Tuesday, 8 February 2011

King of herrings: World's longest bony fish

King of herrings (regalecus glesne) laid on a beach
King of herrings
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Lampriformes
Family: Regalecidae
Genus: Regalecus
Species: Regalecus glesne
Conservation Status: Not assessed
Common Name(s): King of herrings, giant oarfish

The king of herrings is an extremely long fish of the Regalecidae family that holds the world's record for longest extant bony fish.

This creepy creature lives in much of the world's oceans, inhabiting depths between 200 and 1,000 meters (~650 to 3,280 ft). It is harmless to humans, despite its huge and frightening appearance.

Sightings are very rare and catching an alive specimen is even rarer! Consider yourself extremely lucky, if you ever happen to see one in person.

The species was first described by Norwegian biologist Peter Ascanius (1723–1803) in 1772. The genus name, Regalecus, signifies "belonging to a king" whereas the specific epithet (glesne) comes from "Glesnaes", the name of a farm at Glesvær, Norway, where the type specimen was discovered.

Despite of its common name, the "king of herrings" is not related to herrings. The common name is derived from its crown-like appendages and due to sightings near shoals of herrings, which fishermen believed to be guided by this strange animal.

Three men hold a small king of herrings, unknown location
This is a relatively small catch

Distribution and Habitat
The giant oarfish has a worldwide pelagic distribution and can be found in the Atlantic and Pacific oceans and the Mediterranean Sea. Individuals have been sighted from England to New England to Brazil and from Japan to New South Wales, Australia with recordings being more common in oceans with tropical to temperate waters. The species is believed to be oceanodromous (migratory), following its primary food source.

The giant oarfish appears to prefer the mesopelagic zone, a part of the pelagic zone that ranges from a depth of 200 to 1000 metres (~650 to 3,280 ft), as shown in the graph below:

The distribution of the giant oarfish in regards to depths
The layers of the pelagic zone

As aforementioned, the giant oarfish is the world's longest bony fish, reaching a maximum verified length of 11 m (~35 ft), while there have been reports of individuals of up to 17 m (55 ft). The heaviest recorded specimen was 272 kilos (~599 lb).

The giant oarfish has a ribbon-shaped body, narrowed laterally, with a dorsal fin starting from the small eyes to the tip of its tail. The skin has no scales but is covered with tubercles. The body is bright silver with streaks, spots or splotches of black or dark gray, and a bluish or brownish tinge on the head.

Individuals may have more than 400 fin rays. At the head, the rays are elongated forming a distinctive red, crown-like crest. Its pectoral and pelvic fins are nearly adjacent. The pectoral fins are stubby whereas the pelvic fins are long, single-rayed, and reminiscing of an oar in shape, widening at the tip. The head is small and has a protrusible jaw, similar to the one most lampriformes have. The mouth contains 40 to 58 gill rakers and no teeth.

Regalecus glesne has no anal fin and no gas bladder.

U.S. servicemen holding a 7 meters long giant oarfish
U.S. navy sailors holding a  7 m long giant oarfish
The original photo can be seen on page 20 of the April 1997 issue of All Hands, a U.S. Navy-owned publication
(Click to enlarge)

Swimming patterns
Individuals have been observed swimming using the dorsal fin, and also swimming in a vertical position. In February 2010, researchers announced that they had filmed an individual swimming in the Gulf of Mexico, in the mesopelagic layer. This is perhaps the only footage depicting an individual swimming in its natural setting. Most other videos and photos come from dead or dying fish, near the sea surface or ashore.

The footage was taken during a survey, using an ROV in the vicinity of Thunder Horse PDQ, and shows the fish swimming in a columnar orientation, with the tail held downward. Click here if you want to see the video in question. And here's a video from an individual shot in the Sea of Cortez, Mexico.

The king of herrings feeds on small crustaceans, squids, cnidarians (jellyfish) and zooplankton.

Old video showing a dying Regalecus glesne

Behabior & Reproduction
We have little knowledge about the species behavioral and reproductive patterns. Adults are believed to live a solitary life.

The species spawns from July to December. The eggs are 2 to 6 mm in diameter (~0.007 to 0.027 in), and float near the surface until they hatch. Larvae has been observed near the surface. Being a lampridiform, we can assume that it probably takes about 3 weeks for the eggs to hatch. Lampridiform embryos quickly develop into swimming larvae with long, distinctive rays on the pelvic and dorsal fins.

Is it dangerous?
The species has no teeth and is harmless to human. Furthermore, seeing one in close proximity is highly unlikely.

Conservation Status & Threats
Formerly considered to be a rare animal, there are rising data that the species is more abundant than previously thought. This, combined with its widespread distribution indicates that the species survival is not under immediate danger. However, its conservation status has yet to be officially assessed and thus we can't be sure for the latter.

The species is not commercially fished, but is an occasional by-catch in commercial nets. Other factors that may impact their populations include climate change, increasing carbon dioxide levels causing increased ocean acidity, ballast water allowing invasion of pathogens and  exotic species, and finally the expansion of oxygen minimum layers

Interesting Facts about the King of herrings
- Due to it's massive length and frightening appearance, it is assumed that this weird animal is the culprit behind many sea serpents sightings and stories.
- The organs of the fish are located near the head, possibly enabling it to survive the loss of large portions of its tail.
- The pelvic fins are long and slender and contain only one fin ray, with an oarlike membrane at the tip. These rays are possibly used for taste.
- Regalecus glesne should not be confused with Agrostichthys parkeri, commonly known as the Streamer fish, a very similar looking oarfish of the same family (Regalecidae), found in the southern oceans. This species grows to a maximum known length of 3 meters (~120 in). One "easy" way to tell one from the other is the number of gill rakers in their mouth. The king of herrings has 40-58 whereas the Streamer fish has only 8-10. Furthermore, the giant oarfish has no dorsal spines.

References & Further Reading
- Benfield MC, Cook S, Sharuga S, & Valentine MM (2013). Five in situ observations of live oarfish Regalecus glesne (Regalecidae) by remotely operated vehicles in the oceanic waters of the northern Gulf of Mexico. Journal of fish biology, 83 (1), 28-38 PMID: 23808690
- Dragičević, B., Pallaoro, A., Grgičević, R., Lipej, L., & Dulčić, J. (2011). On the Occurrence of Early Life Stage of the King of Herrings, Regalecus Glesne (Actinopterygii: Lampriformes: Regalecidae), in the Adriatic Sea Acta Ichthyologica Et Piscatoria, 41 (3), 251-253 DOI: 10.3750/AIP2011.41.3.13
- refas
- Taylor, J., & Saloman, C. (1968). The Oarfish, Regalecus glesne: A New Occurrence and Previous Records from the Gulf of Mexico Copeia, 1968 (2) DOI: 10.2307/1441770
- Goode, G. B. and Bean, T.H. (1895). King of herrings, a species of oarfish. From plate XVII of Oceanic Ichthyology: A Treatise on the Deep-Sea and Pelagic Fishes of the World. A Smithsonian Institution Special Bulletin. Washington: Government Printing Office.
-  Nelson, Joseph S. (2006). Fishes of the World (4th ed.). Hoboken, NJ: Wiley. p. 230. ISBN 9780471250319.
- Roberts, T. R. (2002). Payanak as a mythical animal and as the living species Regalecus glesne (Oarfish, Regalecidae, Lampridiformes). Nat. Hist. Bull. Siam Soc. 50(2), 211-224.
- Schmitter-Soto, J. J. (2008). The oarfish, Regalecus glesne (Teleostei: Regalecidae), in the western Caribbean. Caribbean Journal of Science. 44:1, 125-128.
- International Union for Conservation of Nature and Natural Resources. The IUCN Red List of Threatened Species. (2010). www.iucn.org.

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