The largest of the striped cardinalfishes, with visible canine teeth, and the male broods the eggs in his mouth.
The big one. Cardinalfishes are mostly small and this reaches about 25 cm, which on a muck site makes it the one hanging under the overhang rather than the one schooling over the coral head. The body is pale silver-brown with several dark horizontal stripes running from the snout to the tail, and the stripes fade with age, so a large adult can look almost plain with only a smudged remnant of the pattern.
The name to go by is the teeth. Cheilodipterus means split lip, and this species carries a pair of enlarged canines at the front of each jaw that are visible in a head-on photograph even with the mouth closed. Nothing else on the sand that looks like a cardinalfish has them. The two it is confused with are both in the same genus: the five-lined cardinalfish, which is far smaller and carries a clean black spot on the tail base ringed in yellow, and the wolf cardinalfish, whose stripes break up into dashes along the flank. Adults of this species keep the stripes continuous and lose the tail spot the smaller ones retain.
The male mouthbroods, and this is what the animal is worth photographing for. He takes the egg mass at spawning and holds it in the buccal cavity for the several days it takes to develop, and because the clutch is large relative to the head the jaw is visibly distended — the floor of the mouth bulges and the fish sits with the jaws slightly parted. Every so often he opens wide and churns the ball, which aerates it, and that is the frame worth waiting for. Late in the brood the embryos’ eyes show through the egg membranes as a mass of black points. He does not feed while he is carrying.
Mostly inactive by day, sheltering under ledges, inside wrecks and among jetty pilings, and out hunting small crustaceans and fish at night. A brooding male is easier to approach than an unencumbered one — he will not bolt far from the shelter — but he is also the one it is worst to harass, since a fish that panics can spit or swallow the clutch. A slow approach from a distance works, and the frame is worth leaving on once it is taken.
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.
