A slender grouper that behaves like nothing of the kind, feeding on plankton in aggregations of hundreds in open water.
To about 35 cm. It does not read as a grouper at first glance: small head, short snout, forked tail, and a habit of hanging in open water. Greenish-brown above and reddish below, with five white or blue-white spots along the back, a bright blue spot in the pectoral armpit, and two or three more blue or violet spots on the upper body. Juveniles are bright yellow or grey with five dark spots along the back.
The row of pale spots along the back plus the blue armpit spot is what to look for; the other silvery fish hanging in the same water is the scissortail damselfish, which has neither.
It forms large midwater schools above rock, picking individual zooplankton out of the water — the short snout gives it close-range binocular vision — and it drops back into the reef when threatened, which is the behaviour a diver triggers by swimming at it.
Ten to seventy metres by one source and nought to a hundred and twenty by another. Sex change and cleaning behaviour are unrecorded. The genus is unsettled: FishBase and STRI use Cephalopholis colonus, while much of the diving literature uses Paranthias colonus.
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.
