Sturgeons and Paddlefishes: Acipenseriformes
STURGEONS AND PADDLEFISHES: AcipenseriformesBELUGA STURGEON (Huso huso): SPECIES ACCOUNT
Sturgeons (STUHR-jens) and paddlefishes are some of the largest freshwater fishes, ranging from 2.5 feet (0.8 meters) to about 28 feet (8.5 meters) in length. They have no scales and no lateral (LAT-uhr-uhl) line, or series of pores and tiny tubes along each side of the body used for sensing vibrations (vie-BRAY-shuns). Sturgeons and paddlefishes are dark on top but light or white on the bottom. Sturgeons are gray, brown, dark blue, olive green, or nearly black. Paddlefishes are bluish gray, brown, or black on top. The skeletons of sturgeons and paddlefishes are mostly cartilage (KAR-teh-lej), or tough, bendable support tissue. The only bones are the skull, the jaws, and the bones that support the pectoral (PECK-ter-uhl) fins, the front pair. These fishes have long snouts with barbels (BAR-buhls), or long, thin feelers used for the senses of taste, touch, and smell.
Sturgeons and paddlefishes live in the Northern Hemisphere in North America, Europe, and Asia.
Sturgeons and paddlefishes live in seas, rivers, and lakes. Some spend a large portion of their lives at sea but enter coastal rivers to spawn. Others live only in freshwater rivers and lakes. Sturgeons live on sand, gravel, or rock bottoms.
Sturgeons find food by swimming close to the bottom and dragging their barbels along it. They eat slow-moving insects; worms; crustaceans (krus-TAY-shuns), or animals with a soft, segmented body covered by a hard shell; and mollusks (MAH-lusks), or animals with a soft, unsegmented body usually covered by a shell. They also sometimes feed on other fishes. Paddlefishes feed by swimming through the water with their mouths open and filtering water through comblike structures called gill rakers. The gills are the organs used to get oxygen from water. Paddlefishes eat mainly crustaceans and insect larvae (LAR-vee), or insects in an early developmental stage, in plankton, or microscopic plants and animals drifting in water. They occasionally eat larger invertebrates (in-VER-teh-brehts), or animals without backbones, and other fishes.
BEHAVIOR AND REPRODUCTION
Sturgeons are active mainly during the day.
All sturgeons spawn, or produce and release eggs, in freshwater, so those that live in the sea travel to freshwater during the spring and summer months. Before spawning, sturgeons roll near the bottom and leap out of the water. Female sturgeons produce several million eggs, which are deposited over shallow, rocky areas for fertilization (FUR-teh-lih-zay-shun), the joining of egg and sperm, or male reproductive cells, to start development. Paddlefishes swim constantly, both day and night, and travel upstream in the spring to spawn. Male and female paddlefishes broadcast eggs and sperm over the gravel bottom while swimming in groups. Sturgeons and paddlefishes do not tend their young.
STURGEONS, PADDLEFISHES, AND PEOPLE
Sturgeons are valued for caviar (KA-vee-ahr), which is salted, unfertilized eggs eaten as a delicacy. The smoked meat of sturgeons also is highly valued.
Sturgeons have been valued for their caviar, the unfertilized eggs of the female, since the times of the ancient Persian, Greek, and Roman empires. The Chinese began trading caviar during the tenth century. Caviar became popular as a luxury food in Europe during the seventeenth and eighteenth centuries. In the early nineteenth century the United States was the largest producer of caviar. Caviar from beluga sturgeons is considered the best, and these sturgeons have become an endangered species because of the great demand for them.
The World Conservation Union (IUCN) lists six species of sturgeons as Critically Endangered, or facing extremely high risk of extinction in the wild; eleven species as Endangered, or facing very high risk of extinction in the wild; and eight species as Vulnerable, or facing high risk of extinction in the wild. The U.S. Fish and Wildlife Service lists the Alabama, pallid, short-nose, and white sturgeons as Endangered, meaning that they are in danger of extinction throughout all or most of their range, and the gulf sturgeon as Threatened, or likely to become endangered in the near future.
Physical characteristics: The beluga is the largest sturgeon. It can be as long as 28 feet (8.5 meters) and can weigh 2,866 pounds (1,300 kilograms), although such large ones are rare. The body is gray or dark green with lighter sides and a white belly.
Geographic range: Beluga sturgeons live in the Black, Caspian, and Adriatic Seas in Europe and Asia and in most of their tributaries.
Habitat: Beluga sturgeons live near the shores of seas and in large channels of rivers.
Diet: Young beluga sturgeons eat invertebrates, such as mollusks, worms, and crustaceans. Adults eat other fishes.
Behavior and reproduction: Adult beluga sturgeons live at sea for most of the year but travel up large rivers to spawn in late spring. The young travel back to the sea immediately after hatching. Beluga sturgeons mature slowly and live as long as 150 years. Females may produce more than seven million eggs, but reproduction occurs only once every five to seven years. Beluga sturgeons spawn by scattering eggs and sperm in the water over the rocky bottom.
Beluga sturgeons and people: Beluga sturgeons are valued as a source of caviar.
Conservation status: The IUCN lists beluga sturgeons as Endangered. They may be extinct in the Adriatic Sea. ∎
FOR MORE INFORMATION
Berra, Tim M. Freshwater Fish Distribution. San Diego, CA: Academic Press, 2001.
Ricciuti, Edward R. Fish. Woodbridge, CT: Blackbirch, 1993.
Schultz, Ken. Ken Schultz's Field Guide to Freshwater Fish. New York: Wiley, 2004.
Schultz, Ken. Ken Schultz's Field Guide to Saltwater Fish. New York: Wiley, 2004.