A preliminary study of the effect of physical activity on the resistance of rainbow trout (Salmo gairdnerii Richardson) to two poisons

SUMMARY The toxicity of zinc sulphate and ammonium chloride to rainbow trout forced to swim continuously against water currents of three known velocities has been compared with their toxicity to similar fish tested simultaneously in still water. For fish swimming at 85% of the maximum sustainable velocity the concentration of ammonium chloride killing 50% at 24 hr. was 0·81 times that for still water, and the corresponding factor for 48 hr. exposure to zinc sulphate was 0·70. Current speeds up to 55% of the maximum sustainable velocity produced no detectable increase in susceptibility to either poison. The increase in metabolic rate with current velocity was measured, and its relation to the increase in susceptibility to poisons is discussed.