Oarfish are large and extremely long pelagic lampriform fish belonging to the small family Regalecidae.

[1] Found in areas spanning from temperate ocean zones to tropical ones, yet rarely seen, the oarfish family contains three species in two genera.

[2] One of these, the giant oarfish (Regalecus glesne), is the longest bony fish alive, growing up to about 8 m (26 ft) in length.

[3] The common name oarfish is thought to allude 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.

[5] Their rarity and large size, and their habit of lingering at the surface when sick or dying, make oarfish a probable source of sea serpent tales.

[7] In the streamer fish (Agrostichthys parkeri), the skin is clad with hard tubercles;[8] in Regalecus russelii, there are tubercules along the midline of the belly.

Analysis of the mitochondrial genome of an R. glesne specimen clusters the species with Trachipterus trachypterus and Zu cristatus, two other Lampriformes.

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.

[20] An oarfish measuring 3.3 m (11 ft) and 63.5 kg (140 lb) was caught in February 2003 using a fishing rod baited with squid at Skinningrove, United Kingdom.

[21] In July 2008, scientists for the first time captured footage of an oarfish swimming in its natural habitat in the mesopelagic zone in the Gulf of Mexico.

[22] 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 within the epipelagic and mesopelagic zones.

[25] Oarfish were found to have late or slow flight responses towards approaching remotely operated vehicles, supporting the hypothesis that they have few natural predators.

[25] From December 2009 to March 2010, unusual numbers of the slender oarfish Regalecus russelii[13] appeared in the waters and on the beaches of Japan.

[26] In 2016, Animal Planet aired an episode of the television series River Monsters named "Deep Sea Demon" in which Jeremy Wade was filmed with a live oarfish.

[4] From January to February 2019, researchers tested and recorded the first successful instance of artificial insemination and hatching of Regalecus russellii using gonads from two washed-up specimens.

[35] The slender oarfish, (竜宮の使い "Ryūgū-No-Tsukai"), known in Japanese folklore as the 'Messenger from the Sea God's Palace', is said to portend earthquakes.

[37][38] After the 2011 Tōhoku earthquake and tsunami which killed over 20,000 people, many in Japan pointed to the 20 oarfish washed up on the country's beaches in 2009 and 2010 in line with this reputation as a harbinger of doom.