oarfish, large, elongated fish, genus Regalecus, found in the oceans worldwide except for the polar regions. Oarfish species are solitary and rarely seen by humans. The giant oarfish, R. glesne, is the world's longest bony fish, up to 17.5 ft (5.4 m) in length. It has no visible teeth and no scales, a red dorsal fin that runs the length of the body, with some 400 dorsal fin rays, and a long pelvic fin, usually with a single ray. It feeds on plankton. Because of their great length, unusual appearance, and rarity, giant oarfish are probably responsible for many sea serpent legends that have arisen in folklore. Oarfish are classified in the phylum Chordata, subphylum Vertebrata, class Actinopterygii, order Lampriformes, family Regalecidae.

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