| Summary: | Hyperoxia has been shown to affect growth, survival and cellular homeostasis in fish. Previous findings onchronic hypoxia (low environmental O2) exposure in Atlantic salmon alevins indicate that re-exposure to normoxicconditions after hypoxia exposure (relative hyperoxia) elevates metabolism above normal. Hence, we hereinvestigated whether acute hyperoxia above normoxic conditions also alters O2) uptake and whether chronichyperoxia affects O2) uptake under normoxic and hypoxic conditions. To this end, the effects of acute and chronichyperoxia exposure on metabolic rate and cardiorespiratory function (heart rate and ventilation rate) in Atlanticsalmon (Salmo salar) alevins incubated at 4 °C were investigated, and how it is affected by an increase in ambienttemperature (4 °C and 8 °C). Hyperoxia (15–18 days at 28 kPa) reared alevins display advanced development compared with normoxiaincubated animals. While acute hypoxia generally leads to metabolic depression (≈70%, 21 kPa compared with5 kPa), acute hyperoxia (28 kPa) causes hypermetabolism (≈30% compared with normoxia at 4 °C and ≈20% at8 °C). Chronic hyperoxic rearing on the other hand did not alter metabolic rate at 4 °C or 8 °C in acute hyperoxia,normoxia or hypoxia. Heart rates and ventilation rates were also unaltered with acute hyperoxia and wereunaffected by chronic hyperoxia exposure. It is shown that acute hyperoxia increases O2) uptake above normoxicconditions but chronic hyperoxia does not result in long term physiological changes. This adds further proof thatO2) uptake is not limited by O2) transport capacity but by O2) availability at this developmental stage in salmonids.
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