A laboratory investigation of the transport mechanism of floating fish eggs: A case study of Asian carps

The transfer mechanism of fish eggs in water after spawned is assumed to cause the most intense impact on their hatching rate. Settling characteristics are different depending on the physical and biological properties (such as density, diameter and surface viscosity). In this study, the terminal settling velocities of the floating eggs of four carps at different water hardening stages were measured. The terminal settling velocities of the eggs gradually decreased with water hardening process. The terminal settling velocity of the eggs of bighead carp was highest, followed by black carp, silver carp and grass carp. Subsequently, an empirical formula describing the relationship between the drag coefficient and the Reynolds number was developed. The applicability of this formula was investigated in drifting experiments. We proposed a formula for calculating the drag coefficient of floating fish eggs. The drag coefficient formula of the floating fish eggs is suitable for the Reynolds numbers below 490. At Reynolds numbers >490, the drag coefficient was about 0.12. The results show that floating fish eggs differ significantly from other solid particles in their behavior and an own formula is necessary. This is the first study on the drag coefficient of the floating fish eggs. It further provides new insight on the movement of floating fish eggs in water and can be used in numerical simulation to describe the transport of floating fish eggs, essential for carp protection.