How to Identify Orange-shoulder Surgeonfish

To identify Orange-shoulder Surgeonfish (Acanthurus olivaceus), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Adults typically display a brownish-grey to dark olive body, often with a pale anterior body and a darker posterior. A prominent, elongated orange patch is located behind the upper operculum, extending onto the shoulder. The dorsal and anal fins are often edged in blue. Juveniles are bright yellow with a small, dark spot at the base of the pectoral fin, gradually transitioning to adult coloration as they mature.

Scale type

ctenoid

Mouth position

terminal

Distinctive features

Sharp, retractable scalpel-like spine on each side of the caudal peduncle., Distinctive orange shoulder patch in adults., Bright yellow juvenile coloration.

Dorsal fin

Dorsal fin with 9 spines and 23-25 soft rays, continuous and relatively long.

Tail fin

Lunate (crescent-shaped) caudal fin.

Pectoral fin

Pectoral fins are clear to yellowish, with 16-17 rays.

Distinctive fins

Anal fin with 3 spines and 22-24 soft rays. Pelvic fins with 1 spine and 5 soft rays.

Identification Tips

1. 1

   Adult Coloration

   Look for the brownish-grey to olive body with the prominent orange patch behind the operculum. The anterior body is often lighter than the posterior.

2. 2

   Juvenile Coloration

   Bright yellow body with a small, dark spot at the base of the pectoral fin. This is a key identifier for juveniles.

3. 3

   Caudal Spine

   Observe the characteristic scalpel-like spine on the caudal peduncle, typical of all surgeonfish.

4. 4

   Body Shape

   Laterally compressed, oval body shape.

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