Sturgeon is the common name for 27 species of fish belonging to the Acipenseridae family. Their evolution started from the Triass about 245 to 208 million years ago. Families are grouped into four genera: Acipenser , Huso , Scaphirhynchus and Pseudoscaphirhynchus . Four species are now extinct. Two closely related species, Polyodon spathula (paddlefish) and Psephurus gladius (Chinese paddlefish fish, possibly extinct) have the same order, Acipenseriformes, but are in the family of Polyodontidae and not regarded as the "right" sturgeon. Sturgeon and paddlefish have been referred to as "primitive fish" because their morphological characteristics have remained relatively unchanged since the earliest fossil records. Sturgeon comes from subtropical, subtropical and sub-arctic rivers, lakes and coastlines of Eurasia and North America.
Sturgeon is a long-lived fish, an adult fish with distinctive characteristics, such as a heterocercal tail fins similar to a shark, and an elongated spindle body, smooth, nonfat and armored with 5 lateral rows of bone plates called scutes. Some species can grow quite large, usually ranging from 7-12 feet (2-3Ã, m) in length. The largest sturgeon fish ever recorded was a Beluga female captured at the Volga estuary in 1827, weighing 1,571 kg (3,463 pounds) and a length of 7.2 m (24 ft). Most sturgeons are anadromous bottom feeders that migrate upstream to lay eggs but spend most of their lives eating in river delta and river estuaries. Some species inhabit the freshwater environment exclusively while others primarily inhabit the marine environment near coastal areas, and are known to venture out into the open sea.
Several species of sturgeons are harvested for their eggs that are processed into caviar - sumptuous foods and the reason why the caviar sturgeon is the most valuable of all wildlife resources. They are particularly vulnerable to over-exploitation and other threats, including pollution and habitat fragmentation. Most of the sturgeon species are considered at risk of extinction, making them more endangered than other species of species.
In art, the sturgeon is a symbol on the emblem for Saint Amalberga of Temse.
Video Sturgeon
Evolution
The acipenseriform fish appears in the fossil record about 245 to 208 million years ago, perhaps near the end of the Triassic, making them among the most ancient fish of the actinopterygian fish. The true sturgeon fish appears in the fossil record during the Upper Cretaceous. At that time, the sturgeons had undergone very small morphological changes, showing their evolution very slowly and making their informal status as living fossils. This is described in part by long-term intervals, tolerances for a wide range of temperatures and salinity, a lack of predators because of the size and layers of armor, or scutes, and the abundance of prey in benthic environments. Although their evolution is very slow, they are highly evolved living fossils, and not very similar to their ancestral chondrosteans. Yet they still share some primitive characteristics, such as heterocercal tails, reduced squamation, finer rays over bone supporting elements, and unique jaw suspensions.
Despite the existence of the fossil record, the full classification and phylogeny of the sturgeon species is difficult to determine, in part due to high individual and ontogenic variations, including geographical clines in certain features, such as rostrum forms, number of flutes and body. length. The next confounding factor is the unique ability of the sturgeon to produce hybrids that can reproduce reproductively, even between species assigned to different genera. While the ray-finned fish has a long evolutionary history that culminates in the most familiar fish, the radiation adaptation of the past leaves only a few survivors, such as sturgeon and garfish.
A wide variety of acipenserids and their endangered status have made the collection of systematic material difficult. These factors have led researchers in the past to identify more than 40 additional species rejected by later scientists. It remains unclear whether the species in the Acipenser and Huso genera are monophyletic (derived from one ancestor) or paraphyletic (derived from many ancestors) - although it is clear that the morphologically motivated division between the two this genera is not supported by genetic evidence. There is an ongoing effort to resolve the taxonomic confusion using systematic data synthesis and sophisticated molecular techniques.
Maps Sturgeon
Physical Characteristics
Sturgeons retain some of the primitive characters among the bony fish. Together with other members of the Chondrostei subclass, they are unique among bony fish because the skeleton is almost entirely vertebrated. In particular, however, the cartilaginous skeleton is not a primitive character, but is derived: the sturgeon ancestor has bony bone. They also do not have vertebral centra, and some are covered with 5 lateral rows of bone plates called scales rather than scales. They also have four thorns - sense organs that precede their wide and toothless mouths. They navigate their moving river habitats from below with thorns dragged along gravel, or cloudy substrates. Sturgeon is recognizable because of its elongated body, flattened rostra, distinctive flavor and trumpet, and an elongated upper tail lobe. Skeletal support for paired fins of ray-finned fish is inside the body wall, although the structure of a ray in a fin canine is seen externally.
Sturgeon has been referred to both as Leviathans and Methuselahs of freshwater fish. They are the largest fish: some Beluga (huso huso huso) in the Caspian Sea are reported to be over 5.5 m (18 ft) and 2000 kg (4400 pounds) while for H. dauricus ) on the Amur River, the same length and over 1,000 kg (2,200 pounds) of weights have been reported. They are also among the longest-lived fish, some live over 100 years and reach sexual maturity in 20 years or more. The combination of slow growth and the level of reproduction and a very high value placed on the mature woman, egg-bearing makes the sturgeon very susceptible to overfishing.
Sturgeon is polyploid; some species have four, eight, or 16 sets of chromosomes.
Life cycle
Sturgeon is a long-lived, mature fish. Their average age is 50 to 60 years, and their first seed does not occur until they are about 15 to 20 years old. Sturgeon is a broadcaster, and does not lay eggs every year because they need certain conditions. These requirements may or may not be met annually due to various environmental conditions, such as appropriate photoperiods in Spring, clear water with stone or shallow pebbles in which the eggs can be attached, and appropriate water temperature and flow for oxygenation of the egg. A single female can release 100,000 to 3 million eggs but not all will be fertilized. The fertilized egg becomes sticky and will attach to the bottom substrate after contact. It takes 8-15 days for the embryo to mature into a larvae. During that time, they depend on their yolk sacs for food. River currents carry downstream larvae to remote areas, such as oxbow and slough where free-swimming fish will spend their first year feeding on insect and crustacean larvae. During the first year of growth, they will reach a length of 18 to 20 cm (7.1 to 7.9 inches) and migrate back to the heavy currents in the main mother river.
Range and habitat
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The sturgeon range from subtropical waters to subaritics in North America and Eurasia. In North America, they are located along the Atlantic Coast from the Gulf of Mexico to Newfoundland, including the Great Lake and the St. Lawrence, Missouri, and Mississippi, as well as along the West Coast on the major rivers from California and Idaho to British Columbia. They occur along the Atlantic coast of Europe, including the Mediterranean basin, especially in the Adriatic Sea and rivers in Northern Italy; in the river that flows into the Black Sea, Azov, and Caspian Sea (Danube, Dnepr, Volga and Don); a river that flows north of Russia feeding 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 on the Amur River along the Russian-Chinese border, on Sakhalin Island, and on the Yangtze River and other rivers in northeastern China.
Throughout this vast range, almost all species are highly threatened or vulnerable to extinction due to a combination of habitat destruction, overfishing, and pollution.
No species is known to occur naturally south of the equator, although sturgeon fish cultivation efforts are underway in Uruguay, South Africa, and elsewhere.
Most species are at least partially anadromous, laying in fresh water and feeding on nutrient-rich, brackish-mouth estuarine waters or undergoing significant migration along the coastline. However, some species have evolved purely the existence of freshwater, such as the lake sturgeon ( Acipenser fulvescens ) and sturgeon Baikal ( A. Baerii baicalensis ), or have been forced into it. by anthropogenic or natural tethering of their native rivers, as in the case of some white sturgeon subpopulations ( A. transmontanus ) in the Columbia River and Siberian sturgeon ( A. baerii ) in the Ob basin.
Behavior
Sturgeons are primarily benthic feeders, with dietary shells, crustaceans and small fish. Incredible, both Huso species, white sturgeon, and pale sturgeon feed primarily on other fish as adults. They feed by lengthening their siphon-like mouth to suck food from benthos. Because they have no teeth, they can not catch prey, although larger individuals and more predatory species can ingest large prey, including whole salmon. Sturgeon feeds non-visually. They are believed to use a combination of sensors, including olfactory, touch and chemosensory cues detected by all four barbels, and electroreception using their ampullae from Lorenzini.
Electroreceptors sturgeons' are located at the head and sensitive to weak electric fields generated by other animals or geoelectric sources. The electroreceptors are considered to be used in a variety of behaviors such as eating, mating and migration.
Many sturgeon fish jump out of the water, usually making a loud spark that can be heard half a mile away on the surface and perhaps further underwater. It is not known why they do this, but suggested functions include group communication to maintain group cohesion, capture air prey, dating appearance, or to help release eggs during spawning. Other plausible explanations include escaping predators, spilling parasites, or for swallowing or wasting air. Another explanation is that "it just feels good". Standing sturgeon fish are known to occasionally cause injury to humans in boats; in 2015, a 5-year-old girl died after a sturgeon fish jumped from the Suwannee River and attacked her.
Conservation status
Due to their long reproductive cycle, long migration, and sensitivity to environmental conditions, many species are under severe threats from overfishing, poaching, water pollution, and river damming. There was also a marked decline in the sturgeon population as demand for caviar increased. According to IUCN, more than 85% of the sturgeon species are classified as at risk of extinction, making them more critically threatened than other species.
A 2013 study of endangered sturgeon fish populations in the Danube River Basin determined that ongoing illegal fishing activities and caviar trade threatened the future of the Danube sturgeon. Jutta Jahrl, a conservation expert with the World Wildlife Federation stated that "Romania and Bulgaria are home to the only remaining living wild sturgeon fish population in the European Union, but unless sophisticated illegal fishing is halted, these fish are destined to".
Usage
Globally, sturgeon fisheries are very valuable, especially as a source of caviar, but also for meat.
Prior to 1800, bladders swimming sturgeons (especially Beluga's sturgeon from Russia) were used as a source of isinglass, a form of collagen used historically for clarification of wine and beer, as a precursor to gelatin, and to preserve parchment.
Kashrut Jewish law, which permits only fish consumption by scales, prohibits sturgeons, because they have ganoid scales, not ctenoid scales and cycloids are allowed. While all Orthodox groups forbid the consumption of the sturgeon, some conservative groups do allow it. The theological debate on the status of halal can be traced back to 19th century reformers like Aron Chorin, although his consumption is common in the European Jewish community.
Together with whales, sturgeon fish is a royal fish. Under the laws of the British Empire, every sturgeon captured within the territory is the king's private property.
Classification
Source of the article : Wikipedia
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