Stimulation of osmoregulation system and comparison growth performance of Rutilus Kutum (less than a gram) with using salty diet at freshwater

Abstract

In this research was used sodium chloride in feed supplement to stimulate ion- osmotic regulation system of Rutilus Kutum juveniles (about one gram) in fresh water environment.The purpose of this experiment was to improve survival and growth ability of juveniles’ fish in brackish water during times of transition. The initial average weightes of Juveniles’ fish were 0.91±0.01 g (mean±SE). Experiments carried out in two phases. In step one, the Juveniles’ fish were kept for 15 days in fresh water and fed with commercial diet plus NaCl supplement (control without NaCl supplement, 5, 7 and 10 percent) in four treatments, each treatment inclusive three replication. In the second step, the fish transferred to brackish water (12.5 psu) and fed for 28 days with a commercial diet (without NaCl supplement). The results showed that no change compared to control treatment in renal tissue in step one. The difference between the kidneys were not in fish fed with NaCl supplement and without it. Nevertheless, a significant difference was observed between the size of the glomeruli and renal tubules between fresh and brackish water environments (between stage one and two), (P<0.05). In step one, were observed in the gill accessory cells in treatments fed salt supplements. At the end of the second step, the number of gill chloride cells in fish fed with salt supplementation was more than control (P<0.05). In addition, the highest and lowest weight gain was obtained in treatment two and four respectively (P<0.05), and no significant difference was observed between control and treatment 3 (P>0.05). The results showed that the fish fed dietary supplements of sodium chloride 10% versus the control treatment had less weight gain. Therefore, the was obtained the highest weight gain and growth performance (condition factor, specific growth rate) and the highest feed efficiency and protein efficiency ratio and the lowest feed conversion ratio in treatment 2 with the feeding of 5% NaCl in dietary supplements.