The
American paddlefish (
Polyodon spathula, also known as a
Mississippi paddlefish,
spoon-billed cat, or
spoonbill) is a species of
ray-finned fish. It is the last
living species of
paddlefish (Polyodontidae). 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. 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. 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. 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 highly
derived fish because it has evolved specialised adaptations such as
filter feeding. Its rostrum and cranium are covered with tens of thousands of sensory receptors for locating swarms of
zooplankton, its primary food source. 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.
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. It commonly inhabited large, free-flowing rivers,
braided channels, backwaters, and
oxbow lakes throughout the Mississippi River drainage basin, and adjacent
Gulf Coast drainages. Its peripheral range extended into the
Great Lakes, with occurrences in
Lake Huron and Lake Helen in Canada until about 1917. American paddlefish populations have declined dramatically primarily because of
overfishing,
habitat destruction, and
pollution.
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. Naturally occurring American paddlefish populations have been
extirpated from most of their peripheral range, as well as from
New York,
Maryland,
Virginia, and
Pennsylvania. They have been
reintroduced in the
Allegheny,
Monongahela and
Ohio river systems in western Pennsylvania. However, their current range has been reduced to the Mississippi and
Missouri River tributaries and
Mobile Bay drainage basin. American paddlefish are currently found in twenty-two states in the U.S., and are protected under state, federal and international laws. (
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