Chronic cyanide poisoning of rainbow trout and its effects on growth, respiration, and liver histopathology.

Cyanide markedly affected growth and resting metabolic rate while causing degenerative hepatic necrosis in juvenile rainbow trout (Salmo gairdneri, Richardson). This was revealed during two experiments performed in continuously renewed water at 12.5 degree C with fish fed a restricted artificial diet and exposed to assayed cyanide concentrations of 0.00, 0.01, 0.02, or 0.03 mg/L hydrogen cyanide (HCN) for 18 days. At 0.02 and 0.03 mg/L, HCN growth was reduced by 40 to 95% after 18 days. At all concentrations, cyanide caused a severe initial repression of specific growth rate, followed by a highly significant increase which was insufficient to compensate for the original repression. Previous exposure to cyanide promoted a higher resting metabolic rate during the six days following exposure, the effect increasing with cyanide concentration. At all concentrations tested, widespread cyanide-induced degenerative necrosis of hepatocytes was observed; it was more intense at higher cyanide concentrations and well established even at 0.01 mg/L HCN.