A computational fluid dynamics (CFD) study on changes in dissolved oxygen levels during a tidal cycle in a non-conventional finfish aquaculture structure

Abstract

This study examined the effects of i) the maximum current speed, ii) slack tide length, and iii) tidal cycle length, on the Dissolved Oxygen (DO) inside a non-conventional finfish aquaculture structure with varying fish stocking densities between 5 and 30 kgm⁻³, using Computational Fluid Dynamics (CFD). The three volume fractions of interest for finfish to survive and thrive are classified as lethal (DO < 30% of ambient DO); sub-optimal (30% < DO ≤ 70%); and optimal (DO > 70%). When the fish stocking density was 30 kgm⁻³ and the maximum current speed halved from 0.1 to 0.05 ms⁻¹, the lethal time (the time that the lethal DO fraction ≥0.5 of volume structure) increased from 0 to 72 min. Increasing slack tide length from 0 to 60 min increased the lethal time fraction from 0 to 66 min. Increase in tidal length (from semidiurnal to diurnal) resulted in an increase of lethal time from 0 to 63 min. During lower DO supply and greater DO consumption, the lethal fraction dominated the sub-optimal fraction. We recommend that the fish stocking density should be reduced in locations where tide dynamics result in lower DO conditions, to avoid lethal conditions inside the structure.