The zebrafish were statically exposed to Cd and Zn in glass aquaria (500 ml water) with net baskets, in order to prevent the fish from being contaminated by Cd adsorbed on faeces accumulating on the bottom of the aquarium. This procedure has previously been shown to minimize the Cd input to the gastrointestinal tract, within levels expected from the low drinking rates reported for freshwater fish (Wicklund Glynn and. Olsson, 1991) . The Zn and Cd concentrations were varied by addition of 〖ZnSO〗_4 and 〖CdNO〗_3 , respectively (analytical grade, Merck, Germany) , together with a constant amount of radioactive CdCl. The specific activity of Cd in the
water varied from 6x〖10〗^6Bq 〖nmol 〗^(-1)Cd at 0.1 nM Cd to 1x10 3 Bq nmol-1 Cd at 600 nM Cd.