Ring-tailed cardinalfish
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. Taxonomy. 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. Therefore, the species name and description by Bernard Germain de Lacépède (who acknowledged Commerson) takes precedence, albeit with a nod to Commerson. With no original or subsequent illustrations or specimens denoted  as types, Fricke nominated a neotype in 1999 but subsequently withdrew it. Etymology. This species has on occasion been mistakenly considered a junior synonym of the similar species "Ostorhinchus fleurieu", but is generally acknowledged as separate; it had the junior species synonym "roseipinnis" applied by Georges Cuvier in 1829. Lacépède coined the genus "Ostorhinchus" in 1802 to which "O. aureus" was eventually assigned, although he originally placed it in the genus "Centropomus" which is now placed in a different fish family, Centropomidae. Description. This fish is coppery-coloured with a broad blackish bar at the base of the tail, up  to 14.5 cm in length. 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", 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. The eyes of "O. aureus" allow the transmission of ultraviolet light , which if it is proven to be able to see, could benefit its nocturnal foraging. Meristics. Using a shorthand meristics formula, "O. aureus" can be described as having: D, VII-I,9 A, II,8 P, 14 LL, 25 GR, 6-8 + 16-20 Habitat. "Ostorhinchus aureus" inhabits holes in rocks or under ledges in shallow waters. It is known to occur in mixed aggregates with "Ostorhinchus apogonoides" during summer and autumn, but form separate aggregates in winter and spring. Settlement. Whereas coral reef fish settlement tends to be dominated by larval recruitment, in at least part of Australia's Great  Barrier Reef, recruitment of "O. aureus" at any given coral reef patch tends to be by adult and juvenile migration across intervening sand and coral debris. Parasites. "O. aureus" is subject to infection by tiny cnidarian parasites from class Myxosporea. Fish specimens have been found with gall bladder infections of "Ceratomyxa apogoni", "Ceratomyxa cardinalis", and "Ellipsomyxa apogoni". Three species have also been found in skeletal muscle cells: "Kudoa cheilodipteri", "Kudoa whippsi", and "Kudoa iwatai." Behaviour. "O.aureus" is a nocturnal predator; where seagrass is adjacent to its reef, it tends to venture out further than some other members of its family . Diet. Studies of stomach contents show that "O.aureus" is a generalist predator, eating mainly planktonic and benthic crustaceans, but, unusually for its family, may at times also eat marine algae. Reproduction. "O.aureus" are external bearers, specifically mouth brooders. Adults tend to pair whilst juveniles tend to aggregate during the day time. Importance to humans. Aquariums. "O. aureus" is regularly kept by marine aquarists.