Changes in Prochilodus scrofa gill tissue and in blood responses were investigated after 96-h copper exposure and transference to clean water. Gill damage was characterized by epithelial lifting, cell swelling, pavement, chloride and mucous cell proliferation, and blood vessel anomalies. Restoration of gill structure was slow, with no tissue improvements in the first 2 days in clean water. From the 7th to the 15th day, the recovery of gill tissue began to become evident, with complete recovery occurring on the 45th day in clean water. Hematocrit, red blood cells, and hemoglobin concentration showed a significant increase after copper exposure, remaining high until the 7th day after transference to clean water. Plasma Na(+) and Cl(-) concentration decreased significantly and K(+) increased significantly after copper exposure and, on the 7th day in clean water, plasma ions showed no significant difference from those in control fish. Gill tissue restoration took longer than the recovery of blood parameters, possibly implying extra energy needs, which may be critical, depending on the fish's life cycle.