Almost black with a fine white line at the base of the dorsal and anal fins, feeding up in the water off drop-offs.
To 25 cm, which is half the size of the black durgon and is itself a useful separator. Dark: bluish or violet in life and near-black in poor light.
The identification is the fin margins. This species has a narrow but clear white edge around the tail, and white edging on the dorsal and anal fins. The black durgon has its white line at the fin bases, where the fins meet the body, not at the edges. Base against edge is the check, and size and behaviour back it up: this fish is usually alone, where the black durgon aggregates.
It lives on coral-rich seaward slopes between 1 and 30 m and feeds on sponges, algae, crustaceans and small invertebrates. The range is the Indian Ocean from the Red Sea and East Africa east to western Thailand and Indonesia, and it is well recorded through the Maldive atolls. It is harmless.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.