Survival and iono-regulatory performance in Atlantic salmon smolts is not affected by atrazine exposure

This study was conducted to determine the potential effects of atrazine exposure on survival and physiological performance in Atlantic salmon (Salmo salar) during the period of smoltification. This study involved two separate experiments in which juvenile Atlantic salmon were exposed to atrazine for a four day period in freshwater after which the fish were transferred to 50% seawater for two days and then to 100% seawater for five more days. The nominal concentrations of atrazine tested (1, 10 and 100 microg/L) were representative of and exceeded the levels measured in the North American freshwater environment. After seven days in seawater, fish were weighed, bled for the determination of plasma electrolyte levels, euthanized and samples collected for the determination of gonadosomatic index, muscle water content and gill Na+/K+-ATPase activity. Measured atrazine concentrations during the freshwater exposure period were 76-99% of nominal levels. There were no mortalities attributed to atrazine exposure. There were also no statistically significant differences in body weight, plasma sodium, potassium, magnesium and chloride levels, muscle water content or gill Na+/K+-ATPase activity between control and atrazine treated fish. Measurement of testis and ovary weights showed that there were no treatment effects on relative gonad size in male or female fish. These studies have shown that short term exposure to atrazine during the freshwater phase of their lifecycle had no effects on subsequent survival, body weight, relative gonad size or various measures of iono-regulatory performance in juvenile Atlantic salmon upon transfer to seawater. The concentrations of atrazine tested exceed those likely to be experienced in the natural aquatic environment suggesting that short term exposure to atrazine does not pose a risk to Atlantic salmon during the period of smoltification.