Meeting Abstract
Fish fins are highly flexible, which allows them to form complex shapes that can offer hydrodynamic performance benefits. The flexibility in their fins allow fish to be highly maneuverable, permitting behaviors such as obstacle avoidance, predator escape, and backwards swimming. Fins also serve a sensory role, with many sensory receptors embedded in the rays, but we know relatively little about how the sensory information affects the muscular control patterns. Our research focuses on the dorsal fin of bluegill sunfish, which has a soft posterior portion that functions during locomotion as a highly flexible control surface, and presumably also as a flow sensor. To quantify sensorimotor integration in the fin’s movements, we recorded activity in the dorsal inclinator muscles with and without a lidocaine treatment that numbs the sensory receptors. We quantified activity in the inclinator muscles and in red axial muscle during steady swimming at a low and high flow tank speed in three conditions: before fin numbing treatment, during fin numbing with lidocaine, and after lidocaine wash-out. During normal steady swimming, fish activate their dorsal inclinator muscles to stiffen their fins to resist lateral bending of the soft dorsal fin caused by resistive fluid forces imposed by the water. Activity of the dorsal inclinator muscles was variable when the fins were numb, with increased duration in each fin burst cycle, likely stiffening the fin. Our study shows that fish use sensory feedback for precise fin control during normal steady swimming, but without normal sensory inputs, they tend to stiffen the fin to make it more robust to mechanical perturbations.
