About Siganus spinus (Linnaeus, 1758)
Siganus spinus has a laterally compressed, deep, relatively slender body, where its body depth is 2.3 to 2.8 times its standard length. The dorsal profile of the head is indented above the eye, and the snout is convex and blunt. The front nostril has a long flap that extends at least two-thirds of the way to the rear nostril. A recumbent spine sits in front of the dorsal fin. Like all rabbitfishes, the dorsal fin has 13 spines and 10 soft rays, while the anal fin has 7 spines and 9 soft rays. The fin spines contain venom glands. The caudal fin is emarginate in juveniles and truncate in adults. This species reaches a maximum total length of 28 cm (11 in), with 18 cm (7.1 in) being a more typical length. Its body is covered in a labyrinthine pattern of thin brown markings, with mottled fins, and 4 to 5 irregular light-coloured bars are frequently present on the caudal peduncle. The body pattern extends onto the pelvic fins and the spiny sections of the dorsal and anal fins. The soft rays of the dorsal and anal fins each have 2 to 3 dark bands and hyaline membranes. There are 4 pale bars on the caudal fin, though these are often ill-defined except on the outer rays. The pectoral fins are hyaline. Siganus spinus has a wide distribution across the Indo-Pacific, ranging from India and Sri Lanka east to the Tuamotu Islands, north to Japan, and south to New Caledonia. In Australia, it occurs from Carnarvon to Exmouth Gulf in Western Australia, along the northern Great Barrier Reef and Torres Strait south to Moreton Bay in Queensland, and also lives in the Coral Sea. It inhabits depths between 1 and 50 m (3 ft 3 in and 164 ft 1 in). Adult Siganus spinus are found on shallow coral reef flats and can also occur in rivers. Juveniles aggregate in large groups around corals that have algae growing at their bases.
