Factors influencing thiocyanate toxicity in rainbow trout Salmo gairdneri

Tabulated results are presented from experiments on the effects of exercise stress, water hardness, and water chloride concentration on the uptake and toxicity of thiocyanate ion in rainbow trout (Salmo gairdneri). The 96 h LC50 values for thiocyanate in unstressed fish was greater than 94 mg per litre; the mortalities observed in such fish were sporadic and had no apparent relationship with exposure to thiocyanate. A single 30 second bout of strenuous exercise at 96 h induced sudden death in fish exposed to more than 25 mg thiocyanate per litre. Fish were able to accumulate thiocyanate against its diffusion gradient, and the blood concentration in exposed fish exceeded the concentration in the water by up to 5.8 times. However, the blood concentration of thiocyanate fell in fish that survived the exercise bout; possible reasons for this are indicated. The 96 h blood thiocyanate concentration in unstressed fish was inversely related to the chloride content of the water, but was not affected by water hardness.