Acute toxicity and sublethal effects of Paraquat in Colossoma macropomum : toxicological responses and recovery based on hematological, genotoxic, and histopathological biomarkers

The herbicide Paraquat, widely used in agriculture, poses a significant risk to aquatic organisms due to its high toxicity. This study investigated the acute toxic effects and recovery process in tambaqui (Colossoma macropomum), a key species in the Amazon Basin, using hematological, genotoxic, histopathological, and biochemical analyses. Initially, fish were exposed to different Paraquat concentrations (0, 10, 15, 20, 25, 30, and 35 mg/L) to determine the median lethal concentration (LC50-96 h), estimated at 26.66 mg/L. Subsequently, a sublethal exposure (96 h) to concentrations of 0, 10, and 15 mg/L was conducted, followed by a recovery period in clean water for 7 and 15 days. The results revealed significant hematological alterations, including changes in hematological indices and leukocyte counts, indicating immune system impairment. Genotoxicity was confirmed by increased micronuclei and nuclear abnormalities in erythrocytes, suggesting potential mutagenic effects. Histopathological analysis showed severe damage in the gills, liver, and kidneys, including hyperplasia, hepatic vacuolisation, and renal degeneration, with some alterations persisting even after 15 days of recovery. Additionally, depletion of muscle and hepatic glycogen was observed, reflecting prolonged metabolic disturbances. In conclusion, Paraquat causes significant harm to C. macropomum, with long-lasting effects that may compromise its survival and ecological role.