Semicircle Angelfish

Overview

The Semicircle Angelfish (Pomacanthus semicirculatus) is a striking marine species known for its dramatic transformation from juvenile to adult coloration. Typically found in tropical waters, this fish is recognized by its deep, laterally compressed body and elegant swimming style.

Distribution & Habitat

This species is widely distributed across the Indo-West Pacific, ranging from the Red Sea and East Africa to Fiji, and from southern Japan down to New South Wales and Lord Howe Island. Juveniles are commonly found in shallow, protected areas such as rock pools and crevices, while adults prefer coastal reefs with abundant coral growth, caves, and overhangs where they can find shelter.

Appearance

Adults display a greenish-yellow or brownish body covered in fine blue spots, with blue margins on their fins and gill covers. A notable feature is the presence of long, trailing filaments on the dorsal and anal fins. In contrast, juveniles are dark blue-black with distinct, concentric white and blue semi-circular stripes that radiate toward the tail. The transition between these two color phases typically occurs as the fish grows between 8 and 16 cm in length.

Biology & Behavior

These fish are generally solitary or found in pairs and are known to be diurnal. They possess a sharp spine on each gill cover, which serves as a defense mechanism against predators and helps them wedge securely into reef crevices. When threatened, they may produce audible grunting sounds.

Feeding

As an omnivorous species, the Semicircle Angelfish feeds on a varied diet in the wild, primarily consisting of sponges, tunicates, and benthic algae.