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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).
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.
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).
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).
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).
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).
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).
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.
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).
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).
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).
Unknown. Probably stable.
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).
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?
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