Sun Fish, the common name of the fishes of the diodon family and genus ortliago-riscus (Schn.). The skeleton is soft and only partially ossified; the body short and round, compressed laterally; the skin rough, covered with mucus, but without spines; jaws undivided in the middle, forming a cutting edge; mouth small, the teeth adapted for braising sea weeds and soft-bodied animals; the body is truncated posteriorly, looking as if it had been cut off at the dorsal and anal fins and then furnished with a short broad caudal; there are no ventrals, no air bladder, and no abdominal sac capable of distention; the dorsal and anal fins are more or less united to the caudal; the stomach is small, and immediately receives the biliary canal. The common sun fish (0. mola, Schn.) is almost circular, and the dorsal and anal project posteriorly, with the caudal between; on each side, near the centre, is a small pectoral, and in front of it the gill opening; the gills are arranged in comb-like fringes; it is also called moon fish and head fish.

It grows 4 or 5 ft. in length and 3 or 4 ft. in depth, with a weight of several hundred pounds; the flesh is tough and remarkably elastic, owing to the great amount of yellow elastic fibre, intricately interlaced, almost to the exclusion of white fibre and true muscle; the liver is very fat, and its oil is used for lubricating purposes on board ship, and for sprains and bruises among fishermen. It is grayish above and whitish below, with a silvery lustre when alive, and phosphorescent at night. According to Mr. Putnam, in his paper read before the American association for the advancement of science in 1870, the young differ little from the adults in shape, and do not resemble molacanthus, as Lutken and Steenstrup have said. It is sluggish in its motions, and is often seen asleep at the surface of the water. In some seasons it is common in summer in Massachusetts and New York bays, and feeds partly if not principally on medusas. There is probably no fish more infested by parasites, internally and externally. - The name sun fish is also commonly given to many me-dusse (see Jelly Fish), and in this country to the bream (see Bream).

Common Sun Fish (Orthagoriscus mola).