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sturgeon,primitive fish of the northern regions of Europe, Asia, and North America. Unlike evolutionarily advanced fishes, it has a fine-grained hide, with very reduced scalation, a mostly cartilaginous skeleton, upturned tail fins, and a mouth set well back on the underside of the head. It also has widely separated rows of heavy guard scales, four barbels or feelers that hang below the head and help to locate food, and a gas bladder from which isinglass is made. Sturgeons feed by sucking in their food—e.g., crayfish, snails, larvae, and small fishes—from the water bottom through their small, toothless, fleshy-lipped mouths.
Some species are marine, e.g., the Atlantic and Gulf sturgeons Acipenser oxyrhyncus; some ascend rivers to spawn; and some (the largest of inland fish) are found in landlocked waters. The largest species is the beluga (A. huso or Huso huso), of the Caspian and Black seas; it reaches a length of 13 ft (396 cm) and a weight of up to a ton (900 kg). The white, or Pacific, sturgeon (A. transmontanus) may weigh over half a ton (450 kg) and attain a length of 12 ft (366 cm). The green sturgeon is a smaller Pacific variety, and the European sea, or common, sturgeon is found in coastal waters and rivers of Europe and E North America. Other American species are the lake, or rock, sturgeon (A. fulvescens) of the Great Lakes and the Mississippi valley, the shovelnose sturgeon, or hackleback (Scaphirhynchus platorynchus; 3 ft/91 cm), of the Mississippi valley, and the pallid sturgeon (S. albus), of the Missouri and Mississippi valleys, an endangered species.
Smoked sturgeon is considered a delicacy in many areas, and sturgeon eggs are the source of the better grades of caviarcaviar
, the roe (eggs) of various species of sturgeon prepared as a piquant table delicacy. The ovaries of the fish are beaten to loosen the eggs, which are then freed from fat and membrane by being passed through a sieve.
..... Click the link for more information. , sometimes in combination with eggs of the paddlefishpaddlefish,
large freshwater fish, Polyodon spathula, of the Mississippi valley, also called spoonbill or duckbill and named for its flattened, paddle-shaped snout. The largest specimens weigh well over 150 lb (67.5 kg) and reach 6 ft (183 cm) in length.
..... Click the link for more information. , a close relative. Russia, Iran, and other countries surrounding the Caspian Sea have undertaken conservation measures, including aquaculture and setting catch quotas, to save the threatened Russian sturgeon from extinction, but declines in Eurasian species of sturgeon have led to several suspensions of the international trade in wild caviar from the region since 2001. Sturgeon are also raised on fish farms in a number nations outside the Caspian basin.
Sturgeons are classified in the phylum ChordataChordata
, phylum of animals having a notochord, or dorsal stiffening rod, as the chief internal skeletal support at some stage of their development. Most chordates are vertebrates (animals with backbones), but the phylum also includes some small marine invertebrate animals.
..... Click the link for more information. , subphylum Vertebrata, class Actinopterygii, order Acipenseriformes, family Acipenseridae.