Sturgeon

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Sturgeon
Temporal range: Upper Cretaceous–Recent[1]
Atlantic sturgeon
(Acipenser oxyrinchus oxyrinchus)
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Superclass:Osteichthyes
Class:Actinopterygii
Order:Acipenseriformes
Family:Acipenseridae
Bonaparte, 1831
Subfamilies

Acipenserinae
Scaphirhynchinae
See text for genera and species.

 
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Sturgeon
Temporal range: Upper Cretaceous–Recent[1]
Atlantic sturgeon
(Acipenser oxyrinchus oxyrinchus)
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Superclass:Osteichthyes
Class:Actinopterygii
Order:Acipenseriformes
Family:Acipenseridae
Bonaparte, 1831
Subfamilies

Acipenserinae
Scaphirhynchinae
See text for genera and species.

Sturgeon is the common name used for some 26 species of fish in the family Acipenseridae, including the genera Acipenser, Huso, Scaphirhynchus and Pseudoscaphirhynchus. The term includes over 20 species commonly referred to as sturgeon and several closely related species that have distinct common names, notably sterlet, kaluga and beluga. Collectively, the family is also known as the true sturgeons. Sturgeon is sometimes used more exclusively to refer to the species in the two best-known genera, Acipenser and Huso.

One of the oldest families of bony fish in existence, sturgeon are native to subtropical, temperate and sub-Arctic rivers, lakes and coastlines of Eurasia and North America. They are distinctive for their elongated bodies, lack of scales, and occasional great size: sturgeons ranging from 7–12 feet (2-3½ m) in length are common, and some species grow up to 18 feet (5.5 m). Most sturgeons are anadromous bottom-feeders, spawning upstream and feeding in river deltas and estuaries. While some are entirely freshwater, very few venture into the open ocean beyond near coastal areas.

Several species of sturgeons are harvested for their roe, which is made into caviar — a luxury food which makes some sturgeons pound for pound the most valuable of all harvested fish. Because they are slow-growing and mature very late in life, they are particularly vulnerable to exploitation and to other threats, including pollution and habitat fragmentation. Most species of sturgeons are currently considered to be at risk of extinction, making them more critically endangered than any other group of species.[2]

Contents

Evolution

Acipenseriform fishes appeared in the fossil record approximately 200 million years ago, around the very end of the Triassic, making them among the most ancient of actinopterygian fishes. True sturgeons appear in the fossil record during the Upper Cretaceous. In that time, sturgeons have undergone remarkably little morphological change, indicating their evolution has been exceptionally slow and earning them informal status as living fossils.[3][4] This is explained in part by the long generation interval, tolerance for wide ranges of temperature and salinity, lack of predators due to size, and the abundance of prey items in the benthic environment.

Despite the existence of a fossil record, full classification and phylogeny of the sturgeon species has been difficult to determine, in part due to the high individual and ontogenic variation, including geographical clines in certain features, such as rostrum shape, number of scutes and body length. A further confounding factor is the peculiar ability of sturgeons to produce reproductively viable hybrids, even between species assigned to different genera. The wide range of the acipenserids and their endangered status have made collection of systematic materials difficult. These factors have led researchers in the past to identify over 40 additional species that were rejected by later workers.[5] It is still unclear whether the species in the Acipenser and Huso genera are monophyletic (descended from one ancestor) or paraphyletic (descended from many ancestors)—though it is clear that the morphologically motivated division between these two genera is not supported by the genetic evidence. There is an ongoing effort to resolve the taxonomic confusion using a continuing synthesis of systematic data and molecular techniques.[4][6]

Physical characteristics

Along with other members of the subclass Chondrostei, sturgeon are primarily cartilaginous, lack vertebral centra, and are partially covered with bony plates called scutes rather than scales. They also have four barbels—tactile organs that precede their toothless mouth and are dragged along often murky river bottoms. Sturgeon are distinctly and immediately recognizable for their elongated bodies, flattened rostra, distinctive scutes and barbels, and elongated upper tail lobes.

They are primarily benthic feeders. With their projecting, wedge-shaped snouts, they stir up the soft bottom, and use the barbels to detect shells, crustaceans and small fish, on which they feed. Having no teeth, they are unable to seize prey, though larger specimens can swallow very large prey items, including whole salmon.[7]

Sturgeon have been referred to as both the Leviathans and Methuselahs of freshwater fish. They are among the largest fish: some beluga (Huso huso) in the Caspian Sea reportedly attain over 5.5 m (18 ft) and 2000 kg[8] (4400 lbs.) while for kaluga (H. dauricus) in the Amur River, similar lengths and over 1000 kg (2200 lb) weights have been reported.[9] They are also probably the longest-lived of the fishes, some living well over 100 years and attaining sexual maturity at 20 years or more.[10] The combination of slow growth and reproductive rates and the extremely high value placed on mature, egg-bearing females make sturgeon particularly vulnerable to overfishing.

Sturgeons are polyploid; some species have four, eight, or 16 sets of chromosomes.[11]

Range and habitat

Sturgeon range from subtropical to subarctic waters in North America and Eurasia. In North America, they range along the Atlantic coast from the Gulf of Mexico to Newfoundland, including the Great Lakes and the St. Lawrence, Missouri and Mississippi Rivers, as well as along the West Coast in major rivers from California to British Columbia. They occur along the European Atlantic coast, including the Mediterranean basin, in the rivers that flow into the Black, Azov and Caspian Seas (Danube, Dnepr, Volga and Don), the north-flowing rivers of Russia that feed the Arctic Ocean (Ob, Yenisei, Lena, Kolyma), in the rivers of Central Asia (Amu Darya and Syr Darya) and Lake Baikal. In the Pacific Ocean, they are found in the Amur River along the Russian-Chinese border, on Sakhalin island, and in the Yangtze and other rivers in northeast China.[10][12]

Throughout this extensive range, almost all species are highly threatened or vulnerable to extinction due to a combination of habitat destruction, overfishing and pollution.[12]

No species are known to naturally occur south of the equator, though attempts at sturgeon aquaculture are being made in Uruguay, South Africa and other places.[13]

Most species are at least partially anadromous, spawning in fresh water and feeding in nutrient-rich, brackish waters of estuaries or undergoing significant migrations along coastlines. However, some species have evolved purely freshwater existences, such as the lake sturgeon (Acipenser fulvescens) and the Baikal sturgeon (A. baerii baicalensis), or have been forced into them by anthropogenic or natural impoundment of their native rivers, as in the case of some subpopulations of white sturgeon (A. transmontanus) in the Columbia River[14] and Siberian sturgeon (A. baerii) in the Ob basin.[15]

Conservation status

Because of their long reproductive cycles, long migrations, and sensitivity to environmental conditions, many species are under severe threat from overfishing,[16] poaching, water pollution and damming of rivers.[17] According to the IUCN, over 85% of sturgeon species are classified as at risk of extinction, making them more critically endangered than any other group of species.[2][18]

Uses

Woman selling sturgeon at a market in Türkmenbaşy, Turkmenistan
The underside and mouth of a sturgeon

Globally, sturgeon fisheries are of great value, primarily as a source for caviar, but also for flesh.

Before 1800, swim bladders of sturgeon (primarily Beluga sturgeon from Russia) were used as a source of isinglass, a form of collagen used historically for the clarification of beer, as a predecessor for gelatin, and to preserve parchments.[19]

The Jewish law of kashrut, which only permits the consumption of fish with scales, forbids sturgeon, as they have ganoid scales instead of the permitted ctenoid and cycloid scales. While all Orthodox groups forbid the consumption of sturgeon, some conservative groups do allow it.[20][21] The theological debate over its kosher status can be traced back to such 19th-century reformers as Aron Chorin, though its consumption was already common in European Jewish communities.[22] It remains a high-end staple of many Jewish delis and specialty shops.

In England, the sturgeon, along with whales and porpoises, is a royal fish, and every sturgeon caught in England is the property of the Crown.

Species

In currently accepted taxonomy, the family Acipenseridae is subdivided into two subfamilies, Acipenserinae, including the genera Acipenser and Huso, and Scaphirhynchinae, including the genera Scaphirhynchus and Pseudosaphirhynchus.[12]

A shortnose sturgeon (Acipenser brevirostrum)

See also

References

  1. ^ Froese, Rainer, and Daniel Pauly, eds. (2009). "Acipenseridae" in FishBase. January 2009 version.
  2. ^ a b "Sturgeon more critically endangered than any other group of species". IUCN, the International Union for Conservation of Nature. 18 March 2010. http://www.iucn.org/?4928. Retrieved December 6, 2010.
  3. ^ B. G. Gardiner (1984) Sturgeons as living fossils. Pp. 148–152 in N. Eldredge and S.M. Stanley, eds. Living fossils. Springer-Verlag, New York.
  4. ^ a b J. Krieger and P.A. Fuerst. (2002) Evidence for a Slowed Rate of Molecular Evolution in the Order Acipenseriformes Molecular Biology and Evolution 19:891-897.
  5. ^ W. E. Bemis, E. K. Findeis, and L. Grande. (1997). An overview of Acipenseriformes. Environmental Biology of Fishes 48:25–71.
  6. ^ F. Fontana, J. Tagliavini, L. Congiu (2001) Sturgeon genetics and cytogenetics: recent advancements and perspectives. Genetica 111: 359–373
  7. ^ Sergei F. Zolotukhin and Nina F. Kaplanova. (2007) Injuries of Salmon in the Amur River and its Estuary as an Index of the Adult Fish Mortality in the Period of Sea Migrations. NPAFC Technical Report No. 4. [1]
  8. ^ Frimodt, C., (1995). Multilingual illustrated guide to the world's commercial coldwater fish. Fishing News Books, Osney Mead, Oxford, England. 215 p.
  9. ^ Krykhtin, M.L. and V.G. Svirskii (1997). Endemic sturgeons of the Amur River: kaluga, Huso dauricus, and Amur sturgeon, Acipenser schrenckii. Environ. Biol. Fish. 48(1/4):231-239.
  10. ^ a b Berg, L.S. (1962). Freshwater fishes of the U.S.S.R. and adjacent countries. volume 1, 4th edition. Israel Program for Scientific Translations Ltd, Jerusalem. (Russian version published 1948).
  11. ^ Anderson, Rachel (2004). "Shortnose Sturgeon". McGill University. Archived from the original on 2007-10-24. http://web.archive.org/web/20071024153413/http://biology.mcgill.ca/undergra/c465a/biodiver/2000/shortnose-sturgeon/shortnose-sturgeon.htm. Retrieved 2007-08-23.
  12. ^ a b c Froese, Rainer, and Daniel Pauly, eds. (2007). "Acipenseriformes" in FishBase. 12 2007 version.
  13. ^ LA. Burtzev (1999) The History of Global Sturgeon Aquaculture. Journal of Applied Ichthyology 15 (4-5), 325–325. doi:10.1111/j.1439-0426.1999.tb00336.x
  14. ^ S. Duke, P. Anders, G. Ennis, R. Hallock, J. Hammond, S. Ireland, J. Laufle, R. Lauzier, L. Lockhard, B. Marotz, V.L. Paragamian, R. Westerhof (1999) Recovery plan for Kootenai River white sturgeon (Acipenser transmontanus), Journal of Applied Ichthyology 15 (4-5), 157–163.
  15. ^ G.I. Ruban, 1999. The Siberian Sturgeon Acipenser baerii Brandt: Structure and Ecology of the Species, Moscow, GEOS. 235 pp (in Russian).
  16. ^ Clover, Charles. 2004. The End of the Line: How overfishing is changing the world and what we eat. Ebury Press, London. ISBN 0-09-189780-7
  17. ^ Pallid Sturgeon - Montana Fish, Wildlife and Parks
  18. ^ Species, status and population trend of Sturgeon on the IUCN Red List of Threatened Species (pdf)
  19. ^ Davidson, Alan (1999). ""Isinglass"". Oxford Companion to Food. pp. 407. ISBN 0-19-211579-0.
  20. ^ http://cor.ca/en/15#12
  21. ^ http://www.bluethread.com/kashrut/sturgeon.html
  22. ^ Lupovich, Howard (2010). "7". Jews and Judaism in World History. pp. 258. ISBN 0-203-86197-3.

 This article incorporates text from a publication now in the public domainChisholm, Hugh, ed. (1911). "Sturgeon". Encyclopædia Britannica (11th ed.). Cambridge University Press.

External links