Regalecus glesne (Ascanius, 1772)

Submitted by danieljwallach 26 Jan
Scientific name:  Regalecus glesne (Ascanius, 1772)
Common names
Common names:  King of Herrings
Common names:  Giant Oarfish
Behaviour
Behaviour: 

R. glesne usually lives in depths of 200-1000m, eating a variety of fishes and invertebrates (Paxton and Eschmeyer, 1998), especially krill and euphausiids (Roberts, 2002), squid, and cnidarians (Schmitter-Soto, 2008).  They are only found rarely, sometimes washed up on shore after being injured by shark predation (Schmitter-Soto, 2008) or lancetfish predation (Haedrich, 1964).

R.glesne have been observed suspended with the head up in the water column, and have the ability to descend rapidly via undulations of their long dorsal fin (Edwards, 2010).

Conservation
Conservation: 

Regalecus glesne are rarely observed.  When observed, they are usually injured, as their standard habitat is sufficiently deep as to not interact with humans often.  As such, there is little way of knowing how threatened they are beyond via extrapolation from limited numbers of sightings.  However, they make no appearance on conservation lists such as the IUCN list (IUCN, 2010), and so are not considered endangered.

Diagnostic description
Diagnostic Description: 

Regalecidae is differentiated from the related Trachipteridae most easily by the long pelvic fins consisting of only one fin ray.

One way to differentiate Regalecus glesne from  Agrostichthys parkeri, the only other species in the family Regalecidae, is the number of gill rakers: while R. glesne has 40-58, A. parkeri has 8-10.   R. glesne has no dorsal spines, A. parkeri has many. Also, while R. glesne is subtropical, distributed in Bermuda and both coasts of Florida, from Southern California to Chile, and in the Caribbean, A. parkeri is found in Southern Hemisphere temperate waters (Robins and Ray, 1986; Schmitter-Soto, 2008).

Distribution
Distribution: 

Regalecus glesne is globally found in tropical to warm temperate waters from England to New England to Brazil and from Japan to New South Wales, Australia (Schmitter-Soto, 2008).

General description
General description: 

Regalecus glesne, known by the fanciful name of "king of herrings" or the more stoic "oarfish", is the longest of the Teleost fish, reaching an average length of 5-8m and a record of 17m. (Paxton and Eschmeyer, 1998)  It has a long, ribbonlike body with a red dorsal fin running its entire length  (Robins and Ray, 1986).  The dorsal fin is longest in front, making a cockscomb on the head (Eschmeyer and Herald, 1983).  It has 260-412 fin rays (Nelson, 2006).  The pelvic fins are long and slender, only containing one fin ray, with an oarlike membrane at the tip (Robins and Ray, 1986).  These rays are possibly used for taste (Paxton and Eschmeyer, 1998). The body tapers to a tiny caudal fin which is entirely lost in some specimens (Eschmeyer and Herald, 1983). It has 143-170 vertebrae (Nelson, 2006).  There is no anal fin, and no scales (Nelson, 2006).  The skin is covered with tubercles (Robins and Ray, 1986).  R. glesne has small eyes, no teeth, and no swim bladder (Nelson, 2006).  The body is gray to silvery with varied black markings and red fins (Robins and Ray, 1986; Eschmeyer and Herald, 1983). 

Habitat
Habitat: 

R. glesne is a marine fish which lives in the mesopelagic zone, between 200 and 1000 m in depth (Nelson, 2006).  It has also rarely been found at the surface, possibly leading to many sea serpent myths (Roberts, 2002).

Morphology
Morphology: 

The long (~8 m) and slender silvery body has red fins, most notably a red dorsal fin running the length of the body with a corkscomb on the head, and a long slender pelvic fin with one fin ray, with an oarlike membrane on the tip.  The skin is covered in tubercles (Robins and Ray, 1986; Eschmeyer and Herald, 1983). 

Movement and dispersal
Migration: 

Migration patterns unknown.  However, given smaller average specimen size in American waters than in European, possible migration as adults from west to east is possible, at least in the North Atlantic populations (Schmitter-Soto, 2008).  The migration would probably be oceanodromous, limited to the oceanic environment, given R. glesne have never been found in freshwater.

Physical description
Size: 

R. glesne is the longest bony fish, with average length of 5-8m and record length of 17m.  Possibly weigh up to 227 kg (Eschmeyer and Herald, 1983).

Reproduction and life history
Reproduction: 

Little is known specifically about the reproduction of R. glesne, but as a lampridiform fish, it probably lays large pelagic eggs of about 2-6 mm in diameter via broadcast spawning, which incubate at the surface for up to three weeks in some species (Paxton and Eschmeyer, 1998).  Larvae have been found at the surface that have been identified as R. glesne (Bauchot, 1995).

Lampridiform embryos quickly develop into swimming larvae with long, distinctive rays on the pelvic and dorsal fins (Paxton and Eschmeyer, 1998).

Given seasonal changes in records, it is thought that R. glesne spawn between July and December (Bauchot, 1995).  

Trends and threats
Threats: 

There is very little data from which to derive evidence of threats to Regalecus populations.  There are probably none derived from immediate human influence, as there is very little interaction between R. glesne and humans.

However, Robison suggests that deep sea diversity is threatened in general by a wide array of factors, including climate change, increasing carbon dioxide levels leading to increased ocean acidity, ballast water allowing invasion of pathogens and exotic species, and the expansion of oxygen minimum layers (Robison 2009).

Trends: 

Unknown.  Probably stable.

Trophic strategy
Trophic strategy: 

Regalecus glesne is a filter-feeder which uses its gill rakers to feed on the plankton of the mesopelagic oceans, straining the water's contents into its three-foot stomach (Paxton and Eschmeyer, 1998).  It catches small fish, cnidarians, krill, euphausiids, and other small invertebrates.  It has been found in shark and lancetfish stomachs, and so cannot be considered a true top predator (Haedrick, 1964; Schmitter-Soto, 2008).

Uses
Uses: 

Regalecus glesne is a remarkable fish.  It is probably responsible for many sea serpent stories.  Beyond simply explaining sailors' tales, learning about the biomechanical properties of the movement of the longest bony fish in the world could help lead to optimizations of biomimetic engineering for large and long transport vehicles.

Finally, study and promotion of such an amazing fish could lead to interest in the biological sciences.  Who wouldn't want to study such living legends?

References
References: 
Bauchot, M. L. (1995). Regalecidae. Reyes de arenque. In Guia FAO para Identification de Especies para lo fines de la Pesca (ed. W. Fischer, F. Krupp, W. Schneider, C. Sommer, K. E. Carpenter, and V. Niem), p. 1418. Pacifico Centro-Oriental. Rome: FAO.
Edwards, L. (2010). Bizarre giant oarfish filmed. http://www.physorg.com/news185001953.html.
Eschmeyer, W. N. and Herald, E.S. (1983). A Field Guide to Pacific Coast Fishes of North America. Boston: Houghton Mifflin.
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.
Haedrich, R. L. (1964). Food habits and young stages of North Atlantic Alepisaurus (Pisces, Iniomi). Breviora MCZ. 201.
International Union for Conservation of Nature and Natural Resources. The IUCN Red List of Threatened Species. (2010). www.iucn.org.
Nelson, J. S. (2006). Fishes of the World. 4th ed. Hoboken: Wiley.
Paxton, J. R. and Eschmeyer, W. N., eds. (1998). Encyclopedia of Fishes. 2nd ed. Singapore: Kyodo.
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.
Robins, C. R. and Ray, G.C. (1986). Field Guide to Atlantic Coast Fishes. Boston: Houghton Mifflin.
Robison, B.H. (2009). Conservation of deep pelagic diversity. Conservation Biology. 23:4.
Schmitter-Soto, J. J. (2008). The oarfish, Regalecus glesne (Teleostei: Regalecidae), in the western Caribbean. Caribbean Journal of Science. 44:1, 125-128.
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Attribution
Rights holder:  Daniel Wallach

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