Chaetodon trifascialis is one of 88 members of the genus Chaetodon, which together with 11 additional genera make up the butterflyfishes family (Chaetodontidae) in which a total of 129 species are currently described. This species is distributed over a wide area comprising the Indian and Pacific Oceans, from the east coast of Africa, covering the entire Indian Ocean and in the Pacific as far as the Line Islands and Australia. It inhabits the semi-protected waters of the seagrass meadows as well as shallow lagoons, usually in places with large presence of corals of the genus Acropora, and up to depths of 30 meters.
The body of Chaetodon trifascialis is relatively elongated, triangular in shape and laterally compressed. The rostrum ends in a short and robust snout, with a small mouth located at the end. They can grow up to 18 cm in total length. The dorsal fin consists of 13-15 spines with strongly indented interspinal membranes, followed by 14-16 soft rays. The anal fin has 3-5 spines and 13-15 soft rays. The posterior ends of the dorsal and anal fins form an angle from which the fins are almost vertical until they reach the caudal peduncle. The caudal fin is truncated in shape.
The color of the caudal fin of Chaetodon trifascialis is black with a yellow posterior margin. There is a black band with pale edges running through the eye. The dorsal and anal fin are yellowish with electric blue edges. The flank of the specimens of this species have thin stripes that from the center of the body are directed in opposite directions, those directed upwards with respect to those below. In the central part, these lines intersect. Juveniles have a black vertical band running from the back of the dorsal fin, over the back of the body to the back of the anal fins and have yellow tail base and pectoral fins.
Adult specimens of Chaetodon trifascialis are usually solitary or form pairs during the breeding season. The diet of this species is based on the polyps of the Acropora corals among which they shelter, as well as the mucus generated by these corals.
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