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 based on cod muscle meal as a Protein source for 8 weeks. The basal diet contained 17 mg Zn/kg to which 0, 10, 20, 40 or 80 mg Zn/kg diet, respectively, were added as ZnSO4. 7H2O. After 8 weeks, 15 fish from each 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. Blood samples were withdrawn and serum was analyzed for zinc concentration and alkaline phosphatase (AP) activity. Liver, kidney, vertebrae and intestine were removed from ten fish in each dietary treatment. A further ten fish were used for whole body mineral analyses. There were no significant differences in growth due to different dietary zinc concentrations and this, together with data on alkaline phosphatase and iron levels, showed that the basal diets contained sufficient zinc to prevent overt zinc deficiency symptoms. Zinc concentrations in the whole body and tissues, however, were significantly influenced by dietary zinc level. On the basis of the dietary zinc concentration required to maintain whole body zinc and serum zinc concentrations within the normal range, it was concluded that the dietary zinc requirement of juvenile Atlantic salmon is between 37 and 67 mg Zn/kg dry diet under our test conditions. Hence, until more data are available, juvenile Atlantic salmon diets based almost entirely on marine fish protein should contain > 67 mg Zn/kg dry diet.