How to Identify Blue Tang

To identify Blue Tang (Acanthurus coeruleus), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Adults are typically a vibrant royal blue, often with a yellow caudal fin. Juveniles are bright yellow with blue-tipped fins, gradually transitioning to blue as they mature. Some individuals may display a darker blue or purplish hue, especially when stressed or at night. A dark spot may be present at the base of the pectoral fin. The color can change rapidly depending on mood, stress, or time of day.

Scale type

ctenoid

Mouth position

terminal

Distinctive features

Laterally compressed, oval-shaped body, Small, terminal mouth, Scalpel-like spine on each side of the caudal peduncle (tail base), Continuous dorsal fin, Bright blue coloration in adults, yellow in juveniles

Dorsal fin

Single, long dorsal fin with 9 dorsal spines and 23-25 dorsal soft rays.

Tail fin

Lunate (crescent-shaped) caudal fin, often yellow in adults.

Pectoral fin

Large, fan-like pectoral fins with 16-17 rays.

Distinctive fins

Anal fin with 3 spines and 21-23 soft rays. Pelvic fins with 1 spine and 3 soft rays. The caudal peduncle bears a sharp, retractable spine on each side.

Identification Tips

1. 1

   Coloration

   Adults are uniformly royal blue with a yellow caudal fin. Juveniles are entirely bright yellow with blue fin margins. This ontogenetic color change is a key identifier.

2. 2

   Body Shape

   Laterally compressed, disc-shaped body, typical of surgeonfish.

3. 3

   Caudal Spine

   Presence of a sharp, retractable scalpel-like spine on each side of the caudal peduncle. This is a defining characteristic of all surgeonfish (family Acanthuridae).

4. 4

   Mouth

   Small, downturned mouth adapted for grazing algae.

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