ASSESSMENT OF ZINC STATUS IN JUVENILE ATLANTIC SALMON (SALMO-SALAR) BY MEASUREMENT OF WHOLE-BODY AND TISSUE-LEVELS OF ZINC

Duplicate groups of 40 g Atlantic salmon were fed dry pelleted diets b ased on cod muscle meal as a Protein source for 8 weeks. The basal die t contained 17 mg Zn/kg to which 0, 10, 20, 40 or 80 mg Zn/kg diet, re spectively, were added as ZnSO4. 7H2O. After 8 weeks, 15 fish from eac h dietary treatment were marked and then they were fed the basal diet for another 4 weeks. Fish were sampled after 2, 4, 8 and 12 weeks. Blo od samples were withdrawn and serum was analyzed for zinc concentratio n and alkaline phosphatase (AP) activity. Liver, kidney, vertebrae and intestine were removed from ten fish in each dietary treatment. A fur ther ten fish were used for whole body mineral analyses. There were no significant differences in growth due to different dietary zinc conce ntrations and this, together with data on alkaline phosphatase and iro n levels, showed that the basal diets contained sufficient zinc to pre vent overt zinc deficiency symptoms. Zinc concentrations in the whole body and tissues, however, were significantly influenced by dietary zi nc level. On the basis of the dietary zinc concentration required to m aintain whole body zinc and serum zinc concentrations within the norma l range, it was concluded that the dietary zinc requirement of juvenil e Atlantic salmon is between 37 and 67 mg Zn/kg dry diet under our tes t conditions. Hence, until more data are available, juvenile Atlantic salmon diets based almost entirely on marine fish protein should conta in > 67 mg Zn/kg dry diet.