The Effect of Sodium Chloride Supplementation in the Diet of Juvenile Wild Common Carp on Survival, Antioxidant and Ionic Characteristics, and Tissue Histology under Sudden Salinity Stress

This study aimed to investigate the effect of salt (sodium chloride) supplementation in the diet on survival, biochemical indices, and tissue histology of juvenile wild common carp under salinity stress. Fish fry (approximately 1.1 g) were fed diets containing 0%, 5%, and 10% sodium chloride for 15 days, then directly transferred to brackish water (13 g/L) and sampled after 3 and 10 days. Diet or sampling time had no significant effect on survival and body moisture of fish. Sodium, glutathione reductase, and glutathione peroxidase levels in the body significantly increased three days after salinity stress, and returned to pre-stress levels after 10 days. Body moisture levels significantly decreased after salinity stress, but potassium and chloride levels in the body increased and remained significantly higher than pre-stress levels for up to 10 days. Prior to salinity stress, glutathione levels were higher in high salt treatment groups compared to control groups, and 10 days after salt stress, glutathione levels were higher in the 10% salt treatment group compared to the other two groups. Malondialdehyde in the body was significantly lower in sodium chloride treatments than the control. No significant and important histological lesions were found in the fish gill and kidney after salinity stress. This study suggests that wild carp fry can tolerate direct transfer to the Caspian Sea brackish water, without dietary sodium chloride supplementation. Dietary 10 g/kg salt supplementation decreases lipid peroxidation in the fish.