Scientists once believed paddlefish used their rostrums to excavate bottom substrate, but have since determined with the aid of electron microscopy that paddlefish rostrums are covered in electroreceptors called ampullae. These ampullae are densely packed within star-shaped bone projections that branch out from the rostrum. The electroreceptors can detect weak electrical fields which not only signal the presence of prey items in the water column, such as zooplankton which is the primary diet of the American paddlefish, but they can also detect the individual feeding and swimming movements of zooplankton's appendages. Paddlefish have poorly developed eyes, and rely on their electroreceptors for foraging. However, the rostrum is not the paddlefish's sole means of food detection. Some reports incorrectly suggest that a damaged rostrum would render paddlefish less capable of foraging efficiently to maintain good health. Laboratory experiments, and field research indicate otherwise. In addition to electroreceptors on the rostrum, paddlefish also have sensory pores covering nearly half of the skin surface extending from the rostrum to the top of the head down to the tips of the operculum (gill flaps). Therefore, paddlefish with damaged or abbreviated rostrums are still able to forage and maintain good health.
