Changes to flow and turbulence caused by different concentrations of fish in a circular tank

Abstract

The effects of juvenile Atlantic salmon (Salmo salar) on flow and turbulence in a circular tank were investigated. Three fish sizes were studied (37.5 g, 82.5 g and 218 g) with between 268,050 and 318,000 fish in a 15 m diameter by 4 m deep tank (mean stocking densities of 15.3 kg m–3, 35.6 kg m–3, and 79.4 kg m–3). Flow in the enclosed tank was driven by the inflow from the water supply system and a degassing system. Velocities were measured using acoustic Doppler velocimetry with and without fish present. Dissolved oxygen was also measured, and the turbulent transport of dissolved oxygen calculated from eddy correlation. The average water velocity was reduced by 15% at low and medium stocking densities, and 57% at high stocking density. Turbulent kinetic energy, turbulence intensity, and turbulence dissipation rates were higher with fish than without. Fish altered the distributions of mean velocity, turbulence and oxygen, and increased the turbulent transport of oxygen. Vertical distributions of turbulence were consistent with echo-sounder derived fish distributions.