The effect of oxygen saturation on the growth and feed conversion of Atlantic halibut (Hippoglossus hippoglossus L.)

Juvenile Atlantic halibut (40.5 ± 9.1 g mean initial body mass ± SD) were reared at five different levels of oxygen availability (57%, 84%, 100%, 120%, and 150% of air saturation) for 94 days. The availability of oxygen significantly affected the growth rate of the fish while feed conversion was not significantly different. The final size of fish reared at 57% of air saturation was significantly lower than in groups reared at 100% to 150% of air saturation and the specific growth rate (SGR) in the 57% group over the 94 day period was significantly lower than in all other groups. The increase in biomass was 45% higher in the group exposed to 100% of oxygen saturation than in the group reared at 57% saturation. The group reared at 84% of air saturation was intermediate and the final size of this group was significantly different from fish reared at either 57% or 100%–150% of air saturation. There was no significant difference in the growth trajectories of fish reared at 100%–150% of air saturation but they were significantly different from those of fish reared at either 57% or 84% saturation. This suggests that the growth of halibut is progressively increased when the oxygen saturation is increased from 57% to 100% while further increase in oxygen saturation does not improve the growth rate. When oxygen saturation was increased, the blood pH increased as did the partial pressure of CO2, total concentration of CO2 and bicarbonate in blood. This change is likely a result of reduced ventilation rate with increased oxygen saturation. The results challenge the common recommendation that 60%–80% oxygen saturation is adequate to support maximum growth of fish. The results of the present study suggest that there may be an advantage for halibut farmers to increase the oxygen availability from the recommended 60%–80% oxygen saturation up to 100%.