Two
commonly used insecticides, bifenthrin and fipronil, can accumulate
in the prey of juvenile Chinook salmon, yet the effects of dietary
exposure are not understood. Therefore, to better characterize the
effect of a dietary exposure route, juvenile Chinook salmon were fed
chironomids dosed with a concentration of 9 or 900 ng/g of bifenthrin,
fipronil, or their mixture for 25 days at concentrations previously
measured in field-collected samples. Chinook were assessed for maximum
swimming performance (U
max) using a short-duration
constant acceleration test and biochemical responses related to energetic
processes (glucose levels) and liver health (aspartate aminotransferase
(AST) activity). Chinook exposed to bifenthrin and bifenthrin and
fipronil mixtures had a significantly reduced swimming performance,
although not when exposed to fipronil alone. The AST activity was
significantly increased in bifenthrin and mixture treatments and glucose
levels were increased in Chinook following a mixture treatment, although
not when exposed to fipronil alone. These findings suggest that there
are different metabolic processes between bifenthrin and fipronil
following dietary uptake that may influence toxicity. The significant
reductions in swimming performance and increased levels of biochemical
processes involved in energetics and fish heath could have implications
for foraging activity and predator avoidance in wild fish at sensitive
life stages.