Dynamics of the Electroreceptors in the Paddlefish, Polyodon Spathula

Abstract

The paddlefish, Polyodon spathula, inhabits the major rivers of the Midwest and feeds on Zooplankton, such as the water flea Daphnia sp., in murky water where vision is of limited effectiveness. Small paddlefish capture the Zooplankton individually while adult paddlefish filter feed in large quantity. The paddlefish has evolved an elongated (about 1/3 the animal’s length) paddle-shaped rostrum which extends anterior to the head from just above the animal’s mouth. On both upper and lower rostrum surfaces and extending onto the head and opercular flaps, the skin contains numerous electrosensitive ampullae (Jørgensen et al.,, 1972), indicating the existence of an electrosensory system (New and Bodznick, 1984). It has been shown recently in this laboratory (Wilkens et. al.,., 1997) that the paddlefish feeding relies on electrosensory detection of the oscillating electric fields, characteristic of its planktonic prey, rather than relying on vision. The ampullary electro- receptors are innervated by primary afferents of the anterior lateral line nerves that project to the medulla through dorsal and ventral roots (New and Bodznick, 1984).