Meeting Abstract
Fishes must swim effectively to catch prey, evade predators, and find shelter and mates. Since these behaviors are important for evolutionary fitness, understanding how mechanical forces are produced by a fish’s body and appendages can provide insight into the evolution of their present body forms. Traditionally, we have assumed that thrust production occurs by body movements pushing fluid rearward, creating areas of high pressure around the body that in turn push the fish forward. Yet, areas of low pressure are created in tandem with these high-pressure locales. For lampreys, the pulling forces arising from these low-pressure regions contribute significantly to total thrust, but for other fish species, the role of such pulling forces is not known. Here, we use a particle image velocimetry-based technique to calculate the pressure distributions around bluegill sunfish (Lepomis macrochirus) and brook trout (Salvelinus fontinalis) during steady, free swimming. From these pressure data, locomotor forces can be accurately estimated at high spatial and temporal resolution. We find that high and low pressure both contribute to thrust and drag production, and they do so in different patterns along the body. We demonstrate that these low-pressure-based thrust forces are distributed along the body and are not solely localized to the caudal region, which has been suggested to be where thrust is primarily generated in carangiform swimmers. These results show that fishes may simultaneously use a variety of mechanisms to produce forces. Developing a more complete understanding of these mechanisms may ultimately help illuminate how the requirements for effective force production constrains the evolution of fish body forms.
