Chronic toxicity of waterborne thiocyanate to rainbow trout (Oncorhynchus mykiss)

Juvenile rainbow trout (Oncorhynchus mykiss) were exposed to thiocyanate (SCN-) concentrations of 35, 77, 115, or 154 mg . L(-1) for 16 weeks. Mortality occurred either as a chronic mortality throughout the exposure period or as mortality characterized by sudden death syndrome, which occurred immediately after biweekly weighing procedures. The chronic toxicity of SCN- to rainbow trout was characterized by a combined diffuse hyperplastic and diffuse colloid goitre, reduced growth, and decreased hepatosomatic and splenosomatic indices and thyroxine levels compared with pair-fed control fish. Trout also developed an anemia characterized by reduced hematocrit and hemoglobin levels. Plasma SCN- concentrations increased with ambient SCN- levels with bioconcentration factors ranging from 9.3 to 13.4. These observations indicate that chronic SCN- toxicity in rainbow trout is in part due to interference with normal thyroid function.