Its skin secretes a soapy toxin that will kill everything else in a bucket with it, and its larva trails two long dorsal streamers.
A yellow fish with two dark bars, one through the eye and one across the middle of the body, and a compressed, deep shape that lets it hang almost motionless beside a coral head. It hunts small fish by drifting up beside something larger and using it as cover, which is worth watching for once you know to look.
The soap is real. The skin secretes grammistin, a bitter proteinaceous toxin that foams in water. An aquarist who stresses one in a small tank can lose the tank. It is not a diving hazard in any practical sense — you would have to pick the fish up — but it is why nothing eats them and why they can afford to be conspicuous.
The blackwater stage is the reason this entry sits in this group. The postlarva carries the second dorsal spine drawn out into a long trailing filament, sometimes two, several times the length of the body, and swims in open water at night before settling onto the reef. It looks like an entirely different animal and is a common blackwater subject.
WoRMS treats Diploprion bifasciatum, the spelling in most field guides, as an incorrect original spelling and gives D. bifasciatus. That is the spelling used here.
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.
