The giant oarfish (Regalecus glesne) is the longest known bony fish on the planet. A record-breaking 7.6 metre specimen was caught in Maine, USA, tipping the scales at 272kg (that’s longer than a saltwater crocodile and heavier than a Shetland pony) but some believe they can grow even longer.
Despite their staggering size, these deep-sea fish are rarely seen because they live in the ocean’s mesopelagic zone.
Some legends warn that when they wash up on shore, an earthquake or other natural disaster may be on the way. This has led to them being ominously referred to as “harbingers of doom”.
What are oarfish?
Oarfish are long, ribbon-like fish that look like a huge type of mackerel, hence one of their nicknames: the King of Mackerel. Their common name – the oarfish – comes from the oar-like shape of their pelvic fins. People used to think these fish used their pelvic fins to row themselves through the water but they move along by undulating their dorsal fin – which runs down their entire length – while their body remains relatively still.
What do oarfish look like?
Giant oarfish have a long, flat body that's silver-coloured with no scales. They have a bright red crest on their head and a distinctive crimson dorsal fin, which is why they are sometimes known as rooster fish. This fin might be more orange or less bright in other species. Live oarfish also have dark, blotchy markings across their bodies but these fade quickly after death.
Their pelvic fin is shaped like an oar - hence the fish's name.
How big are oarfish
Oarfish are up to around 7m long and weigh around 300kg
Where do oarfish live?
These deep-sea fish are found in all the world’s oceans, apart from the polar regions. They live in the ocean’s mesopelagic zone, also known as the twilight zone because little to no light from the surface can reach such depths.
Hundreds of metres below the surface, humans wouldn’t be able to see in this dark, cold underwater world. Like many other deep-sea species, oarfish have adapted to these dim conditions. They have large eyes, to help them see in the dark, and create a bioluminescent glow, which could be a way of attracting their prey.
What do oarfish eat?
Despite their gigantic size, oarfish are filter-feeders. They eat tiny marine organisms such as krill, plankton and small crustaceans, which they strain from the water through their gill rakers. Oarfish are preyed on by larger fish and sharks. Some oarfish have been found with strange, round wounds which are probably the work of cookie-cutter sharks - one of the world's weirdest sharks -, which remove perfectly circular plugs of flesh from their victims.
How do oarfish swim?
The oarfish’s bizarre appearance is exaggerated by their strange swimming style. They move their dorsal fin in a rippling motion, like a ribbon, to swim. Unlike most other fish, oarfish can hover vertically in the water, using their dorsal fin to keep them steady. Their scale-less body reflects light, making them blend into the water around them so it is harder for predators to spot them from far away.
Do oarfish migrate?
During the night time, oarfish make a vertical migration up to the water’s surface to feed on plankton before returning to the twilight zone by daytime. Oarfish are also poor swimmers, which is why they can strand when they get caught in a strong current at the surface.
Why are these fish so rare?
Oarfish were first described in 1772 but living hundreds of metres deep, and only swimming to the surface at night, means these enormous fish are rarely seen by humans. The specimens that are found on shore or in the shallows are usually weak, sick or dying. When they get caught in a strong current, they are unable to resist and end up dying and washing up on shore.
How do they reproduce?
Oarfish usually spawn between July and December. They release their eggs and sperm into the open water and, once these fertilise each other, the eggs float near the surface of the water for around three weeks until they’re ready to hatch. The larvae look like tiny adult oarfish.
Are oarfish aggressive and are they dangerous to humans?
The monstrous, snake-like appearance of these huge fish may have inspired legends of sea serpents. However, oarfish are plankton-eaters and pose no threat to humans. They don’t even have visible teeth. Yet, there are rumours that a rare oarfish sighting is a sign of an imminent earthquake.
Why are oarfish called doomsday?
The myth of oarfish being “harbingers of doom” that predict earthquakes originates from ancient Japanese legend. Their name “ryugu no tsukai,” which translates to "the messenger from the sea dragon god's palace," refers to the belief that oarfish would travel up from the deep sea as a warning to humans when an earthquake was coming.
This belief has been solidified, for some, by instances of oarfish sightings before a significant shock. In 2011, 20 oarfish stranded in the months before a powerful tremor, and subsequent tsunami, killed over 19,000 people. In California, snorkellers saw an oarfish in California and a quake struck just two days later. Despite these curious events, there is no robust scientific evidence of a link between oarfish sightings and earthquakes.
Are oarfish endangered?
Although oarfish are rarely seen by humans, they are not considered to be endangered. The IUCN Red List of Threatened Species lists oarfish as a species of least concern. However, their population is not well studied.
How long do oarfish live?
Oarfish live up to 30 years