NELSON, M.E.: Active Electrosensory Signal Acquisition in Weakly Electric Fish

Animals can actively influence the content and quality of sensory information that they acquire from the environment by motor control of peripheral sensory surfaces. Black ghost knifefish (Apteronotus albifrons) are nocturnal hunters that feed on insect larvae and small crustaceans in the freshwater rivers of South America using an active electric sense. For the past several years, our laboratory has been carrying out behavioral, electrophysiological, and computational studies of prey capture behavior in these animals. Infrared video and 3-D model-based tracking methods are used to obtain quantitative information on body position and conformation as knifefish hunt for small prey (Daphnia magna) in the absence of visible cues. Computer modeling techniques are then used to reconstruct spatiotemporal images of electroreceptor activation. In these studies, we have observed and characterized an electrosensory orienting response, whereby the fish rolls its body toward the prey in order to bring the prey above the dorsal midline. We speculate that this dorsal centering of the prey may facilitate spatial localization by allowing comparisons between electroreceptor activation the left and right sides of the body. We suspect that the dorsal roll behavior also has a biomechanical basis related to the hydrodynamic constraints associated with the knife-like shape of the animal. The electrosensory specialization of the dorsal body surface and the dorsal roll behavior in Apteronotus may reflect a combined optimization of sensory and biomechanical constraints on the prey capture task. Supported by: NIMH R01MH49242