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Rainbow trout 23 to 30cm in fork length were exposed to various concentrations (1 to 40ppm) of a cationic, quaternary ammonium compound, Zephiran. Three ppm was used as a reference value, as this level is recommended at the water hardness found in Southern Ontario (Canada). Gills were examined using light microscopy, scanning and transn~ission electron microscopy. Changes were observed in gills from fish exposed to all concentrations of Zephiran, becoming more severe as the concentration and/or number of exposures increased. Gills were severely spongiot~c and necrotic, and there was much lamellar fusion through apposition. Membrane vesiculation, hydropic degeneration, and exfoliation of lamellar and interlamellar epithelium were also present. Blood chemistry was examined following the second exposure of fish to 3 ppm Zephiran. Haematocrit, serum protein and serum albumin concentrations increased significantly, whereas sodium, chloride and magnesium concentrations decreased; phosphorus, calcium and potassium levels did not change significantly. It is suggested that fish became hypoxic as a result of damage to the gills and that this resulted in a respiratory acidosis causing loss of serum water to the hyperosmotic extravascular tissues. Sodium and chloride were probably lost to the surrounding water via diffusion through the damaged lamellar epithelium. The dramatic drop in sodium and chloride concentration corroborates the severity of lesions seen histologically and ultrastructurally following exposure to Zephiran. In conclusion, the use of Zephiran in the treatment of fish bacterial d~seases (e.g. bacterial gill disease) is not recommended in light of the severe changes which follow exposure to therapeutic concentrations.

Effects of a cationic detergent on the gills and blood chemistry of rainbow trout Salmo gairdneri