Effect of temperature on copper toxicity and hematological responses in the neotropical fish Prochilodus scrofa at low and high pH

Copper sulfate has been widely used to control algae and pathogens in fish culture ponds. However, its toxic effects on fish depend not only on its concentration in water but also on water quality. The susceptibility of the neotropical freshwater fish Prochilodus scrofa to copper was evaluated at two temperatures with low and high water pH. Juvenile fish were acclimated at 20 and 30 degrees C and exposed to copper (static bioassay system) in water with pH 4.5 and 8.0. The 96 h-LC50 were determined at each temperature and pH, as were the hematological parameters. The 96 h-LC50 for copper (98 and 88 mu g Cu. L-1 in water with pH 4.5 and 16 and 14 mu g Cu L-1 in water with pH 8.0 for fish kept at 20 and 30 degrees C, respectively) was significantly dissimilar in pH 4.5 and 8.0, but no difference was found between 20 and 30 degrees C in the same water pH. At 20 degrees C, regardless of the water pH, the hematocrit (Hct) increased while the red blood cells (RBC) and hemoglobin (Hb) concentration decreased compared to control pH 7.0. Copper exposure in water pH 4.5 and 8.0 causes an increase on the Hct, RBC and Hb concentrations in relation to the controls pH 4.5 and 8.0. At 30 degrees C, the changes on the blood parameters depended on the water pH and, after copper exposure at low and high pH, the blood changes indicated more complex responses. The changes in hematological parameters of the fish, regardless of the pH and water temperature, indicate ionoregulatory or respiratory disturbances that imply an increase in energy consumption to restore homeostasis instead of other physiological functions such as weight gain and growth. (C) 2005 Elsevier B.V. All rights reserved.