Impact of the internal flow in a jet fish pump on the fish

The present paper describes a jet fish pump designed to safely convey fish in the aquatic industry due to its simple structure and reduced tendency to cause mechanical injury. High-speed imaging, physiology investigations and CFD simulations are used to demonstrate the impacts of the flow on the grass carp during transport in the jet fish pump for various operating conditions. The results show that none of the tested fish were dead, had organ injuries or had swimming problems after passing through the jet fish pump. The respiratory rates and most of the blood indexes of the tested fish were affected by the flow field in the pump, but they were able to recover to normal levels after just 24 h. The surface injuries such as descaling and operculum injuries were mainly caused by recirculation flows, shear flows and pressure gradients. Further analyses indicated that bruising was caused by the flow direction changes, with cavitation potentially causing eye injuries. A deflection number, Cd, was proposed to describe the amount of flow direction changes for various operating conditions in the jet fish pump. The results show that, even though shear flows and pressure gradients are inevitable, the jet fish pump operating conditions can be optimized to reduce the risk of fish injuries. Recirculation regions and intensive cavitation should be avoided since they may cause serious injuries in the fish, reduce the fish transport rate and reduce the flow efficiency. These results provide a basis for improved jet fish pump designs.