Dark blue in mid-water over drop-offs, in numbers, with red teeth visible up close.
To about 40 cm, dark blue-green to purple-black with pale lines running back from the snout, a deeply forked tail with the lobes drawn into filaments, and red-pink teeth that are visible at close range. Colour intensity varies with mood and depth, and a fish in a current can look almost black.
It is the most planktivorous of the triggerfishes, feeding in mid-water above drop-offs in aggregations of tens to hundreds where current concentrates food, and dropping into holes in the reef when threatened. It is not territorial towards divers away from a nest and is easily approached in the open, though it keeps a steady distance. Recorded from about 5 to 40 m and much more numerous where there is current.
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.