Oarfish

• It is so seldom seen alive that most of what is known about it comes from stranded or dying fish.
• It feeds by straining krill, small fish, squid and other crustaceans through its gill rakers.
• It lives in the mesopelagic zone of every ocean except the polar regions, between 200 and 1,000 metres deep.
• anatomíaIt can exceed 8 metres long, and its occasional appearance at the surface has inspired historical sea-serpent legends.
• It is the longest bony fish in the world. The verified record is 7.6 m and 272 kg, a specimen caught around 1885 off Maine; lengths of up to 8 m are accepted and there are reports of 11.
• Historical measurements of 15 or 17 metres are now considered very probably inaccurate.
• It swims vertically, body upright, undulating the extremely long red dorsal fin that runs the whole length of its back. That fin has between 414 and 449 rays.
• It has no scales: its silvery sheen comes from a layer of guanine, and it lacks both anal and caudal fins.
• It self-amputates its tail. Every captured specimen of its relative Regalecus russelii above a metre and a half had the tail amputated; the wound heals over but the tail does not regenerate.
• In Japan it is called Ryugu no tsukai, the messenger from the sea god's palace, and its strandings are associated with earthquakes. A study that cross-checked stranding records against earthquakes found no correlation: the perception is explained by the fact that strandings make the news, and so do earthquakes.
• It has no teeth: it filters krill and crustaceans with its gill rakers. A specimen from California had some 10,000 euphausiids in its stomach.

Skeleton type

Vertebrate - bony skeleton (fish), scaleless

Habitat & environment

Mesopelagic zone of every ocean except the polar regions, between 200 and 1,000 metres deep

Birth weight

Pelagic egg 2-4 mm; the larva a miniature of the adult

Size at birth

A larva like a miniature adult on hatching

Gestation / incubation

~3 weeks of egg development, floating near the surface

Litter / clutch size

Pelagic eggs laid by broadcast spawning, with no precise figures for fecundity

Sources consulted: Dimensions.com; MarineBio; Animal Spot; Grokipedia (Giant oarfish); Animalia.bio; Wikipedia (Giant oarfish); PMC (mitochondrial genome study)