Effect of sodium chloride on physiological parameters of juvenile Brycon amazonicus (matrinxã)

The use of common salt or sodium chloride (NaCl) has been recommended to reduce stress caused in freshwater fish due to fish farming management. The argument is that NaCl tends to decrease the osmotic gradient between the water and the animal, reallocating energy for growth and reproduction and reestablishing homeostasis. However, it is necessary to understand the effect of salt concentrations on the physiology and welfare of freshwater fish. Thus, the aim of this study was to evaluate the physiological parameters at different concentrations of NaCl in water used for rearing juvenile Brycon amazonicus (matrinxã). Five experimental treatments were performed: 0, 6, 10, 14 and 15 g/L of NaCl. The fish weighed 678.28 ± 53.15 g, measured 29.91 ± 1.13 cm in length and were maintained in tanks for 96 h. In the first 6 h, only fish in the 15 g/L concentration died. At the end of the 96 h of exposure to different concentrations of NaCl, blood was collected to analyze the blood parameters of the rest of the animals. The 14 g/L of NaCl treatment showed lower values of hemoglobin, hematocrit and total protein, and higher values of plasma triglycerides, sodium, potassium, chloride and cortisol ions, suggesting a reduction in oxygen transport, plasma electrolyte imbalance and physiological stress. Although no apparent signs of physiological stress were observed, in the treatment using 10 g/L of NaCl, the fish also showed low oxygen transport capacity, hypercholesterolemia and electrolyte disturbances. Therefore, this study indicates that 6 g/L of NaCl may be used for juvenile matrinxã for 96 h, as it does not alter the hematological parameters investigated.