large marine fish of the family Lampridae (order Lampridiformes), widely distributed in the mid-waters of warm oceans. A deep-bodied fish with a small, toothless mouth, the opah grows to a length of about 2 m (7 feet) and a weight of 140 kg (300 pounds), although larger specimens have been reported. It is distinctively coloured, blue above and rosy below, with scarlet fins and jaws and round white spots on the body. Although uncommon, it is valued as food.