THE SILENT GRIM REAPER: ACUTE EXPOSURE TO 3,4-DCA RESULTS IN ELEVATED MORTALITY IN ANNUAL FISH Nothobranchius furzeri EMBRYOS EVEN AFTER THE EXPOSURE PERIOD

Resumo

INTRODUCTION: The environmental contaminant 3,4-dichloroaniline (3,4-DCA) is used as an intermediate in the synthesis of Diuron, a widely applied herbicide in Brazilian sugarcane crops. Nothobranchius furzeri is an annual killifish known for its desiccation-resistant embryos and has recently emerged as a valuable model for evaluating toxicological effects on non-target organisms. Investigating its responses to contaminants can provide important insights into how endangered annual killifish species may be affected by similar environmental threats. OBJECTIVE: This study aimed to assess the effects of aquatic exposure to different concentrations of 3,4-DCA on the survival of N. furzeri embryos and whether the effects persist after embryos undergo a desiccation period, a typical phase in the life cycle of annual killifishes. MATERIALS AND METHODS: Embryos were individually placed in 24-well plates (2 mL per well) and exposed to 1, 2, 4, and 8 mg/L concentrations of 3,4-DCA, alongside a control group. Exposures were conducted in a semi-static system with complete medium renewal every 96 hours, over 8 days, using reconstituted water. During exposure, embryos were maintained at 27°C under a 12h:12h light-dark photoperiod. After exposure, embryos were transferred to a dry substrate for 14 days to complete development. Survival was monitored daily under a stereomicroscope. RESULTS AND CONCLUSION: Survival analysis indicated that the exposed groups exhibited higher mortality rates compared to the control group (1 mg/L: 9-fold increase; 2 mg/L: 6-fold increase; 4 mg/L: 9-fold increase; 8 mg/L: 5.5-fold increase; p < 0.01). Specifically, embryos exposed to 8 mg/L showed higher mortality during the exposure period compared to the other groups. During the post-exposure period, embryos exposed to 1, 2, and 4 mg/L exhibited a significant increase in mortality rates compared to the 8 mg/L group, which maintained stable survival (p < 0.01), suggesting that damage caused during the exposure phase impairs essential protective mechanisms, making the embryos more susceptible to desiccation. In conclusion, exposure to 3,4-DCA may impair physiological resilience processes in N. furzeri embryos, compromising their survival in fluctuating environments.