Semicircle Angelfish Identification Guide

Key identification features

• Large, deep-bodied angelfish reaching up to 40 cm
• Adults show a dark olive-green to brown body covered in fine, pale blue semicircular or scribbled lines
• Yellow-edged tail fin
• Blue markings forming a mask-like pattern around the eye
• Juveniles are strikingly different: jet-black body with tight, concentric pale blue and white rings
• Gradual transition through a mottled subadult phase as juvenile rings break up into adult scribbling

Common look-alikes

• Emperor Angelfish (Pomacanthus imperator): adults show straight horizontal yellow-and-blue stripes and a bold black eye mask rather than semicircular scribbled lines.
• Blue-ring Angelfish juveniles (Pomacanthus annularis): juvenile ring pattern is similar but the rings are more widely spaced and less tightly concentric than the Semicircle Angelfish juvenile.

Where you'll see one

This species ranges across the Indo-Pacific on lagoon and sheltered reef slopes rich in sponges and algae, with juveniles typically hiding in caves and under ledges before emerging onto open reef as they mature. Adults are generally solitary or found in loose pairs and can grow bold around divers on reefs where they are not disturbed.