Scribbled Rabbitfish

Siganus spinus has a laterally compressed, deep and relatively slender body which has a depth which fits into its standard length 2.3 to 2.8 times. The dorsal profile of the head is indented above eye, the snout is convex and blunt. The front nostril has a long flap which reaches to at least two-thirds of the way to the rear nostril. There is a recumbent spine 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 hold venom glands. The caudal fin is emarginate in juveniles and truncate in adults. This species attains a maximum total length of 28 cm (11 in), although 18 cm (7.1 in) is more typical. The body is covered in a labyrinthine pattern of thin brown markings with mottled fins and frequently 4-5 irregular light-coloured bars on the caudal peduncle. The pattern on the body reaches onto the pelvic fins and spiny parts of the dorsal and anal fins. The soft rays of the dorsal and anal fins each have 2-3 dark bands and hyaline membranes. There are 4 pale bars on the caudal fin, but these are frequently ill-defined other than on the outer rays. The pectoral fins are hyaline.

Siganus spinus has a wide Indo-Pacific range, extending from India and Sri Lanka eastwards to the Tuamotu Islands, northwards to Japan and south as far as New Caledonia. In Australia this species is found from Carnarvon to Exmouth Gulf in Western Australia and along the northern Great Barrier Reef and the Torres Strait south to Moreton Bay in Queensland, also in the Coral Sea. It is found at depths between 1 and 50 m (3 ft 3 in and 164 ft 1 in). Adults are found in shallow coral reef flats and can also occur in rivers. The juveniles aggregate in larger numbers in corals which have algae growing at their bases.