Oarfish are large, greatly elongated, pelagic lampriform fish belonging to the small family Regalecidae. Found in all temperate to tropical oceans yet rarely seen, the oarfish family contains four species in two genera. One of these, the giant oarfish (Regalecus glesne), is the longest bony fish alive, growing to up to 11 m (36 ft) in length. That is not enough to qualify as the longest fish, however, as some of the cartilaginous fish such as the basking shark and whale shark are even longer.
The common name oarfish is thought to be in reference either to their highly compressed and elongated bodies, or to the now discredited belief that the fish “row” themselves through the water with their pelvic fins. The family name Regalecidae is derived from the Latin regalis, meaning “royal”. The occasional beachings of oarfish after storms, and their habit of lingering at the surface when sick or dying, make oarfish a probable source of many sea serpent tales.
In 2001, an oarfish was filmed alive in situ: the 1.5-metre (4.9-foot) fish was spotted by a group of U.S. Navy personnel during the inspection of a buoy in the Bahamas. The oarfish was observed to propel itself by an amiiform mode of swimming; that is, rhythmically undulating the dorsal fin while keeping the body itself straight. Perhaps indicating a feeding posture, oarfish have been observed swimming in a vertical orientation, with their long axis perpendicular to the ocean surface. In this posture, the downstreaming light would silhouette the oarfishes’ prey, making them easier to spot.
In July 2008, scientists captured footage of the rare fish swimming in its natural habitat in the Gulf of Mexico. It is the first ever confirmed sighting of an oarfish at depth, as most specimens are discovered dying at the sea surface or washed ashore. The fish was estimated to be between 5 and 10 m (16 and 33 ft) in length.