Meeting Abstract
Pressure is a fundamental modality through which aquatic organisms like fish interact with their surrounding environment. In particular, pressure fields are the source of the forces that allow a fish to move. To swim, a fish passes a sinusoidal wave of bending down its body, or moves its fins, creating localized regions of high and low pressure in the water adjacent to the body. By shaping the development and transport of these pressure gradients with their kinematics, fish produce the forces needed for swimming, turning, and station-holding. Despite the close coupling of pressure and forces, few studies have experimentally measured pressure fields, owing to the difficulty in obtaining these measurements, especially on fine spatial and temporal scales around the entire fish body. This has greatly limited our ability to examine real-time locomotor forces. Here, we use flow velocity vector fields, measured using digital particle image velocimetry, to calculate pressure fields in the water surrounding freely moving bluegill sunfish (Lepomis macrochirus), swimming steadily in a flow tunnel. From these, we derive instantaneous forces acting along the fish’s body. We then examine the patterns of pressure and force distribution, and how they change as the bluegill shifts from pectoral fin propulsion at low speeds to body-caudal fin propulsion at high speeds. Future analyses will seek to understand how these fluid-body interactions lead to the flow structures shed into the wake, and how forces are modified during maneuvering.
