Physiological effects of normbaric environmental hyperoxia on Atlantic salmon (Salmo salar L.) presmolts

In order to investigate the dose–response relationship of normbaric hyperoxia, Atlantic salmon (Salmo salar) presmolts were reared in freshwater and exposed for 37 days to four levels of environmental hyperoxia relevant in an intensive fish hatchery situation. The four oxygen saturation levels were: 93% (Control), 125%, 145% and 178%, measured in effluent water.Breathing frequency and hematocrit levels decreased with increasing level of hyperoxia, while levels of blood PCO2 and HCO3− increased. There was a significant dose–response relationship between the level of water oxygen saturation and the blood PCO2 level, as was the case for the HCO3− level. These dose-dependent responses indicate haematological and physiological adaptations to the increasing levels of environmental hyperoxia. However, these adaptations did not seem to cause any serious physiological perturbation to the fish as no negative effects on growth or mortality were observed in the present trial.