Adults have an elongate white body with narrow chevron markings and may be up to 18 cm (7 in) in length. Juveniles have a mostly yellow tail and a broad black band extending from the rear of the dorsal fin to the rear of the anal fin. The tail pattern and the coloring of the posterior part of body changes dramatically with growth, with the tail entirely black with a thin yellow outline and the hind part of the body not differing in color from the areas further forward in adults. A juvenile Chevron butterflyfish, demonstrating the color difference compared to adult fish. With its peculiar age-dependent color and elongated outline, this species has been placed in a monotypic subgenus Megaprotodon. Its closest living relatives seem to be the species of the subgenera Discochaetodon (e.g. Eight-banded Butterflyfish, C. octofasciatus) and Tetrachaetodon (e.g. Mirror Butterflyfish, C. speculum). These, and perhaps other subgenera, would use Megaprotodon as genus name if Chaetodon is split up.
Chaetodon trifascialis is a territorial species which occurs in semi-protected seaward and shallow lagoon reefs, closely associated with tabular and staghorn (Acropora) corals, the polyps and mucus of which they eat. They occur at depths ranging from 2–30 m. Adults are either seen to swim alone or (particularly in the breeding season) in pairs, while juveniles are secretive among coral branches. They are oviparous.
corals polyps and mucus.
Chaetodon trifascialis is an obligate corallivore with a strong preference and apparent survival dependency (Berumen and Pratchett 2008) on Acropora hyacinthus but it has also been observed feeding on: A. intermedia (now recognized as A. nobilis and A. formosa), A. gemmifera, A. millepora, A. florida, A. cytherea, A. tenuis, A. robbusta, A. cerialis (Pratchett 2005), A. clathrata, P. damicornis (Graham 2007), A. aspera (Reese 1981), Stylophora pistillata, and Pocillopora eydouxi (Samways 2005). Most commonly occurs singly, sometimes also in pairs.
Chaetodon trifascialis is an obligate corallivore on a number of corals that are susceptible to bleaching events and have undergone population declines throughout the Indo-Pacific ranging from 20 to 37% because of reef loss and have been assessed under Red List Criteria (Carpenter et al. 2008). It has been observed feeding on: Acropora hyacinthus (with a strong preference and apparent survival dependency); A. intermedia (now recognized as A. nobilis and A. formosa); A. gemmifera; A. millepora; A. florida; A. cytherea; A. tenuis; A. robbusta; A. cerialis (Pratchett, 2005); A. clathrata; P. damicornis (Graham, 2007); A. aspera (Reese, 1981); Stylophora pistillata; and Pocillopora eydouxi (Samways, 2005). On reefs where it was observed in transects, it has been completely absent from transects after massive bleaching events (Pratchett et al. 2006).