Oarfishes are large, greatly elongated, pelagic lampriform fishes and belong 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, at up to 17 metres (56 ft) in length.
The common name oarfish is presumably in reference to either their highly compressed and elongated bodies, or to the former (but 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.
Although the larger species are considered game fish and are (to a minor extent) fished commercially, oarfish are rarely caught alive; their flesh is not well regarded due to its gelatinous consistency.
In 2001 an oarfish was filmed alive and in situ: the 1.5 metre (4.9 feet) 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 via an amiiform mode of swimming; that is, rhythmically undulating the dorsal fin whilst 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 m (16.4 feet) and 10 m (32.8 ft) in length.
Oarfish feed primarily on zooplankton, selectively straining tiny euphausiids, shrimp and other crustaceans from the water. Small fish, jellyfish and squid are also taken. Large open-ocean carnivores are all likely predators of oarfish.
The oceanodromous Regalecus glesne is recorded as spawning off Mexico from July to December; all species are presumed to be non-guarders and release brightly coloured, buoyant eggs, up to 6 millimetres (0.24 in) across, which are incorporated into the zooplankton. The eggs hatch after about three weeks into highly active larvae, that feed on other zooplankton. The larvae have little resemblance to the adults, with long dorsal and pelvic fins and extensible mouths. Larvae and juveniles have been observed drifting just below the surface. In contrast, adult oarfish are rarely seen at the surface when not sick or injured.