EFFECTS OF COMBINED WATERBORNE CD AND CU EXPOSURES ON IONIC COMPOSITION AND PLASMA-CORTISOL IN TILAPIA, OREOCHROMIS-MOSSAMBICUS

Plasma ions and cortisol levels were studied in immature tilapia for 6 days to a range of sublethal concentrations of Cu (50, 100 and 200 mu g Cu l(-1)), Cd (20, 35 and 70 mu g Cd l(-1)) and to combinations of these metals (50 mu g Cu l(-1) + 20 mu g Cd l(-1), 100 mu g Cu l(-1) 35 mu g Cd l(-1) and 200 mu g Cu 1(-1) + 70 mu g Cd l(-1)). Our data show that Na and Ca were markedly, although not exclusively, affected by Cu and Cd, respectively, Plasma Na concentrations were most promine ntly decreased in Cu-exposed fish, with less pronounced effects in Cd- exposed fish, In fish exposed to 70 mu g Cd l(-1), the plasma Ca conce ntration was half of the control value, Cu-induced changes of plasma C a concentrations were less strongly marked, In combined Cu/Cd exposed fish, Na, Ca and Cl concentrations were significantly changed, Importa nt in the present study was the notion that, in combined Cu/Cd exposed fish, the changes in Na and Ca levels could not be explained by syner gism of addition of the effects observed in single metal exposed fish, Plasma cortisol levels were increased in Cu-exposed fish, but an incr ease was not observed in the Cu/Cd co-exposed fish, It is argued that the absence of this cortisol response contributes to an inadequate rec overy of ionic disturbances in the Cu/Cd co-exposed fish.