Toxic Effects of Povidone-Iodine on Macrobrachium rosenbergii: Concentration-Dependent Responses in Oxidative Stress, Immunosuppression, and Recovery Potential

Abstract

Povidone-iodine (PVP-I), a widely used aquaculture disinfectant, remains poorly understood in terms of sublethal toxicity and damage reversibility. This study employed Macrobrachium rosenbergii as the model organism to evaluate the acute toxicity and sublethal effects of PVP-I through a 4-day exposure experiment followed by a 7-day depuration period. Acute toxicity tests enabled the determination of 24–96 h median lethal concentrations (LC50), with the 96 h LC50 being 5.67 mg/L and the safe concentration (SC) being 1.37 mg/L. Based on this, three sublethal concentrations (1.14, 1.89, and 2.84 mg/L) were tested over a 4-day exposure followed by a 7-day depuration period. Investigated endpoints included gill ultrastructure, apoptosis, and antioxidant and immune-related gene expression. Subacute exposure at 1.89 and 2.84 mg/L induced mitochondrial vacuolization, upregulated apoptosis-related genes (Cyt-c, Caspase-3, Bok), and downregulated antioxidant gene expression (SOD, CAT, GSH-Px). The high-concentration group also showed sustained Toll-like receptor (Toll) gene overexpression and acid phosphatase (ACP) gene suppression. After depuration, antioxidant gene expression normalized; however, apoptotic markers in gill tissue remained impaired. Overall, high PVP-I concentrations cause irreversible gill damage via mitochondrial-mediated apoptosis, whereas lower concentrations (≤1.14 mg/L) allow for greater recovery. These results offer crucial toxicodynamic insights for safer PVP-I use and risk assessment in M. rosenbergii aquaculture.