A dark damselfish that develops a raised forehead with age, on shallow rock in the surge zone.
To about 31 cm on one figure and 38 on another. The adult has a pronounced bump on the forehead and angular tips to the dorsal, anal and tail fins. The juvenile is a different animal: bright blue over the upper half of the head and body, orange over the lower half.
The giant damselfish is fully sympatric with it and the forehead settles it — present here, absent there.
One to ten metres on rocky inshore reef exposed to wave action and current. Mainly a herbivore. Eggs are laid in rock crevices in strong current, on the sheltered side, and the male guards and fans them. Whether it defends its territory against divers, as its congener does, is not recorded.
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.