The integration of aquaculture with rice culture is an important economic activity in Southern Brazil. However, it generates many problems with regard to land use and water resources. This activity has resulted in the degradation of water quality through the discharge of contaminants from rice crops. The assessment of hematological parameters and antioxidant defenses in fish can be used as biomarkers of water contamination. The aim of this study was to verify the amount of herbicide in the water and evaluate its influence on the hematology and activity of antioxidant enzymes in silver catfish (Rhamdia quelen) from two sites of Madre River, Santa Catarina state, Brazil. Two collection sites were selected: an upstream point and a downstream point of the discharge of water from rice culture. After anesthesia with clove oil the blood samples were collected by caudal puncture, followed by euthanasia and collection of samples from liver to evaluate the activity of the following enzymes: glutathione S-transferase (GST), catalase (CAT), glutathione peroxidase (GPx), glucose 6-phosphate dehydratase (G6PDH), superoxide dismutase (SOD). The water analysis confirmed the presence of clomazone in both sites, more concentrated in downstream point than in upstream point. There was significant increase (p<0.05) in erythrocytes (RBC) and monocytes from downstream point, suggesting xenobiotics stress response. The activity of GST, CAT, GPx and G6PDH was significantly increased (p<0.05) in fish from downstream point, showing a possible condition of oxidative stress caused by contaminants. This study showed the influence of the herbicide contamination on the physiological status of fish from Madre River.
Acknowledgment: This work was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo - Brazil (FAPESP - São Paulo Research Foundation), Grants 2018/24499-8 and CNPq 306635/2018-6.