Different levels of hardness and ammonia in the water and their implications for the oxidative stress parameters of jundiá (Rhamdia quelen Quoy & Gaimard, 1824)
In the present study, the effects of different levels of hardness (25 and 120 mg CaCO3 L-1) and non-ionized ammonia (0.02; 0.18 and 0.50 mg NH3 L − 1) on water on parameters of oxidative stress in juveniles of jundiá Rhamdia quelen for a period of five days. Liver and gills were collected from the animals, before exposure to ammonia, 1 and 5 days after exposure for analysis of lipoperoxidation (TBARS), glutathione transferase (GST) and catalase (CAT). No influence of hardness levels on mortality was observed, however treatments with 0.50 mg NH3 L-1, in both hardness levels, reached 100% mortality after 24 h. TBARS levels in the liver were significantly higher (89.8%) in the treatment with 25 mg CaCO3 L-1 - 0.18 mg NH3 L-1 compared to the treatment 120 mg CaCO3 L-1 - 0.18 mg NH3 L-1 on the 5th day exposure. In the gills,the treatment 25 mg CaCO3 L-1 - 0.18 mg NH3 L-1 showed a 132.6% increase in TBARS levels on the fifth day when compared to the control. The 120 mg CaCO3 L-1 treatments - 0.02 and 0.18 mg NH3 L-1 showed a decrease of 145.1 and 122.7%, respectively, in TBARS levels in relation to the control. On the fifth day of exposure, treatments with 25 mg CaCO3 L-1, in both ammonia levels, showed higher levels of TBARS compared to treatments with 120 mg CaCO3 L-1 in both ammonia levels. The CAT enzyme in the liver showed a decrease (65.5%) and an increase (172.9%) of its activity, on the fifth day, in the treatments 25 mg CaCO3 L-1 - 0.02 and 0.18 mg NH3 L-1, respectively when compared to the control. In gills, CAT showed greater activity in the treatment 25 mg CaCO3 L-1 - 0.18 mg NH3 L-1 when compared to the other treatments (73.1; 104.5 and 150.3%). On the fifth day, the enzyme GST showed a decrease in activity of around 45%, in the liver of animals exposed to 120 mg CaCO3 L-1 - 0.18 mg NH3 L-1 when compared to the other treatments. The results demonstrate that high levels of hardness are not able to prevent mortality in animals exposed to extreme concentrations of non-ionized ammonia, however it has a beneficial effect in improving the oxidative status of the animals.