Family : Chaetodontidae
Text © Giuseppe Mazza
English translation by Mario Beltramini
The Indian butterflyfish (Chaetodon mitratus Günther, 1860) belongs to the class of the Actinopterygii, the ray-finned fishes, to the order of the Perciformes and to the family of the Chaetodontidae.
The name of the genus Chaetodon comes from the Greek “χαίτη” (khaite) = hair and “ὀδούς” (odous) = tooth, because of the teeth shaped like bristles, whilst tha specific one, mitratus, in Latin with the mitre, with the turban, refers to the dark oblique bands over the head.
The Chaetodon mitratus is present only in nine sites of the Indian Ocean. We find it along the coasts of Madagascar and adjacent islands of Comoros, Mautitius, Réunion, Seychelles, then proceeding eastwards in the Maldives and Chagos islands, and then finally in the Cocos and Christmas islands.
It lives in relatively deep waters for a butterfly fish, usually at 50-68 m, where grow, on the outer slopes of the reefs, the gorgonians and the black corals. It can go down up to 80 m and is rarely found over the 40 m with some exceptional ascension to the 22 m.
It measures less than 13 cm with a maximum of 16 cm. The body, as normal among the Chaetodon, is laterally flat with the tall back, but here, unlike usual, the profile is more triangular than oval and the snout is short. The mouth is protractile with 6-7 rows of tiny teeth arranged like brushes on both jaws. The background colour is yellow, more intense in the specimens of the Mauritius, with 3 characteristic bands. The first, vertical, camouflages the eye and the other two, wider and oblique, wrap the body, including the first part of the dorsal fin that, when it is really cornered and cannot escape, the fish raises against the enemies, with 8 spiny rays and 18-20 soft, to scare them and to look bigger. The remaining part of the dorsal fin has orange shades and the tiny border is white. All other fins, but the trasnparent pectorals, are yellow. The anal has 3 spiny rays and 14-15 soft; the pectoral and pelvic ones are unarmed; the caudal is more or less truncated.
The Chaetodon mitratus nourishes of plankton and small benthic invertebrates. It lives alone or in small groups of 5 individuals at the most. During the reproductive period couples, at times lasting, take form.
The mating takes place while swimming and the eggs, fecundated on the flight by the male, are entrusted to the currents. They hatch on the following day. The pelagic larvae go drifting for about 2 months and the small fishes reach often the bottoms very far away from the place where they were born. Once reached a certain size, the juvenile livery is practically the same as the adults one.
It is a relatively long-lived species, sold at high price for the aquarium life. The populations can double in less than 15 months and the vulnerability index is therefore nowadays (2020) very low, marking only 13 on a scale of 100.
Tetragonoptrus mitratus (Günther, 1860).