Meeting Abstract
Richard Bainbridge, in his classic 1958 paper, first provided quantitative data relating the frequency and amplitude of the tail of swimming fishes to the speed of locomotion. Many subsequent studies have built on his work, and suggested that there is a positive linear relationship between frequency and swimming speed, and that at moderate to higher swimming speeds tail beat amplitude changes little with speed. In our previous experiments with passive swimming foils, we observed non-linear effects of trailing edge frequency and amplitude as speed increases. These results stimulated us to revisit the Bainbridge relationships and to determine if freely-swimming fishes exhibit significant local deviations from linear as well as resonant amplitude effects as speed increases. We used automated high-resolution 3D tracking of tail beat amplitude and frequency to investigate how these parameters change with speed in three species (7 individuals total): largemouth bass (3), striped bass (3), and bluefish (1). A custom LabView program was used to automatically track the position of the tail tip and to compute frequency and amplitude at each tested speed. LabView control of speed in the recirculating flume allowed generation of a very high resolution data set for each individual. Statistical analysis confirmed that the frequency-speed plots exhibit significant local deviations from linear, and that there are “sweet spots” where speed increases with little change in frequency, and “sour spots” with a rapid increase in frequency with speed. We conclude that the relationship between frequency and speed in fishes exhibits many of the same phenomena observed for mechanical passive flapping panels.
