Ventilation and metabolic rate of young rainbow trout (Salmo gairdneri) exposed to sublethal environmental pH

Differences between ventilatory response and metabolic rates of young rainbow trout tested within the sublethal range of pH 6 to pH 9 were observed using a flowing water respirometer. The oxygen consumption was monitored at swimming speeds of 12 cm/sec and 24 cm/sec. The oxygen consumption rates at 24 cm/sec and pH 6 (423 mg/kg-hr) and pH 9 (367 mg/kg-hr) were considerably higher than those determined near neutrality (328 mg/kg-hr). Ventilation rate increased to either side of neutrality, but significantly fewer respiratory reversals, or "coughs," were observed at pH 6 and a greater number at pH 9 than occurred at pH 7 and 8 or in untested fish. The respiratory-cough response is shown to be pH-dependent in rainbow trout and may therefore not be as reliable an indication of pollutant-caused stress in studies where the experimental pH has not been specified or controlled.