Avoidance reactions of rainbow trout to zinc sulphate solutions

Rainbow trout ( Salmo gairdnerii Richardson) showed strong avoidance reactions to sublethal concentrations of zinc sulphate. The threshold avoidance level was 5.6 μg/l of zinc added to laboratory water. This is only 0.01 of the lethal threshold concentration. There were no significant differences in threshold avoidance levels at 9.5° and 17°C., nor when background of zinc in the water was increased during acclimation and/or testing, from 3 μg/l to 13 μg/l.