Juveniles move as one dense ball that rolls over the sand like a single animal.
An eel-tailed catfish to about 32 cm, dark brown to black with two clean cream stripes running the length of the body, four pairs of barbels around the mouth, and a continuous fin running around the tail. Adults are solitary or in small loose groups and are usually seen at night. Juveniles are the reason the species is photographed.
Young fish form tight balls of dozens to hundreds of individuals that move as a single mass, rolling and turning over the sediment while the fish at the front feed and those at the back swim over the top — a continuous churning motion that is easier to recognise than to describe. The ball is a defence, and it holds together under a diver’s light. The first dorsal and both pectoral spines are venomous and the sting is severe, so the ball is photographed rather than parted. Recorded from the shallows to about 30 m, usually near a piling, wreck or rubble patch rather than on open sand.
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.