Abstract:

The formation of thrust and drag forces and the fluid dynamics around juvenile fish bodies during burst-and-coast swimming were investigated by using Particle Image Velocimetry (PIV) to capture fluid pressure distribution around juvenile grass carp (Ctenopharyngodon idella). The forces generated by positive and negative fluid pressures were calculated, and the ratio of thrust and drag forces as well as the swimming efficiency were compared across the head, middle, and tail regions of the fish body. Results indicate that during the bursting, thrust force is primarily generated by negative fluid pressure, whereas during coasting, the forward swimming mainly relies on the thrust generated by positive fluid pressure. Throughout the burst-and-coast cycle, the tail region contributes significantly to thrust generation (48.81% of total thrust), exhibiting the highest average swimming efficiency (77.28%±16.87%). Conversely, the middle region of juvenile grass carp experiences the highest drag force (67.82% of total drag).

Key words: juvenile grass carp, burst-and-coast, thrust, drag, particle image velocimetry(PIV), fluid pressure, swimming efficiency