Sub-acute effects of oxygen drops in landbased fish farms

Critically low dissolved oxygen levels may be a result of malfunctions in the water supply or the oxygenation systems in landbased fishfarms. In the present study Atlantic salmon (Salmo Salar) were exposed to decreasing oxygen levels to investigate the sub-acute effects of short-term oxygen stress on mortality, food intake and growth. In phase I the fish weight was 170 grams and the stocking density 7 kg/m³. 6 groups of fish were exposed to 3 mg/l once, twice, or three times or 2 mg/l once, respectively. In phase II the fish weight was 350 grams. The fish groups were exposed to 3 mg/l (stocking density 14 kg/m³ and 26 kg/m³) or 2 mgA (stocking density 13 kg/m³). In phase III the oxygen levels were the same as in phase II. The fish weight was 800–850 grams and the stocking density 34 kg/m³, 62 kg/m³ and 31 kg/m³ respectively. Preliminary results from phase I and II have shown that the oxygen stress did not result in any reduced growth or food intake nor did it result in increased mortality.