[4] 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.

[1] 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.

[5] The juveniles occur in shallow sheltered areas, while adults show a preference for coastal reefs where there is rich coral growth which give the fish plenty of places to hide.

[1] Pomacanthus semicirculatus was first formally described as Holacanthus semicirculatus in 1831 by the French anatomist Georges Cuvier (1769–1832) with the type locality given as Timor, Bourou, Waigeo, Indonesia, and Port Praslin, New Ireland Island, Bismarck Archipelago in Papua New Guinea.