3.4 Friday, Jan. 4 Body dynamics of larval fish - implications for the mechanics of large-amplitude swimming VAN LEEUWEN, J L ; MULLER, U K*; Wageningen University; California State University Fresno email@example.com
Body and center-of-mass dynamics are fundamental to the mechanics of locomotion. Experimental studies have shown that small swimmers and flyers are relatively strong, since they generate forces and torques that are large compared with their body weight. However, small organisms must overcome relatively high drag forces, so their locomotion is characterized by high thrust and low efficiency. In this study, we quantify the center-of-mass kinematics of zebrafish larvae from video recordings of C starts and cyclic swimming. During cyclic swimming, the larval tail produces high torques as part of thrust generation: torque correlates with tail velocity (rather than tail acceleration, or velocity of anterior body sections). Torque increases with swimming speed, as do kinetic energy and power output. A maximum power output of 20 W/kg is observed at swimming speeds of 0.2 m/s at tail beat frequencies of 100 Hz. This value approaches the maximum power of fast and superfast muscles. Strouhal number decreases with increasing speed and Reynolds number, from values above 2 at Re 100 to 1 at Re 1000, indicating that swimming efficiency increases with speed. Previous studies on C starts suggested that fish begin to translate in the preparatory phase (stage 1, formation of the “C”). Our data show that the center of mass moves outside the body during stage 1, but does not translate in the earth-bound frame of reference. Translation begins during the propulsive phase (stage 2). Translational kinetic energy during stage 1 is near zero; rotational kinetic energy is high during stages 1 and 2, indicating that the change of heading during a C start is the net result of the large torques generated during both stages. We did not find the previously reported inverse relationship between forward speed and turning angle.