Effects of Total Dissolved Gas Supersaturation on the Swimming Behavior of Bighead Carp (Hypophthalmichthys Nobilis) in Response to Various Flow Velocities in an Experimental Vertical Slot Fishway

Abstract

The operation of dams in the Yangtze River basin has historically induced severe total dissolved gas supersaturation (TDGS) due to flood discharges, adversely affecting the swimming behavior of resident fish. This disruption is compounded by habitat fragmentation resulting from numerous dam constructions, making fish passage facilities a critical mitigation strategy. This study assessed the swimming performance of bighead carp in a controlled vertical slot fishway under varied flow velocities of 0.2, 0.25, and 0.3 m/s after two hours of exposure to TDG supersaturated water. The results demonstrated that increased TDG levels and flow velocities significantly reduced fish passage efficiency. Specifically, passage success rates decreased to 61%, 48%, 37%, and 37% at TDG levels of 100%, 110%, 120%, and 130% respectively, at a flow velocity of 0.2 m/s. At flow velocities of 0.2, 0.25, and 0.3 m/s with 100% TDG supersaturated water, success rates were 61%, 53%, and 47%, respectively. Moreover, heightened TDG levels and increased flow velocities notably extended passage times in the intermediate pool. Both TDG levels and fishway flow velocities significantly influenced the chosen passage routes for fish. Preferences for flow velocities were notably impacted by TDG levels, while preferences for turbulence kinetic energy (TKE) were affected by both TDG levels and the velocities of the fishway flows. This study developed an evaluation method to assess the adverse effects of TDGS based on critical parameters: passage success, time, path, and hydraulic preferences. It further discussed potential mitigation measures through adjustments in fishway flow velocities to counteract TDGS-related impacts. This research offers valuable insights into ecological management and operational adjustments during dam flood discharges and fishway management.

Keywords: TDG supersaturation, Swimming performance, Vertical slot fishway, Bighead carp