Effect of Total Dissolved Gas Supersaturation on Swimming Performance of Migratory Fish for Traversing Velocity Barriers

This study investigates the impact of total dissolved gas supersaturation (TDGS) on the swimming capabilities of migratory fish (S. prenanti), a common issue during high dam discharges in flood seasons. We assessed fish exposed to 130% TDGS for 2 hr, focusing on their swimming performance in a controlled environment. In our experiments, control group fish, utilizing prolonged swimming, showed reduced maximum distances as flow velocities increased from 3 to 10 BL/s (body length per second), covering distances between 1,285 and 119 BL. In contrast, TDGS-exposed fish achieved only 15%–95% of these distances. Under burst swimming conditions, control group fish also demonstrated a decrease in maximum distances with increasing flow velocity, achieving 280–124 BL, while TDGS-exposed fish reached just 48%–64% of these distances. Notably, the critical flow velocity (U_fcrit) for transitioning from prolonged to burst activity level was lower for the TDGS group (7.2 BL/s) compared with the control (9.8 BL/s). In open flume trials, TDGS-exposed fish displayed a stronger upstream swimming inclination beyond U_fcrit, indicated by quicker times, higher speeds, and shorter trajectories. This study provides novel insights into the adaptive swimming strategies and flow velocity responses of fish under TDGS stress.