How to Identify Brown Surgeonfish

To identify Brown Surgeonfish (Acanthurus nigrofuscus), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Adults are typically uniform brown to purplish-brown, often with a yellowish wash on the head and anterior body. A prominent black spot is present at the posterior end of the dorsal fin base, and another smaller black spot at the posterior end of the anal fin base. The caudal fin is often dark, sometimes with a pale posterior margin. Juveniles are generally lighter brown or yellowish.

Scale type

ctenoid

Mouth position

terminal

Distinctive features

Two distinct black spots: one at the posterior base of the dorsal fin and another at the posterior base of the anal fin., Small, dark spots or lines on the head and anterior body, especially noticeable in some individuals., A sharp, retractable scalpel-like spine on each side of the caudal peduncle.

Dorsal fin

Single dorsal fin with IX spines and 23-25 soft rays. The spinous and soft-rayed portions are continuous.

Tail fin

Lunate (crescent-shaped) caudal fin.

Pectoral fin

16-17 rays, relatively large and fan-like.

Distinctive fins

Pelvic fins with I spine and 3 soft rays. Anal fin with III spines and 21-23 soft rays.

Identification Tips

1. 1

   Coloration

   Look for the overall brown to purplish-brown body color. The yellowish wash on the head is often a good indicator.

2. 2

   Black Spots

   The two distinct black spots, one at the base of the dorsal fin and one at the base of the anal fin, are the most reliable distinguishing features.

3. 3

   Caudal Fin

   Observe the lunate (crescent-shaped) caudal fin, which is typically dark, sometimes with a pale posterior margin.

4. 4

   Size

   Adults typically reach a maximum standard length of about 25 cm (10 inches).

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