Chelmon marginalis

Lore & Background

Chelmon marginalis is silvery white with two slender orange bars on the head and front part of the body, and a wide yellowish or yellowish-orange band close to the caudal peduncle. Adults lack a false eyespot or ocellus on the dorsal fin, but juveniles have a bar towards the tail and an ocellus on the dorsal fin that fade and disappear as the fish matures. The dorsal fin contains 9-10 spines and 29-33 soft rays, while the anal fin has 3 spines and 21-22 soft rays. This species attains a maximum total length of 18 centimetres (7.1 in).

It is endemic to Australia, found from the Houtman Abrolhos in Western Australia around the northern coasts to the northern Great Barrier Reef and reefs in the Coral Sea off Queensland. It inhabits coastal coral and rocky reefs, outer reef slopes, drop-offs, and areas around islands close to shore. A carnivorous species, it preys on benthic invertebrates such as crabs, shrimps, and polychaetes. Normally solitary, it forms pairs to breed, and breeding is oviparous.

The species was first formally described in 1842 by Scottish naval surgeon, arctic explorer, and naturalist Sir John Richardson, with the type locality given as Port Essington in the Northern Territory.

Reader's Guide

Chelmon marginalis is a species of butterflyfish endemic to Australia, with a distribution spanning from the Houtman Abrolhos in Western Australia around the northern coastline to the northern Great Barrier Reef and Coral Sea reefs. Its description by Sir John Richardson in 1842, based on a specimen from Port Essington, marks its formal entry into scientific literature. The species is characterized by its silvery white coloration with orange bars and a yellowish band, and the absence of a false eyespot in adults—a feature present in juveniles that fades with maturity. It reaches a maximum length of 18 cm and has specific fin ray counts. Ecologically, it is a carnivorous reef fish that feeds on benthic invertebrates and is typically solitary, pairing only for oviparous breeding. Despite its presence in Australian waters, it is rarely exported and uncommon in the aquarium trade, limiting its visibility outside its native range. The species' biology and distribution highlight its adaptation to coastal and outer reef environments, and its taxonomic history connects it to early 19th-century naturalist exploration in northern Australia.

Did You Know?

• Adults lack a false eyespot on the dorsal fin, but juveniles have an ocellus that fades as they mature.
• It was first formally described in 1842 by Sir John Richardson, with the type locality at Port Essington in the Northern Territory.
• This species is rarely exported and is uncommon in the aquarium trade.