Widespread tropical Western Pacific, from Japan to Australia, ranging west to Thailand, Christmas Island and Western Australia and east to Coral Sea and New South Wales. Expatriates south to Montague Island and coastal waters of southern New South Wales. Often a common species found in various habitats from silty coastal bays and harbours to outer reefs. Adults occur in small loose groups where common. Small juveniles secretive in narrow crevices, often where sea-urchins rest during the day. Adults and juveniles are readily identified by their mostly black colour and a conspicuous white vertical bar or blotch centrally on the body . In tiny juveniles it is usually present us a narrow bar from top to bottom, shortening and widening proportionally with growth. First a yellow border on the anal fin develops with growth and then a narrow blue line between the black and yellow, that lines up with the blue margins of the caudal and dorsal fins appears. Some large individuals are black with a blue hue, probably males. Length to 15cm.