# Swimming Behavior of Percocypris pingi in the Wake of D-Shaped Obstacles: A Comparative Study of Single- and Dual-Fish Swimming in Complex Hydrodynamic Environments

## TL;DR

This study examines how single and paired fish of the species Percocypris pingi swim differently in the wake of D-shaped obstacles, revealing how they adapt to complex water flows.

## Contribution

The study reveals how dual-fish swimming adapts to hydrodynamic interference through formation changes, offering new insights into fish behavior in altered river environments.

## Key findings

- Single fish use the Kármán gait to efficiently harness vortex energy and improve swimming efficiency.
- Dual-fish groups maintain a fore–aft alignment to optimize wake utilization and resist vortices.
- Group swimming leads to mutual interference, prompting fish to adjust their patterns for better efficiency.

## Abstract

The changes in water flow caused by hydropower projects and river diversions have had a profound impact on aquatic ecosystems, especially due to artificial structures such as dams and bridge piers. This study investigates the swimming behavior differences between single and dual fish in the wake region behind a D-shaped obstacle, using Percocypris pingi as the experimental species. The results show that single fish efficiently utilize vortex energy through the Kármán gait, improving swimming efficiency, while the dual-fish group failed to maintain a stable Kármán gait, resulting in irregular swimming trajectories. However, the dual-fish group optimized wake utilization by maintaining a fore–aft linear alignment, improving swimming efficiency and resisting vortices. The conclusion indicates that mutual interference in group swimming affects swimming efficiency, with fish adjusting their swimming patterns to adapt to complex hydrodynamic conditions. By altering swimming formations, fish schools can adapt to the flow environment, offering new insights into the swimming behavior of fish and providing theoretical support for ecological conservation and hydropower project design.