The Oarfish: Nature’s Deep-Sea Oddity

The Oarfish is one of the oddest fish in the ocean. It is the longest of all the bony fishes (only some of the largest sharks get bigger), and it may have sparked the legend of the Sea Serpent.

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Oarfish on display at Los Angeles County Museum of Natural History

The Oarfish, Regalecus glesne, is a bizarre-looking animal. Measuring up to fifty feet long, it is only a few inches thick, giving it the alternate name of Ribbonfish. In the Mediterranean region, it is sometimes called the King of Herrings.

The long slender body has a bright silvery-blue sheen with some darker splotches, but the most striking feature is the bright red dorsal fin, supported by spines, that runs like a crest along the back for its entire length, and the two long red pectoral fins. Despite its impressive size, the Oarfish has a small head with a tiny toothless mouth. They are filter feeders, which trap krill, small fish and squid in cartilaginous “rakes” located inside their mouths, extending from the gill arches. One adult that washed ashore in California was found to have over 10,000 krill in its stomach.

The Oarfish begins life as a scattered mass of eggs, about an eighth of an inch in diameter, that float on the sea surface. Spawning seems to take place in the late summer. When the larvae hatch, they stay near the surface and feed on microscopic plankton, but as they grow they migrate to deeper depths, with the adults being found from 600 feet to 1500 feet.

As deep-water fish, they are only rarely encountered, and nearly everything known about the Oarfish comes from specimens that have been accidentally caught by deep-sea commercial fishermen. (They have a flabby and jelly-like flesh and are not eaten by humans–they are probably hunted by sharks.) The Oarfish has no swim bladder, and when it is sick or injured, it often floats up to the sea surface, where it is sometimes encountered by passing ships (which may have given rise to the legend of the Sea Serpent). On several occasions, dead Oarfish have been found washed up on shore in various places in the Atlantic and Pacific (one Oarfish found on a beach in Bermuda in 1860 was reported as a Sea Serpent). The species was first scientifically described in 1772 from a dead specimen that washed ashore in the Mediterranean. Examples of Oarfish have been found in every warm area of ocean, so it is believed that they are distributed worldwide.

It wasn’t until 2001 that the first living Oarfish was filmed in the ocean, by a team of Navy divers working on repairing an ocean buoy in the Bahamas; this young Oarfish was about 5 feet long. In 2008, oceanographers in the Gulf of Mexico filmed an Oarfish at depth, measuring between 15 and 30 feet long. During the subsequent Project Serpent to study the species, scientists using remotely-piloted submersibles were able to film living Oarfish at depth on five occasions. And in 2014 a kayaker on a trip in California sponsored by the Shedd Aquarium was able to film an Oarfish near the surface.

These observations of living Oarfish added some details about their behavior. It was found that the fish do not swim by undulating their body like a snake, or by paddling along with their pectoral fins, as previously thought. Instead, the body is held straight, but is propelled forward by rippling waves along the dorsal fin. It was also seen that the Oarfish often feeds on plankton and small squid by floating along vertically in the water. And since the Oarfish has always been observed alone, it is believed that they lead solitary lives.

At least one of the Oarfish’s relatives, the Streamerfish, is known to be able to produce a weak electric current in its body, like an electric eel. And one scientific team from New Zealand, which got the opportunity to handle a trapped Oarfish that lived for a short time, reported that it too was capable of generating mild electric shocks.

In October 2013, an 18-foot Oarfish was found washed up on a beach on Catalina Island, off the California coast. It was given to the Los Angeles County Museum of Natural History, where it is now on display.

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Forgotten mysteries, oddities and unknown stories from history, nature and science.