Campbell's Cardinalfish

A small pinkish cardinalfish of about 5 cm (2 in) with the oversized eye and blunt head typical of the family, and a dark spot at the base of the tail. It hangs motionless in caves and under overhangs through the day, in loose groups that scatter and re-form as a diver passes.

Cardinalfishes hunt at night, spreading out over sand and rubble for small crustaceans and then returning to the same shelter before dawn. The family's real distinction is what the males do with the eggs: the female passes the clutch to him and he holds it in his mouth until the young hatch, going without food for the whole period and rolling the mass periodically to keep it aerated. A brooding male is recognisable by a visibly distended throat and a reluctance to close his jaws, which is worth knowing before assuming a fish is deformed.