Accumulation of zinc from diet and its release in common carp

High zinc diet of 2000 mg kg(-1) was fed to common carp (Cyprinus carpio), grass carp (Ctenopharyngodon idellus) and tilapia (Oreochromis aureus) for 8 weeks to compare the accumulation of Zn in fish. It was found that accumu lation of zinc from diet by grass carp and tilapia was low when compared to common carp. The largest difference occurred in digestive tract tissue. Th e digestive tract tissue of common carp had a large pool of stored zinc, th e mean 'storable capacity' is about 1500 mu g Zn g(-1) fresh tissue, and th e time needed to saturate the tissue when feeding 2000 mg Zn kg(-1) diet is about 8 weeks. The accumulated Zn in the digestive tract tissue of common carp was released when the dietary Zn was reduced to normal level (50 mg kg (-1)) or deficient level (4 mg kg(-1)) for 4 weeks. Subcellular fractionation results indicate that Zn accumulated in digestive tract tissue of common carp was accumulated mainly in the nuclei/cell debr is fraction. Exposure to a high Zn diet induced some metallothionein-like s ubstance in the digestive tract tissue and the hepatopancreas of common car p, but the amount was very low when compared with the amount of Zn accumula ted in the nuclei/cell debris fraction.