THE EFFECT OF SUBLETHAL LEVELS OF COPPER ON OXYGEN-CONSUMPTION AND AMMONIA EXCRETION IN THE COMMON CARP, CYPRINUS-CARPIO

Common carp (Cyprinus carpio) of 15-30 g body weight were exposed to copper levels of 0.22 +/- 0.07, 0.34 +/- 0.12 and 0.84 +/- 0.35 mu mol . l(-1). Oxygen consumption and nitrogen excretion were determined repeatedly for up to 2 weeks of exposure to copper. Critical oxygen concentrations for oxygen consumption as well as for ammonia excretion were determined after 1 week of exposure to copper. Oxygen consumption dropped significantly immediately after exposure to 0.34 and 0.84 mu mol . l(-1) of copper whereas nitrogen excretion remained stable. After 1 week of continuous exposure to 0.34 mu mol . l(-1) of copper the oxygen consumption showed an apparent recovery, while the ammonia quotient (AQ = mole to mole ratio of ammonia excreted to oxygen consumed) did not, At a copper concentration of 0.84 mu mol . l(-1), no recovery was observed. The critical oxygen concentration for oxygen consumption shifted from 45 mu mol . l(-1) (1.4 mg . l(-1)) in copper-free water to 126 mu mol . l(-1) (3.9 mg . l(-1)) at a copper concentration of 0.34 mu mol . l(-1). At 0.84 mu mol . l(-1), regulation of oxygen consumption was lost. Also ammonia excretion showed a decline at lower oxygen concentrations and a critical oxygen concentration for ammonia excretion was determined. For the nitrogen excretion, loss of regulation already occurred at copper concentrations of 0.34 mu mol . l(-1). For the AQ, no critical oxygen concentration was found. The results obtained in this study suggest that measurements of oxygen consumption in combination with measurements of nitrogen excretion can be useful indicators of stress, Furthermore, it is shown that a critical oxygen concentration for ammonia exists in carp and that the critical oxygen concentrations for oxygen consumption and for ammonia excretion are affected by exposure to copper.