Sturgeons and Paddlesfishes

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About Sturgeons and Paddlesfishes

STURGEON
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. The family Acipenseridae belongs to the order Acipenseriformes. The family Polyodontidae (paddlefishes) is also a member of the order Acipenseriformes.

One of the oldest families of bony fish in existence, they 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 (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 either vulnerable, endangered or critically endangered.

Evolution
Sturgeon and related paddlefish first appear in the fossil record approximately 200 million years ago, making them among the most ancient of ray-finned fishes. In that time they have undergone remarkably little morphological change, indicating that their evolution has been exceptionally slow and earning them informal status as living fossils. This is explained in part by the long inter-generation time, 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, it has been difficult to fully classify the sturgeon species or unambiguously determine their phylogeny. This is 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. It is still unclear whether the species in the Asipenser 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.

Physical characteristics
Along with other members of the Chondrostei and the Acipenseriformes order, sturgeon are primarily cartilagenous, lack a vertebral centrum, and are covered with bony plates called scutes rather than scales. They also have four barbels - unique 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 wedgeshaped snout 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 and even baby seals.

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 and 2000 kg while for kaluga (H. dauricus) in the Amur River similar lengths and over 1000 kg weights have been reported. 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. 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 4, 8, or 16 sets of chromosomes.

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 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.

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

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.

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), Sterlet (Acipenser ruthenus) 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 and Siberian sturgeon (A. baerii) in the Ob basin.

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.

Sturgeon Hybrids
* Sterlet x Beluga (Huso huso) = (Bester)
* Sterlet x Siberian (Acipenser baerii)
* Sterlet x Diamond (Acipenser gueldenstaedtii)
The most common sturgeon hybrid is Diamond x Siberian. There is also Italian x Diamond. Hybrids are hardier than their parents.

PADDLEFISH
Paddlefish (family Polyodontidae) are primitive Chondrostian ray-finned fishes. The paddlefish can be distinguished by its large mouth and its elongated snout called a rostrum (bill). These spatula-like snouts comprise half the length of their entire body. There are only two extant species of these fish: the Chinese and the American paddlefish. The American species is Missouri's State Aquatic Animal.

These fish are not closely related to sharks, but they do have some body parts that resemble those of sharks such as their skeletons, primarily composed of cartilage, and deeply forked heterocercal tail fins.

In some areas, paddlefish are referred to as "Spoonbill", "Spoonies" or "Spoonbill Catfish". Paddlefish are also extremely oily. Mounted specimens occasionally leak an oily substance

Species
The Chinese paddlefish (Psephurus gladius) lives in the Yangtze River. Nine-feet (three-meters) specimens weighing 300 kilograms (660 lb) have been recorded; reports of 7 metres (23 ft) fish exist, although the existence of such large specimens is doubtful.

The American paddlefish (Polyodon spathula) lives in the slow-flowing waters of the Mississippi River, Missouri River, Yellowstone River, Ohio River and Oklahoma River systems (and was historically found in the Great Lakes). In May 2000, the Canadian Species at Risk Act listed the Paddlefish as being extirpated in Canada. The American paddlefish is one of the largest freshwater fish in North America. They commonly reach 5 feet (1.5 m) or more in length and can weigh more than 60 pounds (27 kg). The largest American paddlefish on record was caught in Iowa and weighed 198 pounds (90 kg). However, the largest unofficial record was 206 pounds from Lake Cumberland in Kentucky. Postcards from the 1960s show a photo of this huge fish. This type of fish's age is hard to determine but many scientists think that they live 50 years or more.

Fossils of other paddlefish have been found. One such species is Crossopholis magnicaudatus. C. magnicaudatus has been found in the Green River Shale deposit of Wyoming and dates to the Eocene.

Physical characteristics
Early investigators once thought that paddlefishes used their snouts to dig vegetation from the bottom of lakes and rivers. In fact, they feed by filtering out zooplankton from the water, using filaments on their gill arches called "gill rakers".

The rostrum contains receptors in its rostrum that can detect weak electrical fields, suggesting that they use their rostrum as an antenna to detect zooplankton. Even though the rostrum seems to help the fish feed, it has been observed that fish with severely damaged or missing rostrums are able to feed and are just as healthy as other fish with them intact.

The rostrum also helps the fish to feed by acting as a stabilizer. As the fish moves through the water with its mouth open, the rostrum creates lift, much like a wing of an airplane. This helps the fish by keeping its head in a steady position and helps it keep from diving to the bottom.

Paddlefish lay their eggs in midstream over bare rocks or gravel. The eggs are adhesive, and stick to the rocky substrate. After hatching, the young are swept downstream and grow to adulthood in deep freshwater pools.

Status
Paddlefish were at one time very abundant in most central U.S. river systems, but populations have declined greatly due to over harvesting, sedimentation, and river modification. One of the major reasons for declining paddlefish numbers are the dams constructed up and down major U.S. river systems. The dams block paddlefish migration routes that are very important to the fish for spawning. One other reason for the decreased numbers is over fishing. Pennsylvania Fish and Boat Commissioners are reintroducing the species to historical habitats in the Ohio and Allegheny rivers in an effort to establish a secure breeding population once again. Reintroduction efforts for a species take many years to mature enough fish to help the population reach mature breeding numbers.

Caviar harvest
During the last century, paddlefish and sturgeon have stimulated the world stock trades with their eggs (roe), called caviar. Paddlefish and sturgeon are two of the most important fish for freshwater caviar. Paddlefish take many years before they are able to spawn. A female may take 9 to 10 years, when they are about 42 inches long, and males 7 years old and 40 inches long are able to spawn. When able to spawn, the female releases adhesive eggs randomly over the water bottom and abandons them. They are capable of producing over one-half million eggs a year, but they may not spawn every year.

Current threats
Due to the value of their eggs, paddlefish are a constant target for poachers, and they are subsequently a protected resource over a large part of their range. Additionally, in many of the 22 states that paddlefish reside, habitat destruction is causing their numbers to decrease more rapidly. Paddlefish need free flowing rivers that have shallow pools with sandy, rocky bottoms. These types of areas are perfect for their spawning. Water must also be at the right temperature for the fish to be capable of spawning. Since today's rivers are constantly being modified by the construction of dams, dredging, and excessive water removal for farming purposes, these types of areas are hard for the paddlefish to locate.

In some areas, free flowing lakes with reservoirs are able to provide paddlefish with the right breeding habitat. One such area is the Missouri River-Lake Sakakawea system in North Dakota. This area is capable of producing good paddlefish numbers because it is a free flowing system with many good areas for paddlefish to spawn. Fishing for paddlefish in violation of local fishing regulations in some states is a felony.

Fishing for paddlefish
In some states, paddlefish are abundant enough to allow for sport fishing. Taking paddlefish is done with a bow and arrow, a spear, or by snagging--because paddlefish are filter feeders, they cannot be caught with conventional lures. For snagging, typically, anglers use a large treble hook (2/0 to 4/0 in size), weighted heavily to pull the hook to the bottom. Heavy duty rods, 7' to 15' in length with a heavy duty reel and line, complete the rig, which the angler moves in a sweeping motion to hook the fish in the fins or tail.

Chinese Paddlefish
Chinese Paddlefish (Psephurus gladius), also known as Chinese Swordfish, are among the largest freshwater fish. It is one of two extant paddlefish species, the other being the American Paddlefish. It is also called "elephant fish" because its snout resembles an elephant trunk. More poetically, it is sometimes referred to as the "Giant Panda of the Rivers", not because of any physical resemblance to a panda, but because of its rarity and protected status.

The Chinese Paddlefish is the People's Republic of China's first-level protected animal. Its belly is white and back and head grey. They live mostly in the middle or lower part of the Yangtze (Chang Jiang), occasionally in large lakes. They feed on other fish, with a small amount of crabs and crayfish. They are sexually mature at seven or eight, with a body length of 2 metres and a weight of 25 kilograms.

It is said that a zoologist recorded around the 1950s that some fishermen caught a paddlefish of 7-metres, although the authenticity of the story is unconfirmed. It is claimed that the Chinese paddlefish can grow to 23 feet and weigh 1,100 pounds, but little research on a maximum size can be conducted today due to the species' scarcity.

Due to overfishing, the Chinese Paddlefish is endangered now, and officially recognized by the People's Republic in 1983 to prevent fishing of paddlefish young or adults. Paddlefish are also threatened by dams (like the Three Gorges Dam), which divide the population into isolated groups. The fish are rarely seen, recently raising concerns that the species might already be extinct. However, a 3.6-meter, 250 kilogram specimen was killed by illegal fishing on January 8, 2007, in Jiayu County on the Yangtze River.

They were once given the scientific names of Polyodon gladius and Polyodon angustifolium.

The text in this article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia articles "Sturgeon", "Paddlefish" and Chinese paddlefish".




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