They have been reintroduced in the Allegheny, Monongahela and Ohio river systems in western Pennsylvania. Naturally occurring American paddlefish populations have been extirpated from most of their peripheral range, as well as from New York, Maryland, Virginia, and Pennsylvania. Poaching has also been a contributing factor to its decline and is liable to continue to be so as long as the demand for caviar remains strong. American paddlefish populations have declined dramatically primarily because of overfishing, habitat destruction, and pollution. Its peripheral range extended into the Great Lakes, with occurrences in Lake Huron and Lake Helen in Canada until about 1917. It commonly inhabited large, free-flowing rivers, braided channels, backwaters, and oxbow lakes throughout the Mississippi River drainage basin, and adjacent Gulf Coast drainages. The American paddlefish is native to the Mississippi river basin and once moved freely under the relatively unaltered conditions that existed prior to the early 1900s. The only other species of paddlefish that survived to modern times was the Chinese paddlefish ( Psephurus gladius), last sighted in 2003 in the Yangtze River in China and considered to have gone extinct no later than 2010. Its rostrum and cranium are covered with tens of thousands of sensory receptors for locating swarms of zooplankton, its primary food source.

The American paddlefish is a highly derived fish because it has evolved specialised adaptations such as filter feeding. It has been referred to as a freshwater shark because of its heterocercal tail or caudal fin resembling that of sharks, though it is not closely related. The American paddlefish is a smooth-skinned freshwater fish with an almost entirely cartilaginous skeleton and a paddle-shaped rostrum (snout), which extends nearly one-third its body length. Fossil records of other paddlefish species date back 125 million years to the Early Cretaceous, with records of Polyodon extending back 65 million years to the early Paleocene. This family is most closely related to the sturgeons together they make up the order Acipenseriformes, which are one of the most primitive living groups of ray-finned fish. It is the last living species of paddlefish (Polyodontidae). The American paddlefish ( Polyodon spathula, also known as a Mississippi paddlefish, spoon-billed cat, or spoonbill) is a species of ray-finned fish. Accipenser lagenarius (sic) Rafinesque 1820.

Fish with platypus tail