Starved and fed carp (Cyprinus carpio) were exposed to sublethal waterborne copper exposure (1 microM) for 28 d in softened Antwerp, Belgium, city tap water. Copper accumulation in liver and gill tissues was determined, and changes in branchial Na+/K+-adenosine 5'-triphosphatase (ATPase) activity and metallothionein (MT) induction in gill and liver tissues were investigated following 28-d copper exposure. Gill Na+/K+-ATPase activity in exposed fish, both starved and fed, was at its lowest values after 3 d of exposure, after which it slowly recovered to preexposure values. No significant differences in branchial Na+/K+-ATPase activity were found between starved and fed fish. Copper accumulation in the liver and gills of the exposed starved carp was significantly higher than that in the exposed fed carp. The highest MT induction was found in liver tissues. Different patterns of MT induction were observed in the starved and fed carp during copper exposure. Before exposure, MT concentrations in the livers of the starved fish were significantly higher than those in the fed ones. Copper exposure significantly increased MT concentration in the liver of the fed fish, but no changes occurred in the starved fish. In contrast, copper exposure increased MT concentrations in the gills of the starved fish during the first week of exposure, whereas only a slight increase in MT concentration in the gills of the fed fish was observed. When taking into account the role of feeding status in MT induction, hepatic MT was a more relevant indicator for long-term monitoring of copper pollution in carp, but gill MT provided useful information regarding short-term copper toxicity.