Paddlefish - Polyodon Spathula
Etymology: Polyodon means many teeth, referring to the numerous gill rakers. Spathula means spatula, referring to the paddle-shaped snout.
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.
Paddlefish can be distinguished from other freshwater fish by the presence of a very large mouth, and a long, paddle-shaped snout (called a rostrum) that is about one third the length of the body. 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 are long-lived, with some fish known to exceed 30 years of age. Male Paddlefish generally mature at about 5 to 8 years and females at 8 to 12 years old. Large females can produce over a half-million eggs. Paddlefish spawn in early Spring when water temperatures approach the mid-50 F range. Females deposit their eggs over gravel bars in large free-flowing rivers. Immediately after being fertilized, the eggs sink to the bottom, sticking to the first object contacted, and hatch approximately seven to nine days later. Newly hatched young, which look very different from the adults, are carried by currents into areas where food is available. At about one month old, the young Paddlefish look very similar to the adults.
Early European explorers encountered this strange beast in North America's large rivers. Records of the Paddlefish date back to DeSoto's Expedition through the Southeast from 1539 to 1542. A writer known only as "A Gentleman of Elvas" wrote, "There was another fish called Pexe Pella (translated "peel fish"). Its snout was a cubit in length and the tip of its upper lip was shaped like a shovel."
Early investigators thought that Paddlefish used the rostrum to dig food items from the bottom or to dislodge them from vegetation. These ideas were refuted when Paddlefish were found to be filter feeders, straining zooplankton out of the water column. Gill arches are the predominant features seen inside the Paddlefish's mouth. Paddlefish swim with their mouth open, indiscriminately filtering the water. The gill arches have filaments on them called gill rakers that sieve the zooplankton organisms from the water.
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 over harvest, 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 over fishing after the turn of the last century. At one time, Paddlefish were one of the most commercially important fish in the Mississippi Valley, utilized for both their meat and caviar. Concern for Paddlefish stocks has recently risen because the collapse of most sturgeon stocks in the world has fueled an increase demand for Paddlefish eggs for the lucative caviar trade. Paddlefish are also prized as a sport fish in many parts of their range.