Metabolic adjustments in the common carp during prolonged hypoxia

Biochemical and respiratory changes in the common carp Cyprinus carpio were studied 6, 24, 96 and 168 h upon exposure to hypoxia (0.5 mgO(2) 1(-1)). M odification of kinetic properties of phosphofructokinase (PFK-1), coupled w ith a decreased in PFK-1 activities, were evident in muscle. No changes in kinetics and activities could be observed in muscle pyruvate kinase (PK) an d lactate dehydrogenase(LDH). A decrease in muscle citrate synthase (CS) an d an increase in muscle cytochrome c oxidase (CCO) were found. The common c arp was able to maintain a constant level of muscle glycogen, muscle ATP, a nd liver CS throughout the 168-h experimental period. Changes in activities of liver LDH and muscle CCO were observed only at 168 h, which indicates t hat common carp may switch to alternative metabolic pathway to deal with pr olonged hypoxia. A severe decrease in liver glycogen was accompanied by inc reases in lactate levels in both the muscle and liver. Oxygen consumption r ate was reduced under hypoxia, but resumed to normoxic levels within 2 h up on return to normoxic condition. Overall, these results indicate that carp adopt different strategies in an attempt to deal with short term and long t erm hypoxia in the natural environment. (C) 2000 The Fisheries Society of t he British Isles.