Movement of surrogate semi-buoyant fish eggs in decelerating flow

The transport characteristics of semi-buoyant fish eggs significantly influence their drift, dispersal, and recruitment in rivers. Due to physical differences between eggs and flows, we hypothesize their motion is asynchronous with flow dynamics. Spherical surrogate particles mimicking real fish eggs in hydraulic properties were employed to investigate the three-dimensional movements in decelerating flows. Results indicated that surrogate eggs’ longitudinal velocity lagged approximately 22% behind flow velocities, while their vertical velocity was strongly flow-dependent. Eggs dispersed evenly laterally along the main flow axis. Furthermore, increased travel distance led to higher egg loss rates, attributed to gravitational settling and trapping effect. These outcomes provide valuable insights into evaluating the distribution patterns of semi-buoyant fish eggs during long-distance river drifting.