Biochemical Effects of Didecyldimethylammonium Chloride (DDAC) Exposure and Osmoregulatory Stress on Juvenile Coho Salmon, Oncorhynchus kisutch

Abstract.

The effects of a seawater challenge on coho salmon, Oncorhynchus kisutch, previously exposed to didecyldimethylammonium chloride (DDAC) were examined. In one experiment, salmon were exposed to three sublethal concentrations of DDAC over three durations followed by a 24-h seawater challenge in a computer-controlled, intermittent-flow respirometer to measure effects on several biochemical variables. After a 144-h dose, plasma cortisol, glucose, and gill Na⁺/K⁺-ATPase activity were significantly increased at a nominal DDAC concentration of 0.2 mg/L. In the second experiment, animals were exposed to five different concentrations for 24 h followed by a 24-h seawater challenge. Plasma cortisol was significantly increased at the highest exposure concentration (0.75 mg/L). Plasma Na⁺ was significantly elevated at exposure concentrations of 0.3, 0.5, 0.65, and 0.75 mg/L. Gill Na⁺/K⁺-ATPase activity was significantly reduced at exposure concentrations of 0.65 mg/L and 0.75 mg/L. The use of the seawater challenge to demonstrate sublethal physiological stress and impaired osmoregulatory capacity in coho salmon smolts is relevant to salmonid life history in terms of the animal's transition from freshwater to seawater during its seaward migration.