Semicircle Angelfish

Pomacanthus semicirculatus, like other members of the genus Pomacanthus has adults and juveniles which are very different from each other. The adults are brownish green in colour with the scales edged in blue creating a blue speckling over the body and tail. All of the fins, apart from the plain yellow pectoral fins, have blue margins. There are long, filamentous growths from the dorsal and anal fins.

The juveniles in contrast, are blue-black marked from top to bottom with narrow white stripes. At the head end the stripes are fairly straight but they become increasingly curved as they approach the base of the tail. The juveniles gradually adopt the adult colouration when they are 8 to 16 centimetres (3.1 to 6.3 in). The dorsal fin contains 13 spines and 20–23 soft rays while the anal fin contains 3 spines and 18–22 soft rays. This species attains a maximum total length of 40 centimetres (16 in).

Pomacanthus semicirculatus is found in the Indo-Pacific region. Its range extends from the eastern coast of Africa from the southern Red Sea coast of Sudan south as far as South Africa. It then occurs east across the Indian and Pacific Oceans to Fiji, Tonga and Samoa.It occurs as far north as southern Japan and south to Australia. Within the Australian EEZ this species is widespread from the Houtman Abrolhos of Western Australia around the coast to as far south on the eastern coast as Sydney, juveniles extending farther south to Merimbula. It is also found at Christmas Island, the Cocos (Keeling) Islands as well as Lord Howe Island in the Tasman Sea. It has also been seen sporadically off the east coast of Florida since 1999 and at Oahu, Hawaii since 2005.