Sturgeon is the
common name for the 27 species of fish belonging to the family
Acipenseridae. Their evolution dates back to the
Triassic some 245 to 208 million years ago. The family is grouped into four genera:
Acipenser,
Huso,
Scaphirhynchus and
Pseudoscaphirhynchus. Four species may now be extinct. Two closely related species,
Polyodon spathula (paddlefish) and
Psephurus gladius (Chinese paddlefish, possibly extinct) are of the same order,
Acipenseriformes, but are in the family
Polyodontidae and are not considered to be "true" sturgeons. Both sturgeons and paddlefish have been referred to as "
primitive fishes" because their
morphological characteristics have remained relatively unchanged since the earliest
fossil record. Sturgeons are native to subtropical, temperate and sub-Arctic rivers, lakes and coastlines of
Eurasia and
North America. Sturgeons are long-lived, late-maturing fishes with distinctive characteristics, such as a
heterocercal caudal fin similar to that of
sharks, and an elongated spindle-like body that is smooth-skinned, scaleless and armored with 5 lateral rows of bony plates called
scutes. Several species can grow quite large, typically ranging 7–12 feet (2-3½ m) in length. The largest sturgeon on record was a
Beluga female captured in the
Volga estuary in 1827, weighing 1,571 kg (3,463 lb) and 7.2 m (24 ft) long. Most sturgeons are
anadromous bottom-feeders which migrate upstream to spawn but spend most of their lives feeding in
river deltas and
estuaries. Some species inhabit freshwater environments exclusively while others primarily inhabit marine environments near
coastal areas, and are known to venture into open ocean.
