Settling and transport properties of grass carp and silver carp eggs in the water-hardened phase: Implications for resource protection and invasion control during early life period

Abstract

Grass carp and silver carp eggs have no swimming ability in the water-hardened phase and need to drift for tens or even hundreds of hours before complete incubation. A full comprehensive understanding of the settling and transport properties of eggs is crucial for the resource protection and invasion control of Four Major Chinese Carps (FMCCs) during their early life stages. Artificial eggs have been used extensively in previous field and flume experiments; however, our understanding of the settling and transport properties of real eggs in the water-hardened phase remains limited. In the present study, a series of column and flume experiments were conducted in stagnant and moving water, respectively. In light of the differences in settling characteristics, caution should be exercised when applying research results obtained from artificial eggs having the closest diameter and specific gravity as real eggs. Compared with grass carp and silver carp eggs in the water-hardening phase, egg diameters in the water-hardened phase were 36% and 33% greater, respectively, and egg hydrostatic settling velocities were 31% and 40% lower, respectively. Significant interspecific differences between the two species exist in terms of egg size and hydrostatic settling velocity. Based on linear mixed effects analysis of dominant transport trajectories and regression analysis between suspending rate and flow velocity, 0.30 m/s can be considered as critical drifting velocity in uniform flow. Adaptive management schemes are discussed to promote resource protection and invasion control of FMCCs during the early life stages. The results of the present study enhance our understanding of drifting egg movement and provide insights that could facilitate the comprehensive management of FMCCs.