Oarfish are large, greatly elongated, pelagiclampriform fish and belong to the small familyRegalecidae. 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 nameoarfish 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 Latinregalis, 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.
The dorsal fin originates from above the (relatively small) eyes and runs the entire length of the fish. Of the approximately 400 dorsal fin rays, the first 10 to 12 are elongated to varying degrees, forming a trailing crest embellished with reddish spots and flaps of skin at the ray tips. The pelvic fins are similarly elongated and adorned, reduced to 1 to 5 rays each. The pectoral fins are greatly reduced and situated low on the body. The anal fin is completely absent and the caudal fin may be reduced or absent as well, with the body tapering to a fine point. All fins lack true spines. At least one account, from researchers in New Zealand, describes the oarfish as giving off "electric shocks" when touched.
Like other members of its order, the oarfish has a small yet highly protrusible oblique mouth with no visible teeth. The body is scaleless and the skin is covered with easily abraded, silvery guanine. In the streamer fish (Agrostichthys parkeri), the skin is clad with hard tubercles. All species lack gas bladders and the number of gill rakers is variable.
Oarfish coloration is also variable; the flanks are commonly covered with irregular bluish to blackish streaks, black dots, and squiggles. These markings quickly fade following death. The giant oarfish is by far the largest member of the family at a published total length of 11 metres (36 ft) (with unconfirmed reports of 15 metres (49 ft) or more) and 272 kilograms in weight. The streamer fish is known to reach 3 metres (9.8 ft) in length whilst the largest recorded specimen of Regalecus russelii measured just 540 centimetres standard length.
The members of the family are known to have a worldwide range. However, specific encounters with live individuals in situ are rare and distribution information is collated from records of oarfishes caught or washed ashore.
Rare encounters with divers and accidental catches have supplied what little is known of oarfish behaviour and ecology. Apparently solitary animals, oarfish may frequent significant depths up to 1,000 metres (3,300 ft). An oarfish measuring 3.3 metres (11 ft 4 in) and 63.5 kg (140 lb) was reported to have been caught on 17 February 2003 by Ms Val Fletcher using a fishing rodbaited with squid, at Skinningrove, United Kingdom.
A photograph on display in bars, restaurants, guesthouses and markets around Laos and Thailand that is captioned, "Queen of Nāgas seized by American Army at Mekhong River, Laos Military Base on June 27, 1973 with the length of 7.80 metres," is a hoax. The photograph was taken by Dr. Leo Smith of The Field Museum, of an oarfish found in September 1996 by United States Navy SEAL trainees on the coast of Coronado, California, USA.
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 ft) and 10 m (32.8 ft) in length.
As part of the SERPENT Project, five observations of apparently healthy oarfish Regalecus glesne by remotely operated vehicles were reported from the northern Gulf of Mexico between 2008 and 2011 at depths from within the epipelagic and mesopelagic zones. These observations include the deepest verified record of R. glesne (463–492 m (1,519–1,614 ft)) and the first record of an arthropodectoparasite (isopod).
From December 2009 to March 2010, unusual numbers of the slender oarfish Regalecus russelii (竜宮の使い “Ryūgū-No-Tsukai”,) known in Japanesefolklore as the Messenger from the Sea God's Palace, appeared in the waters and on the beaches of Japan; the appearance of which is said to portend earthquakes.
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 oceanodromousRegalecus 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 inches) 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.