Swimming behaviour of downstream migrating carp in accelerating flows

Abstract

The downstream migration of fish is impacted by accelerating flow. This study coupled computational fluid dynamics (CFD) modelling and laboratory observations to investigate the effects of two different accelerating flow hydrodynamics on the swimming behaviours of two fish species. The silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis) were chosen as target fish species and four hydrodynamic parameters were selected as main indicators to affect fish swimming behaviours. Four specific swimming behaviours were classified in the contraction flume based on fish downstream trajectories. The results indicated that high accelerating flow, low turbulent kinetic energy (T_ke) and shear stress generated the symmetric distribution of fish along two boundaries of the contraction flume. It also indicated that discharge increase would increase the fish entrainment risk from intakes to diversion pipe, while two fish species exhibited different swimming behaviour patterns. Velocity and velocity gradient had more significant effects than other hydrodynamic parameters on fish swimming strategies. There was mutual compensation among fish tail-beat frequency, angle and amplitude. The results illustrated the relationship between the swimming behaviours and hydrodynamics, which could contribute to understanding the fish downstream migration behaviours in accelerating flow.

KEYWORDS:

• Accelerating flow
• bighead carp
• downstream migration
• hydrodynamics
• silver carp
• swimming behaviour

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

We are grateful for financial support from the National Key Research and Development Program of China [2022YFC3202002 & 2023YFC3205900]. The Guizhou Province Science and Technology Project [(2024)116]. The Ecological Monitoring and Restoration in Dongfeng Lake and Liuchong River Basin [No. 20231]. The Bijie Talent Team of Biological Protection and Ecological Restoration in Liuchong River Basin [No. 202112] and Cooperative Research Project of Sichuan Water Resources Department [SKY-2020-SJZX-16].