Heniochus chrysostomus, common name Threeband pennantfish, is a tropical fish of the family Chaetodontidae. Heniochus chrysostomus can attain a maximum length of 18 centimetres (7.1 in) in males. The body is oval, laterally flattened, with a basic white color and three broad oblique brown bands. The first band runs from the forehead up to the pelvic fins, the second from the dorsal fin to the anal fin, the third is adjacent to the dorsal fin. The dorsal fin is elongated, in juveniles much more than in adults. Juvenile fishes are solitary. The snout tip is yellow. This species is oviparous and feeds on coral polyps. This species has an Indo-Pacific distribution, from Western India to Pitcairn Islands, Japan, southern Queensland, Micronesia and New Caledonia. Threeband pennantfish typically lives below the intertidal zone in coastal waters and in shallow water lagoon among the coral reefs, at a depth of 2–40 metres (6 ft 7 in–131 ft 3 in).