Meeting Abstract
The bodies of fishes are composed of flexible materials that interact mechanically with the fluid around the fish. While the behavior and mechanics of fish swimming have been studied for decades, few studies have investigated the role of internal body mechanics in swimming performance. Fish generate propulsive forces by activating muscles that bend their bodies from side to side. The internal viscoelastic body mechanics therefore determine how effectively these muscle forces can produce whole-body propulsive forces. In this study, we measured the viscoelastic mechanical properties of the bodies of bluegill sunfish, Lepomis machrochirus, over a range of sizes, from 65 to 170 mm SL. We used an oscillatory bending apparatus in which fish were connected to a servomotor, while the other end of the fish were attached to a six-axis force transducer. The bodies were then bent back and forth at different frequencies (1 – 7 Hz) and amplitudes (2.5, 5, 7.5, 10, 12.5, and 15 degrees) while body torques were measured with the force transducer. We made these measurements at two body regions: between the 1st and 3rd dorsal fin ray and between the 1st and 3rd anal fin ray. We aim to answer several questions, including (1) does the fish body have a resonant frequency?, (2) do the body regions differ mechanically?, and (3) How do these properties change across ontogeny? We found that body torques increased with increasing amplitude, but remained unchanged across frequencies, indicating that the body does not have a resonant frequency in the range of normal swimming frequencies. Local flexural stiffness on the other hand increase with frequency, but remained unchanged with increasing amplitudes. Both body torques and local flexural stiffness increased with increasing body size.
