Fish
Oarfish
Regalecus glesne · also called giant oarfish, king of herrings, ribbonfish
An oarfish is a silver ribbon up to eight metres long that lives in the dark middle depths of the open ocean and is almost never seen alive. It swims standing on its tail, rippling a red fin that runs the length of its body, and it is the most likely real animal behind centuries of sea-serpent stories.
Overview
The giant oarfish, Regalecus glesne, is the longest bony fish in the world — reliably to about 8 metres, with unverified claims well beyond — though the body is a thin, tapering ribbon only a few centimetres thick. It lives in the open ocean worldwide, at depths of roughly 200 to 1,000 m, and eats krill and other small crustaceans, plus small fish and squid, strained from the water by a small toothless mouth.
Built strangely
Oarfish have no scales — the silver sheen is a rub-off coating of guanine crystals — and swim head-up in a vertical column, moving by undulating the long red dorsal fin. They can amputate their own tail at set break points and live on, since all the vital organs are packed into the front of the body, and healthy individuals are often found missing their rear half.
Myth and mystery
In Japan the oarfish is the ryugu no tsukai, and its appearance is said to foretell an earthquake — but a formal study of strandings versus seismic records found no real link; deep-sea fish surface when sick or storm-tossed. Living oarfish were not filmed in the wild until the 2000s, and their lifespan, breeding, and numbers remain poorly known.
Status
Least Concern by default — a huge global range, not fished, rarely taken as bycatch — but with very little direct data, since the species is almost never seen alive.
Oarfish: common questions
Is the oarfish really a sea serpent?
The oarfish is almost certainly behind a large share of historical sea-serpent reports. It is enormous, up to 8 metres or more, extremely thin, silver, and snake-like, with a crest of red fin rays on the head and a fin running the length of the back that ripples as it swims, so a sick oarfish at the surface, seen from a ship in poor light, matches the classic description of a long, undulating sea monster with a crest or mane. There is no giant unknown serpent; there is a real, rarely seen, very long fish that looks the part. Living oarfish are harmless plankton and small-fish eaters with no teeth.
How long can an oarfish get?
The giant oarfish, Regalecus glesne, is the longest bony fish known. Well-documented specimens reach about 8 metres, and there are older, unverified reports of individuals of 11 metres and even 15 metres, which are hard to confirm because a dead oarfish is fragile and often incomplete and because length is easy to overestimate for such a thin, ribbon-shaped animal. Even at 8 metres the body is only a few centimetres thick and weighs a fraction of what a shark or tuna of similar length would. Sharks such as the whale shark grow longer overall but are cartilaginous, not bony fish.
Do oarfish predict earthquakes?
There is a widespread belief, strongest in Japan, that oarfish rise from the deep before a large earthquake, tied to the folklore of the oarfish as a messenger of the sea god. The idea gained attention after several oarfish stranded in Japan in the year before the 2011 Tohoku earthquake. However, a 2019 study that compared about 300 deep-sea fish appearances in Japan, mostly oarfish and slender ribbonfish, against earthquake records found no statistically meaningful relationship. Oarfish come to the surface when they are sick, dying, or caught in strong currents and storms, and given how often small earthquakes occur in Japan, a coincidence is easy to find. There is no known biological mechanism linking the fish to seismic activity.
What happens to the oarfish that wash up on beaches?
They are usually already dead or dying. An oarfish is a deep-water animal with a delicate, scaleless, silver-coated body that is not built to withstand surface conditions, wave action, or handling, so one that has come shallow because of illness or injury deteriorates fast and rarely survives even if pushed back. Scientists value strandings highly because they are almost the only source of specimens, and stranded oarfish are often collected by museums and aquariums for study of their anatomy, stomach contents, and parasites. Attempts to keep oarfish alive in aquariums have generally failed within hours or days.