The impact of a pesticide on migratory activity and olfactory function in Atlantic salmon (Salmo salar L.) smolts

The S-triazine pesticide atrazine (2-chloro-4-ethylamino-6-isopropylamino-S-triazine), which is known to modify the parr–smolt transformation and olfactory function in adult Atlantic salmon had a significant effect on migratory activity and the olfactory sensitivity of salmon smolts. Exposure of smolts for 81 days to 5.0 μg l− 1 atrazine during the parr–smolt transformation significantly reduced migratory activity in an experimental stream tank during the period of peak migration in the wild population. Exposure of smolts to the 0.5 μg l− 1 atrazine in freshwater resulted in a significant decrease in the gill Na+K+ ATPase activity but not at the higher 5.0 μg l− 1 concentration. Further, there were no significant effects on plasma thyroid hormone (T3 or T4) levels. On transfer to saltwater there was no significant effect on gill Na+K+ ATPase activity or T3 or T4 concentrations when compared to the relevant freshwater groups. After exposure to atrazine at nominal concentration of 0.5, 1.0, 2.0 and 5.0 μg l− 1 electrophysiological responses recorded from the olfactory epithelium of salmon smolts to both l-serine and smolt urine were significantly reduced. Although at the highest nominal concentration tested (5.0 μg l− 1), responses were still recorded from the epithelium, the amplitudes were only 43 ± 8.8% (urine) and 33 ± 9.6% (l-serine) compared to the control. The results of the study are discussed in relation to the possible sublethal impacts of atrazine on the biology of salmon with particular emphasis on migration, imprinting and homing.