Hematological and biochemical alterations in the fish Prochilodus lineatus caused by the herbicide clomazone

• Clomazone increased red blood cells count, possibly as an adaptive response.
• Clomazone increased liver activity of the biotransformation enzyme GST.
• Brain acetylcholinesterase activity was inhibited after clomazone exposure.

The indiscriminate use of herbicides has led to the contamination of water bodies, possibly affecting the health of aquatic biota. Therefore, to evaluate the possible effects of the clomazone-based herbicide (Gamit® 500) on the fish Prochilodus lineatus, juveniles were exposed for 96 h to three concentrations (1, 5 and 10 mg L−1) of clomazone, and an analysis was made of their hematological parameters: hemoglobin (Hb); hematocrit (Hct); red blood cell (RBC) count; mean corpuscular volume (MCV); mean corpuscular hemoglobin (MCH); mean corpuscular hemoglobin concentration (MCHC) and biochemical parameters: glutathione S-transferase (GST); catalase (CAT); glutathione peroxidase (GPx) and acetylcholinesterase (AChE). Hct presented a significant decrease at the concentration of 10 mg L−1, while the parameters Hb, HCM and MCHC presented a significant decrease at the two higher concentrations, indicating an anemic condition. The RBC increased significantly at the lowest concentration, possibly due to the release of new red blood cells into the bloodstream in response to splenic contraction, which may occur as an adaptive response to the stressor agent. P. lineatus presented activation of the biotransformation pathway, indicated by augmented hepatic activity of the enzyme GST and hepatic activation of the antioxidant enzyme CAT at the higher concentrations. Liver GPx was significantly inhibited at the higher concentrations, which may indicate the efficient action of CAT in the elimination of H2O2 or its competition with GST for the same substrate (GSH). AChE activity in brain and muscle was inhibited at the higher concentrations, indicating the neurotoxic effects of the herbicide in the fish. The hematological and biochemical alterations led to the conclusion that the herbicide clomazone has toxic effects on the species P. lineatus, and that its presence in the environment may jeopardize the health of these animals.