Effects of dietary zinc levels on zinc concentrations in tissues of common carp.

Common carp always has higher zinc concentration in viscera than other carps. To determine the relationship between the dietary zinc level and zinc concentration in common carp, the fish were fed diets containing 17, 294, 1,007 and 1,974 ppm zinc for 8 weeks, and the zinc concentration in each tissue was measured. It was found that the group of fish fed 17 ppm zinc had the highest growth rate. When the dietary concentration of zinc was lower than 294 ppm, the zinc concentrations in the tissues were similar during the 8 weeks of experiment. The zinc accumulated in the fish when the dietary zinc concentration was higher than 1,007 ppm. Zinc accumulated first in the digestive tract, then in the skeletal tissues and then in skin and muscle. Common carp and silver carp were fed the same diet from hatchling till adult. The results indicated that no matter whether the feed was natural food or artificial feed containing 300 ppm of zinc or artificial feed containing 25 ppm of zinc, the zinc concentrations in common carp were several times higher than silver carp. We concluded that the fact that common carp had higher zinc concentrations than other carps was not caused by the diet, but might arise from the fact that the absorption rate of zinc was higher.