Dietary Exposure to Bifenthrin and Fipronil Impacts SwimmingPerformance in Juvenile Chinook Salmon (Oncorhynchustshawytscha)

:two commonly used insecticides, bifenthrin andfipronil,can accumulate in the prey of juvenile Chinook salmon, yet the effects ofdietary exposure are not understood. Therefore, to better characterize theeffect of a dietary exposure route, juvenile Chinook salmon were fedchironomids dosed with a concentration of 9 or 900 ng/g of bifenthrin,fipronil, or their mixture for 25 days at concentrations previouslymeasured infield-collected samples. Chinook were assessed for maximumswimming performance (Umax) using a short-duration constant accel-eration test and biochemical responses related to energetic processes(glucose levels) and liver health (aspartate aminotransferase (AST)activity). Chinook exposed to bifenthrin and bifenthrin andfipronilmixtures had a significantly reduced swimming performance, although notwhen exposed tofipronil alone. The AST activity was significantlyincreased in bifenthrin and mixture treatments and glucose levels were increased in Chinook following a mixture treatment, althoughnot when exposed tofipronil alone. Thesefindings suggest that there are different metabolic processes between bifenthrin andfipronil following dietary uptake that may influence toxicity. The significant reductions in swimming performance and increasedlevels of biochemical processes involved in energetics andfish heath could have implications for foraging activity and predatoravoidance in wildfish at sensitive life stages.

Automated summary

This study found that dietary exposure to bifenthrin and bifenthrin and fipronil mixture significantly reduced the swimming performance of juvenile Chinook salmon. The activity of AST was significantly increased in the bifenthrin and mixture treatments, while the glucose levels were increased in the mixture treatment. These findings suggest that there are different metabolic processes between bifenthrin and fipronil following dietary uptake that may influence toxicity. Reduced swimming performance and increased biochemical processes could have implications for foraging activity and predator avoidance in sensitive life stages of wild fish.