Latin name

Acipenser medirostris

Other names

No information

Identification

Sturgeon and paddlefish, best known for their black caviar, belong to the order Acipenseriformes, but at some distant point they split from their common ancestor. As a result, sturgeon belong to the family Acipenseridae and paddlefish belong to the family Polyodontidae. Both species are considered bony fishes, but their skeletons are mostly cartilaginous. Their closest living relatives are the gar and the bowfin. Like paddlefish, sturgeons vary in appearance. Each species has a heterocercal tail (the upper lobe is larger than the lower lobe), an intestine with a spiral valve, a spiral (breathing hole), an upper jaw not fused to the skull, and a cartilaginous backbone in adults. The sturgeon has five rows of bony scales (scaly plates), a bottom-oriented, widening, tube-like mouth with fleshy lips, four spines, an elongated snout, and a teardrop-shaped body.

Distribution

There are nine recognized species of sturgeon in North America. White sturgeon (Acipenser transmontanus) and green sturgeon (A. medirostris) are found along the west coast of North America. Atlantic sturgeon (A. oxyrinchus oxyrinchus) and shortnose sturgeon (A. brevirostrum) are found on the east coast. Lake sturgeon (A. fulvescens) inhabit the Great Lakes and the upper Mississippi River. Shovelnose sturgeon (Scaphirhynchus platorhynchus) and pallid sturgeon (S. albus) occur in the Mississippi River system. The Alabama sturgeon (S. suttkusi) is endemic to the Mobile River drainage in Alabama. Gulf sturgeon (A. oxyrinchus desotoi), a subspecies of Atlantic sturgeon, is common in all Gulf drainages from Tampa Bay, Florida, west to the Mermantau River, Louisiana.

Habitat

Sturgeon are most often found on or near the bottom. They usually concentrate in deep pools in river bends. During migration (spring and fall), juveniles and adults occupy deep pools in brackish water at the boundary between fresh and salt water in coastal rivers.

Size

Early growth is rapid and juveniles can reach adult size in as little as 3 years.

Life history and Behavior

Members of the genus Scaphirhynchus, like lake sturgeon, are potamodromous. They live in rivers or lakes and migrate upstream to smaller tributaries or rivers to spawn. Their migrations are similar to those of paddlefish. Sturgeon are large, slow-maturing, long-lived, primitive fish found in large inland and coastal rivers and some lakes. White sturgeon are found in lower and upper waters, sometimes hundreds of miles inland. Green sturgeon are usually found in the lower parts of estuaries. Adult sturgeon of the genus Acipenser, with the sole exception of lake sturgeon, are anadromous. They typically winter in the ocean and migrate to coastal rivers when the water warms above 54°F. Sturgeon also use peak spring river flows as a cue to migrate. Most sturgeon remain in brackish water for several days before migrating upstream or into the ocean. They then migrate hundreds of miles upstream, reach gravel bars, and spawn in high-speed currents. Several males spawn with each female, and the eggs stick to the gravel. The eggs hatch and the fry are carried downstream to areas of lower current velocity. Adults then move downstream to summer habitat where they remain until fall.

Food and feeding habits

Most sturgeon are opportunistic feeders. Juveniles feed primarily on aquatic invertebrates, while adults may also consume shellfish, fish, and crayfish. Some species, such as the white sturgeon, are good predators and will happily eat other fish. Migratory adults of Acipenser, with the exception of white and lake sturgeon, do not usually feed in freshwater.

Reproduction

Sturgeon often do not become sexually mature until they are 6 years old, and in some areas until they are 10 or 12 years old. Sturgeon spawn periodically, every 2-6 years, depending on the species.