Diflubenzuron persists and impairs behavioral and biochemical responses in the giant freshwater prawn (Macrobrachium rosenbergii)

The intensive use of insecticides such as diflubenzuron (DFB), although effective for controlling ectoparasites in aquaculture, raises concerns regarding its environmental persistence and sublethal effects on non-target organisms. This study investigated the bioaccumulation, depletion, and sublethal effects of DFB in the freshwater prawn Macrobrachium rosenbergii , integrating kinetic, biochemical, and behavioral responses. Juveniles were exposed for seven days to two environmentally relevant concentrations of radiolabeled 14 C-DFB (0.5 and 5 μg L −1 ), followed by seven days in clean water to evaluate depletion. Body radioactivity was monitored daily, and antioxidant defense (catalase - CAT, reduced glutathione - GSH, and glutathione reductase - GR), biotransformation (glutathione S-transferase - GST), neurotoxicity (acetylcholinesterase - AChE), and oxidative damage biomarkers (malondialdehyde - MDA) were measured at the end of each phase. Escape velocity and behavioral alterations were also assessed. Results indicated rapid bioaccumulation of DFB-derived residues and slow, incomplete elimination, with estimated biological half-life values of 72.0 and 79.3 days at 0.5 and 5 μg L −1 , respectively. Mass balance (MB) analysis showed that most radioactivity remained in the water, while 22.25% and 13.30% were retained in shrimp at the lower and higher concentrations tested, respectively. Biochemical responses included increased GR activity in both treatments, increased GST activity mainly at the lower concentration, and elevated lipid peroxidation, whereas CAT and total GSH were not significantly altered. AChE activity increased during exposure and returned to control levels during depletion. Behavioral analysis showed a significant reduction in escape velocity after seven days of exposure; at day 14, this impairment persisted only at the higher concentration, while the lower-concentration treatment showed partial recovery. Abnormal behaviors, such as lethargy, erratic swimming, and early cannibalism were also observed. Overall, the results suggest that environmentally relevant concentrations of DFB can impair key physiological and behavioral functions in M. rosenbergii , with some effects persisting even after exposure cessation.