Susceptibility of steelhead trout Salmo gairdneri Richardson to redmouth infection Yersinia ruckeri following exposure to copper

Steelhead trout were exposed to sublethal concentrations of copper and inoculated with Yersinia ruckeri. Copper exposure at 7 and 10 μg/1 for 96 h caused more fish to die of infection than control fish (no copper). Infection susceptibility increased with time of exposure to a single dosage of copper (10 μg/1), reaching a maximum at 48 h. Lowering the copper concentration to 5 μg/1 caused the infection susceptibility to occur at 24 h. The infectious dose of Y. ruckeri was lower in fish exposed to 10 μg/1 copper for 48 h than control fish.