Immediate avoidance behavior and short-term toxic effects of the antidepressants citalopram and sertraline in zebrafish: Habitat selection, behavioral and biochemical disruptions.

Antidepressants are among the most widely prescribed pharmaceuticals worldwide, and compounds such as sertraline and citalopram have been detected in surface waters, raising concerns about their impacts on non-target aquatic organisms. The current study aimed to (i) evaluate immediate behavioral responses to citalopram and sertraline using habitat selection (avoidance and colonization) in zebrafish (Danio rerio) under non-forced exposure, and (ii) integrate these responses with short-term biochemical and behavioral alterations after forced exposure. Concentrations tested were 0.05, 0.2, 1, and 15 µg/L for citalopram and 0.05, 0.1, 0.5, and 2 µg/L for sertraline. In non-forced exposure, fish underwent individual avoidance/colonization tests (5 min) and a population avoidance test (3 h); In forced exposure, fish were exposed for 48 h to each concentration to assess behavioral and biochemical biomarkers. Under non-forced exposure, the zebrafish population avoided all tested concentrations, preferring the least contaminated compartments (p < 0.05). Forced exposure induced predatory inhibition (citalopram: 0.05 and 1 µg/L; sertraline: 0.5-2 µg/L; p < 0.05), hypolocomotion (citalopram: 0.2-1 µg/L; sertraline: 0.5 µg/L; p < 0.05), and anxiety-like responses (citalopram: 15 µg/L; sertraline: 2 µg/L; p < 0.05); only sertraline increased aggressive behavior (0.1-2 µg/L, p < 0.01). Both antidepressants significantly increased antioxidant defenses, with Glutathione S-transferase and Catalase the most sensitive biomarkers, responding from 0.05 µg/L (citalopram) and 0.1 µg/L (sertraline), depending on tissue (p < 0.05). Acetylcholinesterase activity was altered at similar concentrations (p < 0.05). Integrating non-forced habitat selection with forced-exposure biomarkers revealed both contaminant avoidance and latent toxicity not be captured by conventional single-compartment assays.