How to Identify Ocean Surgeonfish

To identify Ocean Surgeonfish (Acanthurus bahianus), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Adults typically exhibit a uniform grayish-brown to bluish-gray body coloration, often with a subtle iridescent sheen. The caudal fin is usually dark, sometimes with a pale posterior margin. Juveniles are often yellowish-brown, gradually transitioning to the adult coloration. Some individuals may display a pale bar or blotch behind the eye, which can be transient.

Scale type

ctenoid

Mouth position

terminal

Distinctive features

Scalpel-like spine on each side of the caudal peduncle (tail base), which is retractable and can be erected for defense., Small, terminal mouth with a single row of spatulate teeth adapted for grazing., Relatively small eyes positioned high on the head., Absence of prominent patterns or stripes on the body, distinguishing it from many other surgeonfish species.

Dorsal fin

Single, long dorsal fin with 9 dorsal spines and 23-26 soft rays.

Tail fin

Lunate (crescent-shaped) caudal fin.

Pectoral fin

Pectoral fins are relatively small and rounded, with 16-17 rays.

Distinctive fins

Anal fin with 3 spines and 21-23 soft rays. Pelvic fins with 1 spine and 5 soft rays.

Identification Tips

1. 1

   Body Coloration

   Look for the uniform grayish-brown to bluish-gray body. Juveniles are yellowish-brown.

2. 2

   Caudal Spine

   Observe the characteristic scalpel-like spine on the caudal peduncle. This is the defining feature of all surgeonfish.

3. 3

   Caudal Fin Shape

   Note the lunate (crescent-shaped) tail fin, which is typically dark.

4. 4

   Absence of Strong Patterns

   Distinguish it from other surgeonfish by its generally plain body coloration, lacking prominent stripes or spots.

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