Effects of hyperoxia on behavioural and physiological variables in farmed Atlantic salmon (Salmo salar) parr

A controlled experiment mimicking Atlantic salmon (Salmo salar) pre-smolt farming conditions showed that fish exposed to 150 and 175% super oxygenated water produced higher levels of carbon dioxide with the subsequent decrease in water pH compared to control fish exposed to 100% O-2. At the 7th day of exposure the hyperoxic fish showed larger individual variation in swimming activity compared to the controls. The individual variance in activity, tail beat frequency and scattering in the tanks among super oxygenated fish decreased from the 7th to the 21st day of exposure. The behavioural effects of hyperoxia were seen in relation to altered feed consumption halfway through the experiment, lower body weight, and altered haematological variables at day 21 of exposure. Plasma chloride was reduced in the exposed fish and haemoglobin decreased with increasing oxygen saturations. Plasma cortisol was elevated only in the 150% oxygenated group at day 21, while no effect on osmolality was recorded. The alterations in physiology and behaviour from day 7 to day 21 may be explained in terms of acclimation to increased oxygen saturations. This study shows that behaviour may be used as an indication of impaired water quality that may influence animal welfare negatively and eventually prevent an efficient production.