Thursday, December 29, 2011

Regalecus glesne, the Giant Oarfish

A washed up Giant Oarfish found in 1996 by members of the U.S. Navy.

Regalecus glesne, or more commonly known as the Giant Oarfish or the King Of Herrings, is quite possibly the longest living fish and certainly the longest living bony-fish.  The debate stems from the fact that the first Giant Oarfish to be encountered was a specimen that had washed up in Scotland in 1808.  The individual was recorded to have a length of 56 ft (17 m).  However, other than this single instance, the largest specimen encountered was only 36 ft (11m).  This has led some to claim that the first recording was in error while others do not find it surprising and believe that individuals of 50 ft (15.24 ft) in the wild may not be uncommon.  But until further data can be found, the limit of 36 ft is the most often cited.

This disagreement as to the limit in size for the Giant Oarfish puts it as either the longest fish period or simply the longest bony-fish.  To compare its size, the Whale Shark (Rhincodon typus), generally considered to be the largest living fish, has a maximum recorded size of 41.50 ft (12.65 m).

Despite being an enormous fish and having a range throughout the worlds tropical and temperate oceans, the fish is rarely sighted.  The few times it has been encountered have almost exclusively been when specimens have washed ashore or into shallow water, either dead or dying.  Though a few instances of live individuals being encountered in the wild have occurred.  Though no matter the state of the fish, encounters are sure to grab regional, if not worldwide attention.

A taxidermied Giant Oarfish in the Museum of Natural History of Vienna.
The Giant Oarfish's natural habitat is at a depth of between 600 feet (200 m) and 3,000 feet (1,000 m), though healthy individuals have been occasionally known to rise to the surface for short periods for unknown reasons.  It is during these rare excursions to the oceans surface, or when they have washed ashore or into shallow water, that it is thought that these unusual fish gave rise to the myth of the sea serpent.  While ill, it is not uncommon for individuals to swim with their heads and the crests of their dorsal fins to be sticking out in a way that resembles elaborate spines or horns.  In fact, it is one can still find the occasional old map with images of sea monsters that curiously resemble Oarfish.

It is not hard to see how sightings of this fish could give rise to myths of sea serpents.
The most notable feature of the Giant Oarfish is its long and laterally compressed body.  Despite having an immense length, they have a lateral length of only around and inch or two.  They also have pinkish to crimson red fins.  The most obviously being the body length dorsal fin with its large crests and its long, thin pelvic fins.  In fact, other then these and the small pectoral fins, these fish have lost all of their other fins.  They also have a highly extendable sideways mouth, much like those found in certain flatfish such as flounder.  There body is a brilliantly shiny silver with blue to brown spots and stripes, however these spots and stripes will often fade as the fish grows ill.  However the fish's shiny exterior will remain.  The reason for this shininess is not due to scales, for they utterly lack any.  Instead, they have large amounts of Guanine embedded within their skin (the same molecule that is used in DNA) that gives them their metallic luster.

Like many of the largest organisms in the worlds oceans, all Oarfish and their closely related cousins, the Ribbonfish and the Crestfish, feed on some of the smallest of organisms.  Feeding primarily on the zooplankton where they selectively strain out their preferred foods, such as tiny euphausiids (krill), shrimp and other crustaceans.  They have also been known to occasionally eat smaller squid, fish and sea jellies.  Using their highly extendable mouths, they feed in a fashion similar to many other fish, by extending their mouth and sucking in their prey.  Their food is then ingested whole.

The source of the common names for the Giant Oarfish come from the fact that people once believed the fish swam by undulating its body while using its long pelvic fins to 'row' through the water.  This, however, is simply a myth.  It moves by undulating its long dorsal fin while keeping its body perfectly straight, in what is known as amiiform locomotion.  Its other common name, the King Of Herrings, comes from yet another myth.  This one being traced back to fishermen occasionally seeing the Giant Oarfish around the same time as they were catching Herring and them assuming that the fish was leading the school.  With the rather regal look of the Giant Oarfish, it is not hard to see why this was so.  In fact, this myth gave rise to its genus name, as Regalecus means regal.

In the wild, the fish swim vertacally through the water column, with their tail end facing down and their head pointing straight up.  It is believed this may be so that the fish can spot the silhouettes of its prey against the light from the surface, much like many other species of deep water fish are known to do.

The Giant Oarfish is known to be a migratory species.  Specifically, they are what is known as oceanodromous, meaning that their migrations never take them out of sea water.  They migrate to waters off of Mexico between July and December to spawn, then back to their original locations throughout the worlds oceans.  The fish are strict loners so males and females will release their gametes into the water to be fertilized as part of the plankton.  The eggs are brightly colored and buoyant, floating to the surface where they are fertilized and hatch after about three weeks into a larval form that stays near the surface, feeding upon the zooplankton that they live amongst.  These larva are so morphologically distinct that their identity was long a mystery until more developed specimens were found and the link to adult Oarfish was made.

The larval form of the Giant Oarfish.
A slightly more mature individual.
A healthy Giant Oarfish has been caught on camera at its normal depth only once.  The video was taken by an ROV (Remotely Operated Vehicle) at a depth of 2509 ft (765 m) in the Gulf Of Mexico near a deep-sea oil rig.  I have included the video of this amazing event for your viewing pleasure.


The Giant Oarfish is truly a marvelous fish that brings a sense of wonder for scientists and the public alike whenever it is encountered.  It is a prime example of how evolution can take life in truly fantastical directions.
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