American Paddlefish

The American paddlefish (Polyodon spathula) is one of only two surviving species in the ancient family Polyodontidae, the other being the now-extinct Chinese paddlefish. Native to the Mississippi River drainage of the central United States, it is one of the largest and most primitive freshwater fish in North America, with a lineage stretching back tens of millions of years. Its most striking feature is a long, flattened, paddle-shaped snout (rostrum) used to detect plankton. Populations have declined due to damming and habitat fragmentation, and the species is now considered vulnerable across much of its range, with active conservation and stocking programs in several states.

The paddlefish is unmistakable among North American freshwater fish:

• Long, flat, paddle-shaped rostrum making up roughly a third of body length
• Smooth, scaleless gray to bluish-gray skin (a small patch of scales occurs only near the tail)
• Huge, wide mouth used for filter feeding, often held open while swimming
• Deeply forked, shark-like heterocercal tail
• Small eyes and a cartilaginous, shark-like skeleton Its combination of paddle snout and scaleless body separates it instantly from sturgeons, which have bony scute rows and shorter conical snouts. Juveniles have proportionally shorter, rounder snouts that lengthen and flatten noticeably as the fish matures into adulthood.

Paddlefish inhabit large, slow-moving rivers, oxbow lakes, and reservoirs throughout the Mississippi, Missouri, and Ohio river systems, ranging from Montana to the Gulf of Mexico. They favor warm, turbid water with abundant plankton and avoid fast, rocky headwater streams. Dams and river channelization have fragmented many historic populations by blocking access to spawning grounds. The species requires long stretches of connected river with seasonal flow pulses to complete its life cycle, and it is largely absent from small, isolated, or heavily impounded waterways within its former range.

Paddlefish swim slowly with mouths agape, filtering zooplankton from the water column using comb-like gill rakers, guided in part by electroreceptors on the rostrum that detect faint electrical fields from prey swarms. They undertake seasonal upstream migrations in spring to spawn over clean gravel bars during rising, flowing water. Individuals are long-lived, sometimes exceeding 30 years, and mature slowly, not reproducing until around age 7-10. They tend to be loosely aggregated rather than tightly schooling, and as efficient plankton consumers they play an important role in transferring energy through large river food webs.