Field kinematics of intermittent swimming in bluegill sunfish <i>(Lepomis macrochirus)</i>—pelagic locomotion and littoral maneuverability

Abstract Objectives Locomotion is essential for the survival of animals. Fishes have evolved mechanisms to minimize the cost of transport. For example, Bluegill Sunfish (Lepomis macrochirus) employ intermittent swimming, which involves swimming at relatively slow speeds with short propulsive bursts alternating with gliding episodes. This typically involves axial undulation powered by slow-twitch muscle, either with or without pectoral fin usage. The propulsive bursts are at higher tailbeat frequencies than observed for a given average speed with constant propulsion, and muscle physiology experiments show that the propulsive bursts produce relatively high power, while the glide reduces fatigue relative to continuous activity. However, Bluegill encounter complex 3D in-shore habitats, in which an intermittent swimming gait may enable successful capture of habitat-specific prey. Methods Field observations of Bluegill Sunfish were made via underwater videography in Lake Waban, Massachusetts. Key Findings In both pelagic and littoral habitats, Bluegill employed intermittent swimming. This provided the maneuverability and muscle activity needed to capture prey items suspended in the water column and enabled effective prey detection and maneuverability for feeding on sessile invertebrates in dense vegetation. Radio telemetry studies demonstrated that bluegill moved regularly between the pelagic and the littoral. Conclusion In both zones, intermittent swimming may provide both energetic and foraging advantages.