Absorption, body distribution, and excretion of dietary zinc by rainbow trout (Salmo gairdneri)

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Abstract
Rainbow trout (Salmo gairdneri) were held in metabolizable energy chambers at Standard Environmental Temperature (15°C) for 72h following a single feeding of a semi-purified test diet containing tracer quantities of a radioisotope of zinc (65Zn) and different combinations of dietary calcium level and zinc source. Gill wastes, urine, and feces were separately collected. After 72h, the fish were killed, and samples of the following tissues removed: eyes, skin, muscle, blood, bone, liver, bile, kidney, gill, spleen, stomach, pyloric caeca, intestine, gonad, and remaining carcass. Radioactivity in the tissues and wastes was determined and the body distribution of the ingested zinc was quantified. Approximately 58% of the administered dose of65Zn was recovered. Of the recovered dose, 43.2% was present in the gastro-intestinal tract, 27% in the feces, 14% in the gill water, 16% in the body of the fish, and less than 1% in the urine. Of individual tissues, the gill, liver, kidney, and spleen had concentrations of65Zn higher than blood, while the remaining tissues had lower concentrations. Body and tissue levels were increased but not significantly by feeding65Zn as an amino acid chelate, compared to feeding as inorganic65Zn, while dietary calcium level had no effect. The results of this study indicate that the gills play a major role in excretion of dietary zinc, while the urine plays a minor role.