Scientific Name: Polyodon spathula
Common Names: paddlefish, spoonbill, shovelnose
In Ohio, paddlefish are native to Lake Erie and the Ohio River and its tributaries. Although population densities have declined, they are still found in the Ohio River and some of the major tributaries. These fish have a distinctive appearance, with the presence of a long snout, deeply forked tail, and are gray in color. The paddlefish’s genus name, Polyodon, comes from a Greek word meaning “many tooth” and refers to their gill rakers (Texas Parks and Wildlife). Their extensive gill rakers are used for filter feeding. Although paddlefish can reach large sizes (over 100 pounds), they feed primarily on plankton. The paddlefish’s species name, spathula, derives from a Latin word meaning “spatula” or “blade.”
The function of the paddlefish’s unique rostrum (paddle) has long been debated. Lon Wilkens, at the University of Missouri, St. Louis, conducted research that documented how the paddle functions. With the paddlefish reaching such large sizes, it is obvious that it must be extremely efficient at capturing mass amounts of food. Being primarily a river dweller, the paddlefish lives in a murky, harsh environment. They are known to have poor eye sight, so to thrive in river environments their other senses must be extraordinary. The results of Lon Wilkens’ research show paddlefish are most likely use their long snout to detect prey.
Paddlefish feed on plankton, such as the water flea (Daphnia), that have been found to emit weak electrical signals. It appears the rostrum is a highly developed electro-receptor that can detect signals of less than 1/100th of one 1-millionth volt per centimeter. Laboratory studies verified that juvenile paddlefish will strike at electrodes placed in the water that emit currents similar to currents emitted by plankton. The response was verified by conducting the experiments in the dark, proving that the strike was not visually triggered. It was concluded that the paddlefish’s rostrum is a highly sensitive “antenna” that aids the fish in not only feeding, but also navigation. When metal objects were place in the swim path of paddlefish, they routinely avoided them. However, when plastic objects were placed in their path, they usually collided with them.
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