Meeting Abstract
Fishes swim by generating thrust through undulatory waves that propagate rostrocaudally down the body. Although many studies have investigated the hydrodynamic and fluid-structure influences on thrust production, relatively few have focused on the axial behavior of the fish body during swimming, especially over a range of biologically relevant speeds and beyond trailing-edge amplitude and frequency. The goal of this study was to revisit the relationships between propulsive wavelength and swimming speed and propulsive wavelength and body axial position. To this end, we performed flume-based experiments on rainbow trout (Oncorhynchus mykiss) swimming at 40 discrete speeds, ranging from 0.5-6.0 BL/s. Using a novel semi-automated tracking system implemented in the R computing environment, we amassed a dataset that includes over 80 thousand separate waveforms from five individual fish and this range of speeds. Our conclusive results indicate that: (1) undulatory wavelength increases as it passes through the body and (2) that this parameter has a non-linear, idiosyncratic relationship with swimming speed, both increasing and decreasing as much as 40% over different ranges of speed. Taken together, these results underscore the importance of both passive and active elements of the fish musculoskeletal system in modulating propulsive dynamics and that fishes may modulate body stiffness to optimize thrust under variable speed conditions.
