Oscillation and dispersion of live grass carp egg settlement in static water: Laboratory experiments and theoretical models

Abstract Full understanding of the settling process of drifting fish eggs in static water is crucial for improving predictions of fish egg drift in rivers, which can inform reservoir operations by incorporating the ecological requirements of fish. However, current understanding of the settling process remains limited. Observations and analysis of live grass carp egg settlement in static water, with a video capture technology and wavelet analysis, have improved understanding. Results reveal that microscale oscillation and dispersion occur during the settling process. The oscillating velocities of eggs had periods of 0.113 s in longitudinal and 0.135 s in vertical, with oscillating angles around 1.13°. The maximum position differences among eggs after stably settling for 14 s were 25.0 mm in vertical and 4.2 mm in longitudinal. Mechanical models were then established and employed to elucidate two settling phenomena. Simulated results revealed that microscale oscillation was related to biological attributes (the egg specific gravity and diameters of the egg and embryo), special inner structure of the live egg and random hydraulic disturbance of the surroundings. Dispersion was mainly caused by the difference between eggs (diameter and specific gravity). This work furthers understanding and forecasts of fish egg drift in rivers, from which river engineers and managers can better estimate the locations of fish spawning sites, calculate ecological water requirement, and designate ecological conservation areas.