Surf parrotfish

Siganus rivulatus has a laterally compressed body which has a standard length of 2.7-3.4 times its depth The dorsal fin has 13 spines and 10 soft rays, the anal fin has 7 spines and 9 soft rays, there are 23 vertebrae and the caudal fin is forked. The longest spine in the dorsal fin is shorter than the distance between the eye and the edge of the operculum while the length of the snout is equal to or greater the length of the snout. The slender spines are barbed and bear venom. The teeth are incisor-like with lateral cusps and are arranged in a single row in the jaws. The body is covered in small embedded scales, except of the midline of the underside. The colour is variable and it usually shows some darks spots and yellow wavy lines along the sides. The upper body tends to be grey-green to brown with a yellow abdomen or silvery white underside. It usually grows to around 10–20 cm, sometimes up to 27 cm in standard length but the maximum recorded size is 40 cm.