The effect of starving and feeding on copper toxicity and uptake in Cu acclimated and non-acclimated carp

Common carp (Cyprinus carpio) were fed two different food rations: 0.5% body weight (low ration, LR) and 5% body weight (high ration, HR) and were either acclimated to sublethal copper (1 μM) for 28 days in softened Antwerp city tap water or not acclimated. Fish were exposed for 10 days to high Cu levels using four different concentrations (3.5, 6, 10, and 15 μM) before and after the Cu acclimation. Fish tolerance against Cu exposure was evaluated, and gill, liver, and carcass Cu and sodium levels were measured in dead and surviving fish. HR fish were twice as sensitive as LR fish in both tests. The 96 h median lethal concentration (LC50) values for the non-acclimated LR and HR fish were 8.46 ± 2.79 and 4.34 ± 0.82 μM, respectively. The fish became more resistant to low Cu concentrations after Cu acclimation and the LC50 values were slightly increased, reaching 9.20 ± 1.56 μM and 5.01 ± 1.93 in LR and HR fish accordingly. Cu concentrations in the gills, liver, and carcass were significantly elevated in response to the short-term Cu exposure, and were significantly higher in LR fish than in HR fish. High Cu levels caused a net loss of sodium resulting in a severe ion regulatory disturbance. The rate of sodium loss increased linearly with increasing exposure concentrations. Cu acclimation resulted in reduced sodium loss and increased the resistance and tolerance to Cu toxicity.