Carbon Dioxide and Oxygen-Nitrogen Ratios as Factors Affecting Salmon Survival in Air-Supersaturated Water

Abstract
Juvenile sockeye salmon (Oncorhynchus nerka) were exposed to lethal levels of air-supersaturated water (120%, 125%, 130% total gas saturation) containing different O2/N2 ratios and different CO2 concentrations. Fish mortality was not significantly different at different CO2 levels (1.7-22.0 mg/l CO2) when tested at the same total gas saturation concentrations. Total gas saturation levels are much more important than the O2/N2 ratios, as fish mortality will not occur unless total gas saturation exceeds 100%, regardless of the O2/N2 ratios. There was a significant decrease in mortality when the O2/N2 ratio was increased while holding the total percent saturation constant. Much more extensive and severe signs of gas bubble disease developed at high O2/N2 ratios than at low O2/N2 ratios, indicating that O2 plays a significant part in forming external emphysema and lesions.

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