Family : Ostraciidae
Text © Giuseppe Mazza
English translation by Mario Beltramini
The Yellow boxfish (Ostracion cubicus Linnaeus, 1758) belongs to the class of Actinopterygii, the ray-finned fishes, to the order of the Tetraodontiformes and to the family of Ostraciidae known also as Coffer or Box fishes.
The name of the genus comes from the Greek “ostrakon” = shard, shell, with reference to the armour protecting it under the skin. The name of the species comes from the Latin “cubicus” = cubical, with reference to its shape.
It has a vey vast diffusion in the Indian and the Pacific Oceans. As an indication, we find it from South Africa and Madagascar to the Red Sea and the Arabic Sea, the Seychelles, Maldives, India, Sri Lanka, Thailand, Malaysia, Australia, Indonesia, New Guinea, Micronesia, New Caledonia, Philippines, Taiwan and China up to southern Japan. Eastwards, it reaches the Tonga, Samoa, Hawaii and Tuamotu islands; southwards, Lord Howe.
It lives in the madreporic formations up to about 300 m of depth; even if, usually, it keeps in the first 50 m.The adults mainly stay along the outer part of the reefs, the young in more sheltered positions, rich of caches, such as the madreporic formations of the genus Acropora.
The yellow boxfish has a body with squared section and can reach the 45 cm of length. Like all boxfishes, it has under the skin, a carapace, formed by hexagonal plates, with openings for the eyes, the mouth and the fins with the anal hole. The ventral fin is absent, and the locomotion is entrusted to the undulations of the dorsal and anal fins. The pectoral and the caudal ones are used as helms, for slow but precise manoeuvrings.
By sure, it is not a good swimmer and therefore it sails usually close to the bottom, where the currents are weaker.
The young, proportionally shorter than the adults, have a yellow livery, more or less pale, with black spots of the ocular diameter. Then, while growing, some white spots appear, surrounded by small black ones.
The yellow colour gets deeper in the females, whilst the males assume dark hues, often brown-greyish, with a thick black spotting, whilst the white spots and the fin colour of blue.When stressed, their skin may emit poisonous substances, which, in captivity, and if the pool is small, may kill the other fishes.
The Yellow boxfish is omnivorous. It nourishes of sea-weeds, foraminiferans, molluscs, sponges, ascidians, worms, crustaceans and small fishes.
It lives solitary or in small harems. This is usually one male with 2-4 females and the fecundated eggs are abandoned to the currents.
The populations may double in less than 15 months, and even if the young are often fished for the domestic aquaria, the vulnerability index of the species is very low: 23 per 100.
Ostracion argus Rüppell, 1828; Ostracion cubicum Linnaeus, 1758; Ostracion tuberculatus Linnaeus, 1758.