Mechanics of propulsion by multiple fins: kinematics of aquatic locomotion in the burrfish ( Chilomycterus schoepfi )

Abstract

Locomotion in tetraodontiform fishes (puffers and relatives) involves the use of multiple fins for propulsion during swimming. A variety of tertraodontiform swimming modes have been defined, but the contributions of pectoral, dorsal, anal, and caudal fins to the propulsion in these fish remain largely unknown. We used video analysis to study swimming behaviour of the striped burrfish ( Chilomycterus schoepfi ). Burrfish swam in a flow tank at speeds of 0.5–6.3 standard body lengths per second, during which all fins oscillated at all speeds. The oscillation frequency range of all fins was 2.1–9.2 Hz, increasing with velocity. Pectoral fins were always out of phase, usually by 180 degrees (alternate left and right beats). Reduced frequency parameters for all fins were high (0.65–12.1) indicating that acceleration reaction is the dominant mechanism of thrust. Phase lag between anal and caudal fins assumed three distinct states which suggests that burrfishes alter the patterns of fin motion in discrete stages analogous to gaits. Rapid oscillation of five fins in various degrees of asynchrony is a mechanism to produce relatively constant thrust from multiple periodic motions.