One recent study demonstrated that electrosensory receptors in paddlefish rostrum can detect weak electrical fieldsand suggested that paddlefish use their rostrum as an electrosensory "antenna" to detect zooplankton. Although the rostrum may aid the paddlefish in finding concentrations of zooplankton for feeding, some studies have shown that paddlefish with missing or severely damaged rostrums appear to be in good condition and grow similarly to those paddlefish with healthy, intact rostrums.
 

Paddlefish are one of the largest freshwater fishes in North America, commonly reaching 5 feet or more in length and 60 pounds in weight. The largest paddlefish on record was caught in Iowa and weighed 198 pounds. Although determining their age is difficult, some studies have recently estimated that paddlefish may live in excess of 50 years.

Paddlefish were once common in the fish assemblage in central U.S. rivers, but populations have declined in many systems. Paddlefish populations have been negatively affected by overharvest, sedimentation, and river modifications. Dams in particular have had an adverse affect on paddlefish because they alter traditional paddlefish habitats and can block spawning migrations and other movements. Paddlefish populations dramatically declined from overfishing after the turn of the last century. Concern for paddlefish stocks has recently risen because the collapse of most sturgeon stocks in the world has fueled increased demand for paddlefish eggs for the lucrative caviar trade.
 

Paddlefish are not closely related to sharks, but they do share some common characteristics including a skeletonprimarily composed of cartilage, and a deeply forked, abbreviate heterocercal tail fin (the top fin lobe is slightly larger than the lower fin lobe). Paddlefish are one of the oldest fishes, with fossil records dating their first appearance at 300 to 400 million years ago (about 50 million years before the first dinosaurs appeared). The North American paddlefish (Polyodon spathula) has only one other species as a member of the same family. The Chinese paddlefish (Psephurus gladius) is found in the Yangtze River and has a cone-shaped snout rather than the long, paddle-like snout (known as a rostrum) of the North American paddlefish.