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Viewed : 4927 - Downloaded : 3938 With the aim of finding the optimum concentration of waterborne sodium for use during egg incubation period and higher production of the rainbow trout larvae in a water recirculation system, a completely randomize experiment was conducted. The effect of different levels of waterborne sodium (2, 14, 50 and 100 mg L^-1) on eye pigmentation, hatching rates, ions (Na, K, P, Cu, and Mn) and water content of eggs in rainbow trout fish, Oncorhynchus mykiss, were determined. The newly fertilized eggs were introduced in water recirculation incubators as experimental units. The water temperature was between 7.5-9 °C during the incubation period. In treatments with Na+ concentration of 2 and 14 mg L-1, hatching rates were significantly (P<0.05) higher than other treatments. Increase of waterborne Na⁺ up to 100 mg L^-1 significantly (P<0.05) decreased eye pigmentation. In all the treatments, water content (%) of egg, compared to the newly fertilized egg significantly (P<0.05) decreased at the hatching time. Egg ions content showed that the elevation of Na⁺ level to 14 mg L^-1 motivate sodium uptake by eggs from water and highest sodium uptake occurred in treatment with [Na⁺] 100 mg L^-1. In all the treatments, potassium uptake occurred by eggs from environmental water. Egg potassium content in [Na⁺] 100 mg L^-1 was significantly (P<0.05) higher than other treatments. In treatments with [Na+] 50 and 100 mg L^-1, prevention of Cu uptake by egg from ambient water occurred. Mn uptake by egg from water was only recorded in treatment with [Na⁺] 2 mg L^-1. An increase in phosphorus content of the eggs was also recorded in treatments with [Na⁺] 50 and 100 mg L^-1. It was concluded that eye pigmentation, hatching rates and ions content of rainbow trout eggs depend on the rate of waterborne sodium and concentration of 14 mg L^-1 can be introduced as a standard level, for hatching the rainbow trout eggs in a water recirculation system Keywords : Rainbow trout, egg, hatching rate, waterborne sodium, ion content