Toxic effects and molecular mechanisms of Fluopyram on the liver of zebrafish (Danio rerio).

Fluopyram (FLP) is a novel and highly effective succinate dehydrogenase inhibitor (SDHI) fungicide and nematicide. Due to its widespread use in crop disease control, it inevitably enters aquatic environments, where it poses potential threat to aquatic organism safety. However, the ecotoxicological effects of FLP have not been fully elucidated. As a classic aquatic model organism, zebrafish are widely used to investigate the aquatic toxicity of environmental contaminants. In this study, adult zebrafish were exposed to FLP at concentrations of 0.05, 0.1, and 0.5 mg/L for 7, 14, 21, and 28 days to evaluate its effects at the histological, physiological, biochemical, and molecular levels. The results showed that FLP induced oxidative stress, DNA damage, and hepatic injury, inhibited SDH and Complex II activities, and altered the expression of key functional genes associated with mitochondrial respiration, antioxidant, apoptosis, and immunity. Molecular docking revealed that FLP binds to SOD and CAT, thereby disrupting the antioxidant system and exacerbating oxidative stress in zebrafish. Integrated Biomarker Response Index analysis indicated that the highest value (18.87) was observed in the 0.5 mg/L-28 days treatment, suggesting that long-term exposure to high concentrations of FLP poses significant ecological risks. Furthermore, transcriptomic analysis identified numerous differentially expressed genes and enriched signaling pathways, providing mechanistic insight into FLP-induced oxidative stress, mitochondrial and DNA damage, apoptosis, and inflammatory responses. Collectively, these results reveal the toxicity of FLP to adult zebrafish and clarify its potential mechanism of action, which provides an important reference for the ecological risk assessment of FLP in aquatic environments.