How to Identify Bluehead Wrasse

To identify Bluehead Wrasse (Thalassoma bifasciatum), look at these key features.

Physical Characteristics

Body shape

elongated

Coloration

Highly variable depending on sex and phase. Initial Phase (IP) individuals (females and small males) are typically yellow or white with a dark lateral stripe, often with a dark spot at the base of the caudal fin. Terminal Phase (TP) males are strikingly colored with a bright blue head, two prominent black vertical bars behind the pectoral fin, and a green body that fades to blue or yellow posteriorly. The caudal fin is often lunate with elongated lobes in TP males.

Scale type

cycloid

Mouth position

terminal

Distinctive features

Pronounced sexual dimorphism and dichromatism, Distinctive blue head and black bars in terminal phase males, Lunate caudal fin in terminal phase males, Small, pointed snout

Dorsal fin

Single dorsal fin with 8 spines and 13 soft rays, continuous and relatively low.

Tail fin

Caudal fin is truncate to slightly emarginate in initial phase, becoming distinctly lunate with elongated upper and lower lobes in terminal phase males.

Pectoral fin

Large, fan-like pectoral fins, typically with 13 rays.

Distinctive fins

Pelvic fins are small and located thoracically.

Identification Tips

1. 1

   Terminal Phase (TP) Male

   Look for the bright blue head, two prominent black vertical bars on the body just behind the pectoral fins, and a green to greenish-blue body. The caudal fin is typically lunate with elongated lobes.

2. 2

   Initial Phase (IP) Female/Juvenile

   These are generally smaller, with a yellow or white body, often a dark lateral stripe running from the snout to the caudal peduncle, and sometimes a dark spot at the base of the caudal fin. They lack the blue head and black bars of the TP male.

3. 3

   Size

   Adults typically reach up to 15-20 cm (6-8 inches) in total length, with TP males generally being larger.

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