The Opah or Moonfish (Lampris guttatus) has a deep, laterally compressed oval body, with a long dorsal fin that rises high at its front end. The lateral line, on each side of the body, arches high toward the front. The pectoral fins are long and point straight up. The iridescent body is bluish above and pinkish below, usually with many white spots over much of the body. All fins, the eye ring, and the lips are scarlet. The jaws contain no teeth. The large pelvic fin has 14 to 17 rays. The scales are cycloid (a scale type with a smooth rear edge, making the scale smooth to touch) and tiny. Opah grow to ~140 cm (maximum reported ~180 cm) in length and ~75 kg (maximum reported ~ 225 to 270 kg).
Opah are found worldwide in subtropical and temperate seas (apparently avoiding equatorial waters), including the Mediterranean and Caribbean seas, from the surface to a depth of around 500 m. In the western Atlantic, they occur from the Grand Banks and Nova Scotia (Canada) to Florida, the Gulf of Mexico, and the West Indies. In the Pacific, they are found from Japan to the Gulf of Alaska and the Gulf of California. The Opah is one of only two species in the family Lampridae (the other being Lampris immaculatus, a rare species of the southern oceans south of 30º S that has a more elongate body, lacks pale spotting on the body, and has the ventral fin originating well behind the pectoral fin; Heemstra 2003). They consume a variety of pelagic animals, including squids, crabs, fish, jellyfish, and small crustaceans. They are sometimes caught by salmon and Albacore fishermen and on tuna longlines. The flesh is mostly salmon-colored, but darker over the pectoral fin. It is said to be dry but tasty and excellent when smoked. The superficially similar Ocean Sunfish (Mola mola) has no pelvic fins or red pigment, has a tiny gill opening, and has no evident caudal (tail) fin.
(Eschmeyer and Herald 1983; Robins and Ray 1986; Heemstra and Heemstra 2004)
For additional information on Opah, visit the NOAA-NMFS FishWatch page and the Monterey Bay Aquarium’s SeafoodWatch page.