Investigation effect of salt supplementation on change of gill and kidney tissues of Rutilus kutum

In this research, it was used salt supplement in feed of Rutilus kutum juveniles (about one gram) in the freshwater environment by aim of changes of gill and kidney tissue for stimulating osmotic regulation system. The purpose of this research, was to improve survival rate of juveniles’ fish during move time to brackish water. It was initial average weight for Juveniles’ fish 0.91±0.01 g (mean±SE). Experiments carried out in two phases. In step one, the fish were put for 15 days in freshwater and they were fed with commercial diet containing NaCl supplement in four treatments (control without NaCl supplement, 5, 7 and 10 percent). The each treatment had three replications. In the second step, the fish were moved to brackish water of Caspian Sea (12.5 psu) and they were fed for 28 days with a commercial diet (without NaCl supplement). The results in step one showed that it was not changed renal tissue in all treatments. But, it was observed significant difference between size of glomerulus and renal tubules between freshwater and brackish water environments (between step one and two), (P<0.05). In steps one, there were observed gill accessory cells in all treatments that fed salt supplements. At the end of the second step, number of gill chloride cells in control treatment was lower than other treatments that it fed in ones step with salt supplementation (P<0.05). The results showed that it was survival rate in fish fed dietary supplements of sodium chloride 5% more than other treatments (P<0.05). Therefore, feed low level salt supplement in diet of Rutilus Kutum fingerlings in freshwater is fish physiologic provocation against environmental saline water.