Seasonal changes in certain metabolic and haematologic responses of Salmo gairdneri acutely exposed to dehydroabietic acid (DHAA).

Physiological effects of a high sublethal DHAA exposure on respiration, ammonia excretion and haematology of rainbow trout were studied in July at 15 degrees C and in December at 10 degrees C. In the control fish plasma glucose concentration was higher (P less than 0.001) in December than in July, but plasma protein (P less than 0.02) and Na+ (P less than 0.001) concentrations were lower. Due to DHAA exposure the oxygen consumption (P less than 0.01) and ammonia excretion rates (P less than 0.001) increased significantly in July but not in December. In December a significant decrease in plasma Cl- and increase in plasma protein concentration occurred with a slight haemoconcentration. Microscopic examination of the gills, performed on the trout in December only, revealed a 25% hypertrophy of secondary lamellar structures due to the exposure.