| Polyodon spathula|
(Walbaum in Artedi, 1792)
American paddlefish (Polyodon spathula) are basal ray-finned fish closely related to sturgeons in the order Acipenseriformes. Fossil records of paddlefish date back over 300 million years, nearly 50 million years before dinosaurs first appeared. American paddlefish are smooth-skinned freshwater fish commonly called paddlefish, but are also referred to as Mississippi paddlefish, spoon-billed cats, or spoonbills. They are one of only two extant species in the paddlefish family, Polyodontidae. The other is the critically endangered Chinese paddlefish, Psephurus gladius, endemic to the Yangtze River Basin in China. American paddlefish are often referred to as primitive fish, or relict species because they retain some morphological characteristics of their early ancestors, including a skeleton that is almost entirely cartilaginous, a paddle-shaped rostrum (snout) that extends nearly one-third their body length, and a heterocercal tail or caudal fin, much like that of sharks. American paddlefish exhibit synapomorphy because they have evolved adaptations for filter feeding. Their rostrum and cranium are covered with tens of thousands of sensory receptors for locating swarms of zooplankton, which is their primary food source.
American paddlefish are native to the Mississippi River Basin and once moved freely under the relatively natural, unaltered conditions that existed prior to the early 1900s. They commonly inhabited large, free-flowing rivers, braided channels, backwaters, and oxbow lakes throughout the Mississippi River drainage basin, and adjacent Gulf drainages. Their peripheral range extended into the Great Lakes, with occurrences in Lake Huron and Lake Helen in Canada until about 90 years ago. American paddlefish populations have declined dramatically primarily because of overfishing, habitat destruction, and pollution. Poaching has also been a contributing factor to their decline and will continue to be as long as the demand for caviar remains strong. Naturally occurring American paddlefish populations have been extirpated from most of their peripheral range, as well as from New York, Maryland, Virginia, and Pennsylvania. The current range of American paddlefish has been reduced to the Mississippi and Missouri river tributaries and Mobile Bay drainage basin. They are currently found in twenty-two states in the U.S., and those populations are protected under state, federal and international laws.
Taxonomy, etymology and evolutionEdit
American paddlefish are closely related to sturgeons in the order Acipenseriformes, an order of basal ray-finned fishes that includes sturgeon and paddlefish, several species of which are now extinct. Paddlefish are among the oldest of fishes as evidenced in the fossil record which dates their first appearance approximately 300 to 400 million years ago, almost 50 million years before the dinosaurs.