Semicircle angelfish
A marine angelfish with distinct juvenile and adult colouration.
The semicircle angelfish, also called the Koran, blue, zebra, or half-circled angelfish, is a marine ray-finned fish belonging to the family Pomacanthidae. It lives in the Indo-West Pacific Ocean and sometimes appears in the aquarium trade.
Like other members of the genus *Pomacanthus*, the adults and juveniles look completely different. Adults are brownish-green with blue-edged scales that create a speckled pattern across the body and tail. All fins except the plain yellow pectoral fins have blue margins, and the dorsal and anal fins grow long, filamentous extensions. Juveniles, on the other hand, are blue-black with narrow white stripes running from top to bottom. The stripes near the head are fairly straight but become increasingly curved toward the tail base. Juveniles gradually shift to adult coloration when they reach 8 to 16 centimeters (3.1 to 6.3 inches) in length. The dorsal fin has 13 spines and 20 to 23 soft rays, while the anal fin has 3 spines and 18 to 22 soft rays. The maximum total length is 40 centimeters (16 inches).
This species ranges across the Indo-Pacific, from the eastern coast of Africa—starting near the southern Red Sea coast of Sudan and extending south to South Africa—then east across the Indian and Pacific Oceans to Fiji, Tonga, and Samoa. It reaches as far north as southern Japan and south to Australia. Within Australian waters, it is widespread from the Houtman Abrolhos in Western Australia around the coast to Sydney on the eastern side, with juveniles extending farther south to Merimbula. It also occurs at Christmas Island, the Cocos (Keeling) Islands, and Lord Howe Island in the Tasman Sea. Since 1999, it has been spotted sporadically off Florida’s east coast, and since 2005 at Oahu, Hawaii.
The fish lives at depths of 1 to 40 meters (3 feet 3 inches to 131 feet 3 inches) on sheltered coral reefs, feeding on algae, tunicates, and sponges. Juveniles are timid and hard to approach, staying in shallow sheltered areas. Adults prefer coastal reefs with rich coral growth that offers plenty of hiding spots, and they are usually seen alone or in pairs. Adults have also been recorded from shipwrecks.
Quick Facts
- Taxon
- Pomacanthus semicirculatus
Facts from the source article.
Lore & Background
Pomacanthus semicirculatus was first formally described as Holacanthus semicirculatus in 1831 by the French anatomist Georges Cuvier, with type localities including Timor, Bourou, Waigeo, Indonesia, and Port Praslin, New Ireland Island, Bismarck Archipelago in Papua New Guinea. The specific name semicirculatus means 'semicircular', referring to the semicircular slender blue and white lines on the rear of the body on juveniles, which are lost on the adults. Some authorities place this species in the subgenus Arusetta.
Adults are brownish green with scales edged in blue, creating a blue speckling over the body and tail. All fins except the plain yellow pectoral fins have blue margins, and there are long, filamentous growths from the dorsal and anal fins. Juveniles are blue-black with narrow white stripes that are straight at the head end and become increasingly curved toward the base of the tail. Juveniles gradually adopt adult colouration when they are 8 to 16 centimetres long.
The species is found in the Indo-Pacific region, from the eastern coast of Africa (southern Red Sea coast of Sudan to South Africa) east across the Indian and Pacific Oceans to Fiji, Tonga and Samoa, north to southern Japan, and south to Australia. Within Australian waters it occurs from the Houtman Abrolhos of Western Australia around the coast to as far south on the eastern coast as Sydney, with juveniles extending farther south to Merimbula. It is also found at Christmas Island, the Cocos (Keeling) Islands, and Lord Howe Island. It has been seen sporadically off the east coast of Florida since 1999 and at Oahu, Hawaii since 2005.
Reader's Guide
Pomacanthus semicirculatus is notable for its striking difference between juvenile and adult colouration, a characteristic shared with other members of the genus Pomacanthus. The species is found at depths between 1 and 40 metres on sheltered coral reefs, where it feeds on algae, tunicates and sponges. Juveniles are very timid and difficult to approach, occurring in shallow sheltered areas, while adults prefer coastal reefs with rich coral growth that provide hiding places. Adults are typically encountered in pairs or as solitary individuals and have been recorded from wrecks. The species is frequently encountered in the aquarium trade, contributing to its recognition among marine fish enthusiasts. Its wide distribution across the Indo-West Pacific, from eastern Africa to the Pacific islands, and its sporadic appearances in Florida and Hawaii, underscore its adaptability and the interest it generates in both natural and captive settings.
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