High Zinc Supplementation of Rainbow Trout Diets

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Abstract
Zinc in the form of zinc sulfate or chelated as zinc proteinate was fed in increasing levels (4 to 1,700 µg/g zinc) in an egg-white based diet to fingerling rainbow trout (Salmo gairdneri) to determine potential toxicity. Zinc sulfate was fed for the first 55 days and zinc proteinate for the last 118 days of a 173-day test. Fish fed the lowest level of zinc (4 µg/g zinc, a zinc-deficient diet) had poor growth and high mortalities, while the lowest level of added zinc (90 µg/g) reduced mortalities and markedly improved growth. Higher levels of supplemented zinc, up to 1,700 µg/g, had no further effect on growth or survival. Zinc concentration in liver, blood, and gills increased with dietary levels of zinc above 90 µg/g. Trout showed no signs of zinc toxicity during feeding with levels of dietary zinc as high as 1,700 µg/g.