INTERACTIONS BETWEEN COPPER AND CADMIUM DURING SINGLE AND COMBINED EXPOSURE IN JUVENILE TILAPIA OREOCHROMIS-MOSSAMBICUS - INFLUENCE OF FEEDING CONDITION ON WHOLE-BODY METAL ACCUMULATION AND THE EFFECT OF THE METALS ON TISSUE WATER AND ION CONTENT

Juvenile tilapia (Oreochromis mossambicus) were exposed for 96 h to ra nges of sublethal concentrations of Cu or Cd, under both fed and non-f ed conditions. Exposure to one metal (Cu or Cd) not only resulted in a n increased whole body content of the metal exposed to, but also influ enced the concentration of the other metal present in the fish. Furthe rmore, the total amount of Cu and Cd accumulated during exposure to he avy metals was influenced by the nutritional state of the fish. Beside s exposure to either Cu or Cd, fish were also exposed to mixtures of C u and Cd. Results indicated that accumulation during Cu/Cd co-exposure cannot be predicted by simple addition of the effects of single metal exposures. Obviously, complex interaction mechanisms are involved, as was concluded e.g. from the significantly decreased whole body Cd-con tent of Cu/Cd-co-exposed fish compared to the Cd-content of Cd-exposed fish. This phenomenon was observed in both fed and non-fed fish. Beca use ionic homeostasis is known to be affected by heavy metals, in this study also whole body water, calcium and sodium content in Cu and/or Cd-exposed fish were determined. The results indicate that also with r espect to these parameters the two metals interact. The effects on wat er and ion appear to be dissociated. The data reveal previously unreco gnized effects of interaction of the metals on whole body metal conten t, water and ion regulation.