Combined effects of different food rations and sublethal copper exposure on growth and energy metabolism in common carp.

Common carp (Cyprinus carpio) were fed two different rations, 0.5% body weight (low ration; LR) and 5% body weight (high ration; HR), throughout acclimation, sublethal (64 microg/L) Cu exposure for 28 days, and a subsequent 2-week recovery period. Growth, liver water content, and liver energy stores were assessed during this period. Growth rates were elevated in HR fish compared to LR fish, as was the hepatic lipid content. This was associated with a higher water content in the livers of LR fish. Liver glycogen levels were similar in both feeding treatments and remained relatively stable during Cu exposure. Cu exposure caused a significant reduction in growth in both HR and LR fish. Reduction in growth coincided with significant changes in liver and blood composition. Liver lipid levels dropped significantly during the first days of the exposure in both feeding treatments, and the difference between LR and HR lipid levels disappeared during Cu exposure. During the first week of Cu exposure, the difference in liver water content disappeared as well, with a significant reduction of the water levels in the LR fish. A rise of hepatic protein was observed after 2 and 4 weeks of Cu exposure in the LR carp and after 4 weeks of exposure in the HR fish. Cu exposure led to pronounced increases in plasma ammonia concentrations in HR carp. Growth and energy stores recuperated during the 2-week recovery period in both feeding treatments. The observed changes during Cu exposure are probably related to physiological disturbances like hypoxia and stress, as well as an inhibition of ammonia excretion.