Copper induced alterations of biochemical parameters in the gill and plasma of Oreochromis niloticus

The main objective of this study was: to determine the effects of copper exposure on copper accumulated in branchial tissue, gill Na+/K+-ATPase activity and plasma Na+, Cl-, osmolality, protein, glucose and cortisol, in Oreochromis niloticus. Fish were experimentally exposed to 40 and 400 mu g L-1 of waterborne copper and sacrified after 0, 3, 7, 14 and 21 days. Copper accumulation and Na+/K+-ATPase activity were determined in branchial tissue, whereas osmolality, Na+, Cl-, protein, glucose and cortisol concentrations were measured in plasma samples. Gill copper accumulation increased linearly with exposure time and concentration, whereas gill Na+/K+ -ATPase activity was maximally inhibited after 3 days of exposure and showed a significant negative correlation with copper tissue levels. Plasma Cl- values decreased with time of exposure but only at 400 mu g L-1 of copper. Plasma Na+ protein and osmolality decreased with exposure time at the highest copper concentration tested, whereas at 40 mu g L-1 of copper this effect was only observed after 21 days of exposure. Plasma glucose and cortisol levels increased in a dose and time dependent manner, while showing complex fluctuations during the intermediate exposure times. In conclusion, copper induces an early maximum inhibition of gill Na+/K+-ATPase activity in O. niloticus. The subsequent slow decrease in ion plasma levels was related to compensatory mechanisms involving a non-specific stress response that appeared overcome at long-term exposures. (c) 2005 Elsevier Inc. All rights reserved.