Chaetodon trifasciatus is one of the 88 members belonging to the genus Chaetodon, which together with 11 additional genera make up the butterflyfishes family (Chaetodontidae) in which there are currently a total of 129 described species. It is a species that is distributed throughout the Indian Ocean, and until recently it was believed that it was also present in the Pacific Ocean, although recently it has been considered that in the latter territory the species is another, Chaetodon lunulatus. Chaetodon trifasciatus is associated with coral reefs at depths of up to 20 meters, although there are records of specimens found at depths of up to 1,000 meters.
The body of Chaetodon trifasciatus is oval and laterally compressed, like most members of its family. They can reach up to 15 cm in maximum total length. The rostrum is flat, with a small terminal mouth and concave cephalic profiles. It has 13 to 14 spines on the dorsal fin, with indented interspinal membranes, and 20 to 22 soft rays posteriorly. The anal fin has 3 spines and 18-21 soft rays. The caudal fin is rounded.
The general body coloration of Chaetodon trifasciatus is light pink dorsally, fading to yellow towards the belly. Several diagonal, almost horizontal, blue-purple stripes run across the body. The pectoral and pelvic fins are yellow. The dorsal, anal and caudal fins have a thick black line with a yellow margin. On the margin of the anal fin, it has a reddish-brown stripe. The head is also yellow, with the black stripe across the eye, so characteristic of the genus, which in its case has a yellow margin. The mouth is black.
It looks very similar to Chaetodon lunulatus, so much so that they seem completely identical. The only difference that will allow us to differentiate them is that in the case of Chaetodon trifasciatus the anterior part of the caudal fin is orange-yellow, while in Chaetodon lunulatus this part is bluish-white. Another differentiating feature are the black stripes that cross their eyes, since in the case of Chaetodon trifasciatus these stripes do not reach the upper edge of the head, while in Chaetodon lunulatus they do.
The feeding of Chaetodon trifasciatus is exclusively formed by corals, with a strong preference for those of the genus Pocillopora. During the day the specimens feed among the corals, and during the night they seek shelter in them.
Chaetodon trifasciatus is a dioecious species, or of separate sexes, oviparous, and of external fertilization. Spawning occurs before dusk. They form pairs during maturation that will last for their entire lives.
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