Relative Contributions of Dietary and Waterborne Zinc in the Rainbow Trout, Salmo gairdneri

Abstract

Rainbow trout, Salmo gairdneri, were fed purified diets with zinc concentrations ranging from deficient to excessive (1, 90, 590 μg Zn∙g⁻¹) and simultaneously exposed to a range of waterborne [Zn] (7, 39, 148, 529 μg Zn∙L⁻¹). After 1 wk, fish fed the deficient diet, at ambient waterborne [Zn], had low plasma [Zn] which decreased further during the 16-wk experiment. Growth ceased after 12 wk; hematocrit and plasma protein were depressed. Both whole body [Zn] and body burden decreased by 16 wk, but most other elements were elevated. Increasing waterborne [Zn] alone increased plasma [Zn], whole body [Zn], and growth in a graded manner and normalized hematocrit, plasma protein, and other whole body elements. Increasing dietary [Zn] to 90 μg Zn∙g⁻¹ at ambient waterborne [Zn] prevented depression of plasma [Zn] and permitted normal growth and whole body [Zn]. Zinc uptake from water, probably across the gills, was independent of uptake from the diet since at any dietary [Zn], increasing the waterborne [Zn] resulted in increased whole body [Zn]. Even when dietary [Zn] was adequate, the waterborne contribution was as high as 57%, and 100% when the dietary [Zn] was deficient. There were no toxic effects on any of the variables measured.