Behavioral assessment of the zebrafish, Danio rerio (Cypriniformes: Cyprinidae), upon chronic exposure to the insecticide Fipronil and its chlorine degradation byproducts

ABSTRACT Despite serious restrictions in most of the world regarding the use of Fipronil in agricultural areas, due to its high toxicity, the insecticide has been used intensively in Brazil, especially since 2022. Used to combat insects that attack crops, Fipronil can be leached from the soil and reach water bodies. Fipronil can also generate even more toxic byproducts when in contact with chlorine dissolved in the water column (chlorine is normally used in public water treatment plants). This study aimed to evaluate the impacts of Fipronil and its chlorine degradation byproducts on the behavior of zebrafish, Danio rerio (Hamilton, 1822). Fishes were exposed to different concentrations of fipronil and its byproducts for 28 and 60 days. Their behavior was recorded using the scan method, with instantaneous recording and a sampling interval of 30 seconds. The results showed that fish exposed to the pesticides in the highest concentrations and for 60 days changed drastically their behavior, becoming more lethargic, swimming more abnormally, and using the bottom of the aquarium more. At low concentrations, the pesticides did not significantly modify the fish’s behavior. Overall, the results showed that fipronil and its byproducts could negatively influence fish behavior, possibly decreasing their fitness and survival and contribute to support studies with wild fish populations.