Siganus trispilos

Lore & Background

Siganus trispilos was first formally described in 1977 by ichthyologists David J. Woodland and Gerald R. Allen, with the type locality given as off Tantabiddi Creek at the North West Cape in Western Australia. The specific name trispilos is a compound of tri meaning 'three' and spilos meaning 'mark' or 'spot', referencing the three large spots on the upper body.

The species has a laterally compressed deep body, with its depth fitting roughly twice into its standard length, and a deeply forked caudal fin. The forward nostril opening is a tube that expands to the rear into a wide flap, and there is a procumbent spine to the front of the dorsal fin. The fin spines hold venom glands. The overall colour is vivid yellow with three large dark brown blotches on the upper flanks, tiny bluish ocelli dotting the head, upper flanks, and lowest surface of the body, and an oblique, ill-defined brown stripe running through the eye.

Siganus trispilos is endemic to the eastern Indian Ocean off northwestern Western Australia, recorded from Ningaloo Reef to the Corneliesse Shoal northwest of Port Hedland. It inhabits areas rich in hard corals, particularly Acropora corals, where it lives as pairs browsing on upright seaweeds. If disturbed, the pairs dart into the coral for shelter. The venom in its fin spines is similar to that of stonefishes, as found in a study of a congener.

Reader's Guide

Siganus trispilos is significant as a narrowly endemic species restricted to a small portion of the eastern Indian Ocean off northwestern Western Australia. Its description in 1977 by Woodland and Allen added to the known diversity of rabbitfishes in the region. The species' reliance on hard coral habitats, especially Acropora, ties its conservation to the health of coral reefs. Its venomous fin spines, similar to those of stonefishes, highlight a defensive adaptation shared among rabbitfishes. The three large dark blotches that give it its common names make it visually distinctive among siganids. As a pair-living, coral-dwelling herbivore that browses on upright seaweeds, it plays a role in the reef ecosystem. Its limited distribution and specific habitat requirements make it a species of interest for regional biodiversity studies and reef management.

Did You Know?

• Its specific name trispilos means 'three mark' in reference to the three large spots on its upper body.
• This species attains a maximum total length of 33.5 cm (13.2 in).