The effects of cyanide on iono- and osmoregulation are soon established and last long after the period of exposure to the toxicant is over. The effects are of the order of 4 to 8 percent changes in blood plasma osmolality and chloride ions, changes which are indicative of serious physiological impairment, having costly energetic implications. The deleterious effects of cyanide were detected at concentrations as low as 0.01 mg/l HCN in water of pH 7.5.

Juvenile rainbow trout, Salmo gairdneri, were first exposed to various concentrations of cyanide ranging from 0.01 to 0.037 mg/1 HCN for 28 days in fresh water in flow-through aquaria at 10?C. After this exposure period the fish together with untreated fresh water controls were transferred into 18.9 ppt salt water for 260 hours during which blood plasma osmolality and chloride were monitored. By the end of the salinity tolerance tests the poisoned fish had experienced greater loss of water than the controls but no change of chloride were observed. Upon return to fresh water for 100 hours all the fish lost chloride ions, the effect being much greater in the cyanide exposed fish. When the fish were first adapted to salt water then transferred to fresh water cyanide they also experienced loss of chloride and dilution of plasma greater than the controls did.

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