Effect of nitrate on hematological and oxidative stress parameters of juvenile mullet (Mugil liza) in fresh water
This study aimed to evaluate the sublethal effects of the exposure of juvenile mullet (Mugil liza) to nitrate in fresh water. Therefore, the median lethal concentration (LC50-96h) to nitrate (0; 86; 462; 852 and 968 mg N-NO3 L-1) was determined, which was estimated at 606.07 mg N-NO3 L -1. After defining the LC50-96h, the fish (105.2 ± 8.4 g) were exposed, for 5 days, to three sublethal concentrations of nitrate (8.0 ± 2.0; 34.0 ± 1.0; 52 , 0 ± 6.0 mg N-NO3 L-1) and a control (0.05 ± 0.02 mg NNO3 L-1). During this period, blood samples were taken to determine glucose, hematocrit, hemoglobin, erythrocyte count, blood pH and hematimetric indices (1 and 5 days) after fish exposure to nitrate. For the oxidative stress analyzes, gills, liver and muscle collections were performed (1, 2 and 5 days),after exposure to experimental conditions. Nine fish / collection / treatment were collected to check the levels of lipoperoxidation (LPO-TBARS), total antioxidant capacity against peroxyl radicals (ACAP) and the activity of glutathione S-transferase (GST). The glucose concentrations in the plasma of M. liza initially showed a decrease (1 day) and an increase (5 days) in the highest concentrations of nitrate (34 and 52 mg N-NO3 L-1) compared to the control and 8 mg N -NO3 L-1. The erythrocyte levels decreased in the highest concentration (52 mg N-NO3 L-1 - 1 day) when compared to the other treatments. Hemoglobin, after 5 days of exposure to nitrate, increased significantly in all treatments when compared to day 1. The hematimetric indices (CMV,HCM and CHCM) showed changes in different treatments over time and between treatments. Exposure to nitrate increased the OLP (1 day) in the gills of animals exposed to 34 mg NO3-N L-1 compared to the control. The ACAP in the gills and liver of mullet juveniles were higher in animals exposed to higher concentrations of nitrate (34 and 52 mg N-NO3 L-1), in contrast the muscle had a lower antioxidant capacity. GST activity in the gills, liver and muscle of M. liza, in our study, showed a reduction during the experimental period (5 days). Thus, we conclude that exposure to nitrate alters the biochemical parameters of juvenile mullet (Mugil liza) in fresh water, causing changes in lipoperoxidation, antioxidant capacity and GST activity in fish.