Meeting Abstract
Fish generate propulsive forces by bending their bodies back and forth using their muscles. During this motion, their bodies interact mechanically with the fluid around the fish. Therefore, the mechanical properties of their bodies are important for determining how effectively these muscle forces can be converted into whole-body propulsive forces. In this study, we measured the whole-body visco-elastic mechanical properties of pithed bluegill sunfish, Lepomis machrochirus. We used an oscillatory bending apparatus in which the tail of the fish was connected to a servomotor, while the other end was attached to a six-axis force transducer. Electrodes were inserted into the red muscle bands on the left and right side of the fish. The bodies were then bent back and forth at 3 Hz and an amplitude of 5 degrees while we altered muscle activation phases (-30%, -15%, and 0%) and duty cycles (20%, 30%, and 40%). Muscle activations were performed based on previous observations (underlined) made by Schwalbe et al. (2019). We aim to answer the following questions: 1) how do whole-body visco-elastic properties change between active and passive bending cycles?, and 2) do naturally observed muscle activation phases and duty cycles result in higher body stiffness? We found that body torques, local flexural stiffness, and local damping were highest at 0% phase, and were lowest at -30% phase. Passive stiffness and damping tended to be lower than active measurements. Surprisingly, changes in duty cycle did not result in any changes to the visco-elastic properties measured in this study.
