Effect of Dietary Sodium Chloride on Growth of Atlantic Salmon (Salmo salar)

Abstract

Growth and food conversion efficiency in Atlantic salmon smolts (Salmo salar) in either fresh water or sea water were not demonstrably affected by varying the level of dietary sodium chloride. Large dietary salt loads were almost completely absorbed from the gastrointestinal tracts offish within 24 h, and plasma sodium and chloride concentrations were positively affected at this time.Irrespective of whether fish were undergoing random, spontaneous activity or an enforced, uniform low level of activity, growth rates and food conversion efficiencies were similar when fish were fed the same ration but different amounts of sodium chloride.A possible explanation is that normal renal function in fresh water provides for large amounts of hypoosmotic urine in which excess sodium chloride may be discharged without great expenditure of energy. However, in sea water, where urine flow is minimal, the main route of excretion for the excess electrolytes is across the gills, a process requiring energy.