The ring-tailed cardinalfish (Ostorhinchus aureus) is a widespread fish species in the family Apogonidae found in the Red Sea and off East Africa to Papua New Guinea, north to Japan, and south to Australia.

[1] O. semilineatus O. gularis O. apogonoides O. aureus O. flagelliferus The French naturalist Philibert Commerson provided the first description of this fish from Réunion in the western Indian Ocean, but it was not published in a format allowing full citation.

The upper jaw has a narrow blue streak, and a broad blackish stripe extends from the front of the snout to the eye.

Easily confused with Ostorhinchus fleurieu,[8] where the black tail bar does not narrow in the centre, but unlike this species, the stripe is also present in juveniles.

Internally, O. aureus is one of a large group of nocturnal feeding fishes which has a black pigmented gut lining, apparently to hide the glow of bioluminescent prey from its own piscivores in turn.