Effect of Dietary Calcium Phosphate and Zinc Supplementation on Whole Body Zinc Concentration of Rainbow Trout (Salmo gairdneri)

Abstract

Groups of rainbow trout (Salmo gairdneri) were fed casein–gelatin diets supplemented with calcium phosphate (Ca₃(PO₄)₂) to produce dietary calcium and phosphorus levels of 1,2, or 4% and 0.9,1.5, or 2.4%, respectively (low, medium, or high calcium phosphate), and supplemented with 20 μg Zn/g diet as ZnSO₄, zinc proteinate, or ZnSO₄ + EDTA (1000 μg/g). Dietary calcium phosphate levels had no significant effect on weight gain of the fish, although the fish fed the high dietary calcium phosphate level were smaller than the rest. Dietary zinc supplementation had no effect on growth, but significantly increased whole body zinc levels in fish fed diets containing low or medium calcium phosphate. In fish fed diets containing low calcium phosphate, the zinc supplements all increased whole body zinc concentrations. In fish fed diets containing medium calcium phosphate, supplementation with zinc proteinate resulted in higher whole body zinc values than supplementation with other zinc sources. Dietary zinc supplementation did not increase whole body zinc concentrations above control levels in fish fed the experimental diets containing high calcium phosphate. We conclude that increased dietary levels of calcium phosphate reduced whole body zinc concentration of rainbow trout and that 20 μg Zn/g diet was insufficient to overcome this reduction at the highest dietary calcium phosphate level regardless of the form of zinc supplement used.