both jaws. First dorsal spine very small, second about as long as the first, subsequent spines increasing in length, 7th to 9th subequal, about twice eye diameter. First anal spine short, 3rd longer than 2nd and slightly shorter than longest dorsal spines. Pectoral fin equal to length of head, ventral shorter than pectoral. Caudal fin lunate, the lobes produced.
Number of spines and rays in the dorsal fin: IX, 26-28; number of spines and rays in the anal fin: III, 24-26; number of rays in the pectoral fin: ii, 14-15; number of spines and rays in the ventral fin: I, 5; number of scale rows along the lateral line: 138-145; number of horizontal scale rows usually counted from origin of the dorsal fin to the lateral line and from anal origin to the lateral line: 13-14+62-70.

Dioecious, external fertilization, nonguarders, open water/substratum egg scatterers. Monogamous.

Remarks: Values in above description denote proportions.

Synonym (s)
Acanthurus aliala Lesson, 1831
(Junior synonym)
Acanthurus glaucopareius Cuvier, 1829
(Junior synonym)
Acanthurus japonicus (non Schmidt, 1930)
(Misapplied name)
Acanthurus nigricans (Linnaeus, 1758)
(Senior synonym)
Chaetodon nigricans Linnaeus, 1758
(Senior synonym)
Chaetodon nigricans Linnaeus, 1758
Acanthurus gahhm de Beaufort, 1951
Acanthurus gahm Smith and Smith, 1963
Acanthurus nigricans Jones, 1969
Acanthurus glaucoparecius Cuvier, 1829

Common Name (s)
• Rykathi (Mahl)
• Pala (Malayalam)
Economic Importance and Threats
Importance:  Commercial
(Fisheries, aquarium)

Habitat:  Bentho Pelagic, Reef Associated
Trophic Level:  Primary Consumer
Prey:  Filamentous algae


• Lakshadweep, Agatti INDIA
• Lakshadweep, Amini INDIA
• Lakshadweep, Kavaratti INDIA
• Lakshadweep, Minicoy INDIA
• Lakshadweep INDIA
• Red Sea

Literature Source(s)
  • Wafar, MVM (2003) Checklists of reef fauna Available at -
  • UNEP World Conservation Monitoring Centre Available at -
  • Rouphael, T; Turak, E and Jon, B Seagrasses and mangroves of Yemen's Red Sea 41-89
  • Allen, GR and Mohammed, A (2003) Coral Reef Fishes of Indonesia Zoological Studies 42(1) 26299 Available at - Digital Information Resource Center, Pune.
  • Jones, S and Kumaran, M (1980) Fishes of the Laccadive Archipelago The Nature Conservation and Aquatic Sciences Service, Trivandrum, Kerala 760 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 -
  • Jones, S. (1969) Catalogue of fishes from the Laccadive Archipelago in the reference collections of the Central Marine Fisheries Research Institute. Bulletin of Central Marine Research Institute CMFRI, Cochin 8 1-35 Available at -

Page last updated on:2011-03-10

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