Sub-Lethal Peak Exposure to Insecticides Triggers Olfaction-Mediated Avoidance in Zebrafish Larvae

In agricultural areas, insecticides
inevitably reach water bodies
via leaching or run-off. While designed to be neurotoxic to insects,
insecticides have adverse effects on a multitude of organisms due
to the high conservation of the nervous system among phyla. To estimate
the ecological effects of insecticides, it is important to investigate
their impact on non-target organisms such as fish. Using zebrafish
as the model, we investigated how different classes of insecticides
influence fish behavior and uncovered neuronal underpinnings of the
associated behavioral changes, providing an unprecedented insight
into the perception of these chemicals by fish. We observed that zebrafish
larvae avoid diazinon and imidacloprid while showing no response to
other insecticides with the same mode of action. Moreover, ablation
of olfaction abolished the aversive responses, indicating that fish
smelled the insecticides. Assessment of neuronal activity in 289 brain
regions showed that hypothalamic areas involved in stress response
were among the regions with the largest changes, indicating that the
observed behavioral response resembles reactions to stimuli that threaten
homeostasis, such as changes in water chemistry. Our results contribute
to the understanding of the environmental impact of insecticide exposure
and can help refine acute toxicity assessment.