Meeting Abstract

2.2  Friday, Jan. 4  Quantifying center of mass motion in swimming fishes LAUDER, G.V.*; XIONG, G.; Harvard Univ. glauder@oeb.harvard.edu

Movement of the center of mass (COM) during locomotion is a key parameter that is crucial for understanding the dynamics of movement in animals. Many studies of terrestrial locomotion have focused on motion of the COM during walking and running, but to our knowledge there is little information on how the COM moves during fish swimming, and no data on whether different patterns of body bending produce differences in COM motion. In this study we present an analysis of COM oscillations in steadily swimming fishes. Using the particle image velocimetry (PIV) method commonly used for flow visualization to instead track patterns on the body, we estimated COM movement of three fish species and swimming types: carangiform and labriform (sunfish, Lepomis macrochirus), anguilliform (eels, Anguilla rostrata), and gymnotiform (knifefish, Notopterus chitala). We estimated COM motion in three dimensions (x: surge, y: sway, z: heave) and at three swimming speeds (0.5, 1.0, and 1.5 L/sec). Surge and sway COM oscillation magnitudes (peak to peak) were in the range of 0.4 to 1.5 mm (for fish of about 20 cm total length). Sway COM increased as swimming speed increased for bluegill and knifefish, but not for eels. Surge COM did not change with swimming speed and was largest for bluegill and smaller for both eels and knifefish. The COM was found to oscillate with twice the tail beat frequency. A log-log plot of COM oscillation cubed versus body mass for different animals shows positive allometry with a slope of 1.4, and fish COM oscillations fall significantly below this line indicating that fish have lower COM oscillations than terrestrial animals. Locomotion using body bending may reduce COM oscillation magnitudes compared to limbed terrestrial locomotion using inverted pendulum or mass-spring mechanisms.