Emerges from rubble at dusk to mate, which is the only reliable time to see one.
Small, to about 7 cm, and unmistakable — a psychedelic green ground overlaid with orange and blue vermiculate banding. The only real confusion is with the picturesque dragonet, which carries ocellate blotches rather than continuous bands. It has no scales; instead it produces a thick, bitter, foul-smelling mucus. The blue is worth a sentence because it is genuinely unusual: most blue in animals is structural, made by the way light scatters off tissue, but this fish has a true blue pigment held in cells called cyanophores, along with dichromatic chromatophores carrying both blue and red pigment in one cell. Pigmentary blue of this kind is known from almost nowhere else in the vertebrates.
The mating ascent is the reason people dive at dusk for it, and it has been properly studied rather than merely described. Spawning happens within twenty minutes of sunset. The window across a whole population averages under half an hour, and actual gamete release is confined to about four and a half minutes of it. A pair rises slowly together, for seven to twelve seconds, releases eggs and sperm at the top and drops back to the rubble. Males are polygynous and mate repeatedly; a female spawns once in an evening or not at all; larger males do better. The eggs are pelagic. This is a fish of sheltered lagoons and inshore reefs on silty bottoms with rubble and coral, between about 1 and 18 m, living in small groups over a small patch — which is why a guide can take you back to the same colony on consecutive evenings.
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.