Biochemical responses of juvenile European sturgeon, ( Huso huso ) to a sub-lethal level of copper and cadmium in freshwater and brackish water environments

In caspian sea basin, sturgeons spend the larval and juvenile stages in freshwaters of rivers and then, they migrate tobrackish waters of the sea where they grow and mature. with regard to the elevation of the metal concentrations incoastal waters and sediments of the caspian sea and its adjacent rivers, it is likely that juvenile sturgeon are exposed tosub-lethal levels of metals during seawater entry process. we compared the biochemical responses of juvenile europeansturgeon, (beluga, huso huso) exposed to a sub-lethal level of copper (cu, 20 ?g/l) and cadmium (cd, 300 ?g/l) infreshwater (fw, 0 ppt) and brackish water (bw, 11 ppt) for seven days. the results showed that the levels of plasmaglucose increased significantly in bw and in all metal exposed groups. also, plasma cortisol concentrations showedsignificant increases when juveniles were exposed to bw, cu(fw/bw) and cd(bw). the activity of liver superoxidedismutase (sod) decreased significantly in bw compared with fw. moreover, cu and cd exposure enhanced the activityof sod in bw, while sod did not show any changes in fw. the levels of tissue and plasma proteins as well as plasmatriiodothyronine (t3), thyroxine (t4) and liver catalase (cat) activity remained constant when animals were exposed tocu/cd in both fw and bw environments. our data indicate that exposure of juvenile beluga to bw stimulated thegeneral biochemical responses of stress such as cortisol and glucose, while sub-lethal exposure to cu and cd causedoxidative stress in bw environment but not in fw.