The American paddlefish, Polyodon spathula, also called the Mississippi paddlefish or spoonbill is a paddlefish living in slow-flowing waters of the Mississippi River drainage system. It appears to have been extirpated from Lake Erie and its tributaries. They are closely related to the sturgeons. This large Chondrostean freshwater fish may grow to 220 cm (7 feet) and weigh up to 100 kg (220 pounds). The American paddlefish takes its common and scientific names from its distinctive snout, which is greatly elongated and flattened into a paddle shape. The American paddlefish is believed to use sensitive electroreceptors on its paddle to detect prey, as well as to navigate while migrating to spawning sites. The American paddlefish feeds primarily on zooplankton but also feeds on crustaceans and bivalves. Polyodon spathula is one of two living species of Paddlefish; the other is the possibly extinct Chinese Paddlefish, Psephurus gladius.
Though the American paddlefish was once common throughout the Midwest, overfishing and habitat changes have caused major population declines; both the meat and fish roe of Polyodon spathula are desirable as food. Dams and other barriers can prevent the fish from recolonizing places where they once occurred and can deny them access to important critical habitats such as spawning areas. Until about 1900, the species was also found in Lake Erie and in river systems tributary thereto in the U.S. and Canada. Invasive species such as zebra mussels have reduced the number of zooplankton in the Great Lakes to such low levels that any hypothetical reintroduction program would seem likely to fail. Recently, paddlefish were spotted in the Danube river. It has not been determined whether these fished escaped from Romanian or Bulgarian fish farms during the 2006 European floods, or whether they were let into the Danube earlier and matured in the river.
The American paddlefish remains a popular sports fish in those parts of its range where populations are sufficient to allow harvesting. Since they are filter-feeders, paddlefish will not accept bait or lures and must be caught by snagging. Several states, including Missouri, have enacted stocking programs for these fish in reservoirs where the resident populations were low or nonexistent, or in areas where historical populations are no longer naturally sustainable. Paddlefish roe is occasionally sold as “American Sevruga Caviar”.