Temperature and oxygen-nitrogen gas ratios affect fish survival in air-supersaturated water

Abstract

Juvenile steelhead trout and juvenile chinook, coho and sockeye salmon were tested at different temperatures (8°, 9°, 10°, 12°, 15°, 18° and 20°C) at the same concentration of air-supersaturated water. Supersaturated water concentrations in different tests were 115, 116, 117, 118 and 120% saturation. Increased temperatures caused a significant ( P< 0.005) increase in steelhead mortality, a significant increase ( P < 0.025) in chinook deaths, but no significant effect on coho or sockeye mortality. Regression model data for steelhead indicate that a 10°C increase in temperature will decrease the time to 50% death by a factor of 2.7, e.g. from 190h at 8°C to 70h at 18°C, when tested at the same total dissolved gas pressure. Effects of different oxygen-nitrogen gas ratios on fish mortality at the same total dissolved gas pressure in supersaturated water were demonstrated with juvenile steelhead trout. Mortality was rapid (time to 50% death in 1–6 h) at 140, 135 and 130% saturation, with fish dying more rapidly as the ratio of oxygen-nitrogen decreased (decrease in O 2, increase in N 2) Mortality patterns were similar at 125%; time to 50% death occurred in 5–20 h, with more rapid deaths occurring as oxygen (O 2/N 2 ratio) was decreased.