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Sturgeon Temporal range: Upper Cretaceous-Holocene[1]
Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Acipenseriformes
Family:	Acipenseridae Bonaparte, 1831
Subfamilies
Acipenserinae Scaphirhynchinae See text for genera and species.

Play media

Beluga sturgeon in an aquarium.

Sturgeon is the common name for the 27 species of fish belonging to the family Acipenseridae. Their evolution dates back to the Triassic some 245 to 208 million years ago.^[2] The family is grouped into four genera: Acipenser, Huso, Scaphirhynchus and Pseudoscaphirhynchus. Four species may now be extinct.^[3] Two closely related species, Polyodon spathula (American paddlefish) and Psephurus gladius (Chinese paddlefish, possibly extinct) are of the same order, Acipenseriformes, but are in the family Polyodontidae and are not considered to be "true" sturgeons. Both sturgeons and paddlefish have been referred to as "primitive fishes" because their morphological characteristics have remained relatively unchanged since the earliest fossil record.^[4][5] Sturgeons are native to subtropical, temperate and sub-Arctic rivers, lakes and coastlines of Eurasia and North America.^[6]

Sturgeons are long-lived, late-maturing fishes with distinctive characteristics, such as a heterocercal caudal fin similar to that of sharks, and an elongated spindle-like body that is smooth-skinned, scaleless and armored with 5 lateral rows of bony plates called scutes. Several species can grow quite large, typically ranging 7–12 feet (2-3½ m) in length. The largest sturgeon on record was a Beluga female captured in the Volga estuary in 1827, weighing 1,571 kg (3,463 lb) and 7.2 m (24 ft) long. Most sturgeons are anadromous bottom-feeders which migrate upstream to spawn but spend most of their lives feeding in river deltas and estuaries. Some species inhabit freshwater environments exclusively while others primarily inhabit marine environments near coastal areas, and are known to venture into open ocean.

Several species of sturgeon are harvested for their roe which is processed into caviar—a luxury food and the reason why caviar-producing sturgeons are among the most valuable of all wildlife resources.^[7] They are particularly vulnerable to overexploitation and other threats, including pollution and habitat fragmentation. Most species of sturgeon are considered to be at risk of extinction, making them more critically endangered than any other group of species.^[8]

In art, a sturgeon is the symbol on the coat of arms for Saint Amalberga of Temse.^[9]

Evolution

Acipenseriform fishes appeared in the fossil record some 245 to 208 million years ago presumably near the 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.^[10][11] 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 bony plated armor, or scutes, and the abundance of prey items in the benthic environment. Although their evolution has been remarkably slow, they are a highly evolved living fossil, and do not closely resemble their ancestral chondrosteans. They do however still share several primitive characteristics, such as heterocercal tail, reduced squamation, more fin rays than supporting bony elements, and unique jaw suspension.^[12]

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. While ray-finned fishes (Actinopterygii) have a long evolutionary history culminating in our most familiar fishes, past adaptive evolutionary radiations have left only a few survivors, like sturgeons and garfish.^[13]

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 scientists.^[14] 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.^[11][15]

Physical characteristics

Sturgeon skull - a, Rostrum; b, nasal capsule; c eye-socket; d, foramina for spinal nerves; e, notochord; g, quadrate bone; h, hyomandibular bone; i, mandible; j. basibranchials; k, ribs; l, hyoid bone; I, II, III, IV, V, branchial arches.

Sturgeons retain several primitive characters among the bony fishes. Along with other members of the subclass Chondrostei, they are unique among bony fishes because the skeleton is almost entirely cartilaginous. Notably, however, the cartilagineous skeleton is not a primitive character, but a derived one: sturgeon ancestors had bony skeletons.^[12][16][17] They also lack vertebral centra, and are partially covered with 5 lateral rows of bony plates called scutes rather than scales.^[18] They also have four barbels—sensory organs that precede their wide, toothless mouths. They navigate their riverine habitats traveling just off the bottom with their barbels dragging along gravel, or murky substrate. Sturgeon are recognizable for their elongated bodies, flattened rostra, distinctive scutes and barbels, and elongated upper tail lobes. The skeletal support for the paired fins of ray-finned fish is inside the body wall, although the ray-like structures in the webbing of the fins can be seen externally.

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^[19] (4400 lb) while for kaluga (H. dauricus) in the Amur River, similar lengths and over 1,000 kg (2,200 lb) weights have been reported.^[20] They are also among the longest-lived of the fishes, some living well over 100 years and attaining sexual maturity at 20 years or more.^[21] 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.^[22]

Life cycle

Sturgeons are long-lived, late maturing fishes. Their average lifespan is 50 to 60 years, and their first spawn does not occur until they are around 15 to 20 years old. Sturgeons are broadcast spawners, and do not spawn every year because they require specific conditions. Those requirements may or may not be met every year due to varying environmental conditions, such as the proper photoperiod in Spring, clear water with shallow rock or gravel substrate where the eggs can adhere, and proper water temperature and flow for oxygenation of the eggs. A single female may release 100,000 to 3 million eggs but not all will be fertilized. The fertilized eggs become sticky and will adhere to the bottom substrate upon contact. It takes 8–15 days for the embryos to mature into larval fish. During that time, they are dependent on their yolk sac for nourishment.^[23][24] River currents carry the larvae downstream into backwater areas, such as oxbows and sloughs where the free-swimming fry will spend their first year feeding on insect larvae and crustacea. During their first year of growth, they will reach 18 to 20 cm (7.1 to 7.9 in) in length and migrate back into the swift-flowing currents in the main stem river.

Range and habitat

The 8th Century Saint Amalberga of Temse was said to have crossed the river Scheldt, riding on a giant sturgeon

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 and Idaho to British Columbia. They occur along the European Atlantic coast, including the Mediterranean basin, especially in the Adriatic Sea and the rivers of North Italy;^[25] 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 some rivers in northeast China.^[21][26]

Throughout this extensive range, almost all species are highly threatened or vulnerable to extinction due to a combination of habitat destruction, overfishing, and pollution.^[26]

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.^[27]

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^[28] and Siberian sturgeon (A. baerii) in the Ob basin.^[29]

Behavior

The underside and mouth of a sturgeon

Sturgeon are primarily benthic feeders, with a diet of shells, crustaceans and small fish. Exceptionally, both Huso species, the white sturgeon, and the pallid sturgeon feed primarily on other fish as adults. They feed by extending their syphon-like mouths to suck food from the benthos. Having no teeth, they are unable to seize prey, though larger individuals and more predatory species can swallow very large prey items, including whole salmon.^[30] Sturgeons feed non-visually. They are believed to use a combination of sensors, including olfactory, tactile and chemosensory cues detected by the four barbels, and electroreception using their ampullae of Lorenzini.^[31]

The sturgeons' electroreceptors are located on the head and are sensitive to weak electric fields generated by other animals or geoelectric sources.^[32] The electroreceptors are thought to be used in various behaviors such as feeding, mating and migration.^[31]

Many sturgeon leap completely out of the water,^[34] usually making a loud splash which can be heard half a mile away on the surface and probably further under water. It is not known why they do this, but suggested functions include group communication to maintain group cohesion, catching airborne prey, courtship display, or to help shed eggs during spawning. Other plausible explanations include escape from predators, shedding parasites, or to gulp or expel air.^[35] Another explanation is that it "simply feels good".^[33] Leaping sturgeon are known to occasionally cause injuries to humans in boats;^[36] in 2015, a 5-year-old girl died after a sturgeon leapt from the Suwannee River and struck her.^[37]

Conservation status

Because of their long reproductive cycles, long migrations, and sensitivity to environmental conditions, many species are under severe threat from overfishing,^[38]poaching, water pollution, and damming of rivers.^[39] There is also a noticeable decline in sturgeon populations as the demand for caviar increases. 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.^[8][40]

A 2013 study on the critically endangered sturgeon populations in the Danube River Basin determined that ongoing illegal fishing activity and caviar trade is threatening the future of Danube sturgeons.^[41] Jutta Jahrl, a conservation expert with the World Wildlife Federation stated that "Romania and Bulgaria are home to the only viable wild sturgeon populations left in the European Union, but unless this sophisticated illegal fishing is stopped, these fish are doomed”.^[41]

Uses

Woman selling sturgeon at a market in Türkmenbaşy, Turkmenistan

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 wine and beer, as a predecessor for gelatin, and to preserve parchments.^[42]

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.^[43][44] 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.^[45]

Along with whales, sturgeons are royal fish.^[46] Under the law of the United Kingdom any sturgeons captured within the realm are personal property of the monarch.^[47]

Classification

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.^[26]

	Subfamily	Genera	Image	Species	Common name	Max reported			Fish- base	FAO	IUCN status
						Length	Weight	Age
A c i p e n s e r i d a e	Acipenserinae	Acipenser		Acipenser baerii	Siberian sturgeon	200 cm	210 kg	60 yrs	[48]	[49]	Endangered[50]
				Acipenser brevirostrum	Shortnose sturgeon	143 cm	23 kg	67 yrs	[51]	[52]	Endangered[53]
				Acipenser dabryanus	Yangtze sturgeon	250 cm			[54]	[55]	Critically endangered[56]
				Acipenser fulvescens	Lake sturgeon	274 cm	125 kg	152 yrs	[57]	[58]	Least Concern[59]
				Acipenser gueldenstaedtii	Russian sturgeon	236 cm	115 kg	46 yrs	[60]	[61]	Critically endangered[62]
				Acipenser medirostris	Green sturgeon	250 cm	159 kg	60 yrs	[63]	[64]	Near threatened[65]
				Acipenser mikadoi	Sakhalin sturgeon	150 cm			[66]	[67]	Critically endangered[68]
				Acipenser naccarii	Adriatic sturgeon	200 cm	25 kg		[69]	[70]	Critically endangered[71]
				Acipenser nudiventris	Fringebarbel sturgeon	200 cm	80 kg		[72]	[73]	Critically endangered[74]
				Acipenser oxyrinchus	Atlantic or Gulf sturgeon	403 cm		60 yrs	[75]	[76]	Near threatened[77]
				Acipenser persicus	Persian sturgeon	242 cm	70 kg		[78]		Critically endangered[79]
				Acipenser ruthenus	Sterlet	125 cm	16 kg	20 yrs	[80]	[81]	Vulnerable[82]
				Acipenser schrenckii	Amur sturgeon	300 cm	190 kg	65 yrs	[83]	[84]	Critically endangered[85]
				Acipenser sinensis	Chinese sturgeon	400 cm	600 kg	13 yrs	[86]	[87]	Critically endangered[88]
				Acipenser stellatus	Starry sturgeon	220 cm	80 kg	27 yrs	[89]	[90]	Critically endangered[91]
				Acipenser sturio	European sea sturgeon	600 cm	400 kg	100 yrs	[92]	[93]	Critically endangered[94]
				Acipenser transmontanus	White sturgeon	610 cm	816 kg	104 yrs	[95]	[96]	Least concern[97]
		Huso		Huso dauricus	Kaluga sturgeon	560 cm	1000 kg	80 yrs	[98]	[99]	Critically endangered[100]
				Huso huso	Beluga sturgeon	800 cm	1571 kg	118 yrs	[101]	[102]	Critically endangered[103]
	Scaphi- rhynchinae	Scaphi- rhynchus		Scaphirhynchus albus	Pallid sturgeon	200 cm	130 kg	41 yrs	[104]	[105]	Endangered[106]
				Scaphirhynchus platorynchus	Shovelnose sturgeon	100 cm	7 kg	43 yrs	[107]	[108]	Vulnerable[109]
				Scaphirhynchus suttkusi	Alabama sturgeon				[110]		Critically endangered[111]
		Pseudo- scaphi- rhynchus		Pseudoscaphirhynchus fedtschenkoi	Syr Darya sturgeon	65 cm			[112]		Critically endangered[113]
				Pseudoscaphirhynchus hermanni	Dwarf sturgeon	28 cm	0.5 kg	6 yrs	[114]	[115]	Critically endangered[116]
				Pseudoscaphirhynchus kaufmanni	Amu Darya sturgeon	75 cm	2 kg		[117]	[118]	Critically endangered[119]

Species

A young lake sturgeon (Acipenser fulvescens)

European sturgeon (Huso huso) feeding on another fish

Play media

Pallid sturgeon (Scaphirhynchus albus) showing siphoning feeding behaviour

• 
  Family Acipenseridae Bonaparte, 1831
  
  
  
  • Subfamily Acipenserinae
    
    
    
    • Genus Acipenser Linnaeus, 1758
      
      
      
      • 
        Acipenser baerii J. F. Brandt, 1869
        
        
        
        • 
          Acipenser baerii baerii J. F. Brandt, 1869 (Siberian sturgeon)
        
        
        • 
          Acipenser baerii baicalensis Nikolskii, 1896 (Baikal sturgeon)
        
        
        
        
      
      
      • 
        Acipenser brevirostrum Lesueur, 1818 (Shortnose sturgeon)
      
      
      • 
        Acipenser dabryanus A. H. A. Duméril, 1869 (Yangtze sturgeon)
      
      
      • 
        Acipenser fulvescens Rafinesque (Lake sturgeon)
      
      
      • 
        Acipenser gueldenstaedtii J. F. Brandt & Ratzeburg, 1833 (Russian sturgeon)
      
      
      • 
        Acipenser medirostris Ayres, 1854 (Green sturgeon)
      
      
      • 
        Acipenser mikadoi Hilgendorf, 1892 (Sakhalin sturgeon)
      
      
      • 
        Acipenser naccarii Bonaparte, 1836 (Adriatic sturgeon)
      
      
      • 
        Acipenser nudiventris Aleksey Leontievitch Lovetsky, 1828 (Fringebarbel sturgeon)
      
      
      • 
        Acipenser oxyrinchus Mitchill, 1815
        
        
        
        • 
          Acipenser oxyrinchus desotoi Vadim Dimitrievitch Vladykov, 1955 (Gulf sturgeon)
        
        
        • 
          Acipenser oxyrinchus oxyrinchus Mitchill, 1815 (Atlantic sturgeon)
        
        
        
        
      
      
      • 
        Acipenser persicus Nikolai Andreyevich Borodin, 1897 (Persian sturgeon)
      
      
      • 
        Acipenser ruthenus Linnaeus, 1758 (Sterlet)
      
      
      • 
        Acipenser schrenckii J. F. Brandt, 1869 (Amur sturgeon)
      
      
      • 
        Acipenser sinensis J. E. Gray, 1835 (Chinese sturgeon)
      
      
      • 
        Acipenser stellatus Pallas, 1771 (Starry sturgeon)
      
      
      • 
        Acipenser sturio Linnaeus, 1758 (European sea sturgeon)
      
      
      • 
        Acipenser transmontanus J. Richardson, 1836 (White sturgeon)
      
      
      
      
    
    
    • Genus Huso J. F. Brandt & Ratzeburg, 1833
      
      
      
      • 
        Huso dauricus (Georgi, 1775) (Kaluga sturgeon)
      
      
      • 
        Huso huso (Linnaeus, 1758) (Beluga sturgeon)
      
      
      
      
    
    
    
    
  
  
  • Subfamily Scaphirhynchinae
    
    
    
    • Genus Scaphirhynchus Heckel, 1835
      
      
      
      • 
        Scaphirhynchus albus (Forbes & Robert Earl Richardson, 1905) (Pallid sturgeon)
      
      
      • 
        Scaphirhynchus platorynchus (Rafinesque, 1820) (Shovelnose sturgeon)
      
      
      • 
        Scaphirhynchus suttkusi James D. Williams (ichthyologist) & Glenn H. Clemmer, 1991 (Alabama sturgeon)
      
      
      
      
    
    
    • Genus Pseudoscaphirhynchus Nikolskii, 1900
      
      
      
      • 
        Pseudoscaphirhynchus fedtschenkoi (Kessler, 1872) (Syr Darya sturgeon)
      
      
      • 
        Pseudoscaphirhynchus hermanni (Kessler, 1877) (Dwarf sturgeon)
      
      
      • 
        Pseudoscaphirhynchus kaufmanni (Kessler, 1877) (Amu Darya sturgeon)
      
      
      
      
    
    
    
    
  
  
  
  

Notes

References

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

External links

Wikimedia Commons has media related to Acipenser.

Wikisource has the text of the 1905 New International Encyclopedia article Sturgeon.

• FishBase info on Acipenser


• 
  Official website of the World Sturgeon Conservation Society
  


• 
  Sturgeon feeding on the remains of a fish at Eccleston Delph, Lancashire England – Set of images on Flickr


• Information on North American sturgeons with photographs


• Gallery of movie clips showing different species of sturgeon