ORIGINAL ABSTRACT

Glyphosate (GLY), a widely used herbicide, is a significant source of contamination for freshwater ecosystems, potentially impairing the survival, growth, and reproduction of aquatic organisms. Studying its toxicity in freshwater is therefore essential for assessing ecotoxicological risks and identifying relevant bioindicators of pollution.This study aimed to evaluate the effects of GLY on the behavioral, physiological, and metabolic parameters of juvenile Danio rerio whole body under forced and unforced exposure conditions. Fish were exposed to three environmentally relevant concentrations of GLY (C1: 5, C2: 50, and C3:100 µg/L) for 96 h. Avoidance and colonization behaviors were analyzed using the HeMHAS system under unforced exposure, while physiological, biochemical, and behavioral responses (locomotion, anxiety, socialization, aggression, and predation) were assessed under forced exposure. Significant behavioral alterations were observed in the exposed fish, including decreased colonization activity and increased avoidance behaviors. GLY exposure also affected locomotion, resulting in a reduction in absolute turning angle and maximum speed. Social, predatory, and aggressive behaviors were disrupted, particularly at concentrations of 50 and 100 µg/L. Biochemically, alterations in lipid peroxidation and protein oxidation parameters associated with an increase in iron antioxidant capacity were observed, reflecting a concentration-dependent response to oxidative stress. The neurotoxic effect of glyphosate was confirmed by the significant inhibition of acetylcholinesterase (AChE) and carboxylesterase (CaE) activity. Lipidomic analyses revealed a disruption in the fatty acid profile, characterized by a decrease in essential fatty acids (EPA, DHA, and n-3 PUFAs) in favor of pro-inflammatory fatty acids such as arachidonic acid (ARA). However, the ecological interpretation of these results must be considered in light of the current limitations of GLY research. Data regarding its environmental persistence and half-life in aquatic environments remain uncertain and highly variable depending on physicochemical and biological conditions, ranging from a few days to several weeks, which limits the direct extrapolation of experimental results to natural ecosystems. Despite these uncertainties, the results of this study highlight the toxic potential of GLY, even at low concentrations, and confirm the sensitivity of zebrafish as a relevant model for detecting the integrated effects of aquatic contamination by this herbicide.