Dietary Zinc Requirement of Hybrid Striped Bass, Morone chrysops x Morone saxatilis, and Bioavailability of Two Chemically Different Zinc Compounds

Zinc is a trace mineral element that plays an essential role in numerous biochemical processes, and has been shown to affect growth and health of several fish species. However, the dietary zinc requirement of hybrid striped bass has not been defined. Therefore, a feeding trial was conducted to determine the dietary requirement for zinc by this fish and to compare zinc bioavailability of two chemically different forms (zinc sulfate and zinc proteinate). Six experimental diets were formulated with purified ingredients and supplemented with ZnSO4 to provide total zinc concentrations of 7, 12, 16, 26, 42, and 80 mg/kg diet which were determined by analysis. Each diet contained 32% crude protein, 6% lipid, and approximately 14.2 kJ of digestible energy per gram. The experimental diets were fed twice daily for 10 wk to triplicate groups of 15 hybrid striped bass initially weighing 0.86 +/- 0.05 g/fish in 38-L glass aquaria, connected as a recirculating system. Finally, after the feeding period, the fish were evaluated for weight gain, feed efficiency, protein efficiency ratio, and survival, as well as blood serum zinc, bone zinc, and hematocrit. All fish thrived during the feeding trial and not even the fish fed the basal diet displayed any apparent deficiency signs, although weight gain steadily increased with escalating levels of dietary zinc up to 42 mg/kg diet. On the basis of the most responsive indicators-bone zinc and serum zinc-the minimum dietary zinc requirement of hybrid striped bass was determined to be 17.0 and 17.3 mg Zn/kg diet, respectively, based on broken-line regression. This estimate is similar in magnitude to dietary zinc requirements reported for other fish species. In addition, the bioavailability of zinc proteinate versus that of ZnSO4 was estimated by deriving the ratio of the slopes of the regression lines fitted to bone zinc and serum zinc data. This analysis indicated that hybrid striped bass utilized zinc proteinate similar to 1.7 times more efficiently than ZnSO4.