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 sturgeon Acipenser oxyrhyncus; some ascend rivers to spawn; and some (the largest of inland fish) are found in landlocked waters. The largest species is the Russian sturgeon, or beluga (A. 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 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 common sturgeon is found in coastal waters and rivers of Europe and E North America. Other American species are the rock, or lake, sturgeon (A. fulvescens) of the Great Lakes and the Mississippi valley and the shovel-nosed sturgeon, or hackleback (Scaphirhynchus platorynchus; 3 ft/91 cm), also of the Mississippi valley.

Smoked sturgeon is considered a delicacy in many areas, and sturgeon eggs are the source of the better grades of caviar, sometimes in combination with eggs of the paddlefish, 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 led to a suspension of the international trade in wild caviar from the region during 2006-7.

Sturgeons are classified in the phylum Chordata, subphylum Vertebrata, class Osteichthyes, order Acipenseriformes, family Acipenseridae.

Any of about 20 species (family Acipenseridae) of large, primitive fishes that live mainly in southern Russia, Ukraine, and North America. Most species live in the sea and ascend rivers to spawn; a few live permanently in fresh water. Four tactile barbels near the toothless mouth detect invertebrates and small fishes on the mud bottom. Sturgeon flesh and eggs, or roe (caviar), are sold for food. The swim bladder is used in isinglass, a gelatin. The Baltic sturgeon (Acipenser sturio) and several other species are endangered. The Atlantic sturgeon (A. oxyrhynchus), however, is common along the eastern coast of North America and generally is about 10 ft (3 m) long and weighs about 500 lb (225 kg). Seealso beluga.

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