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

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.