INFLUENCE OF LONG-TERM HYPOXIA EXPOSURE ON THE ENERGY-METABOLISM OF SOLEA-SOLEA .2. INTERMEDIARY METABOLISM IN BLOOD, LIVER AND MUSCLE

Eutrophication of the Northern Adriatic Sea results in regular and long periods of hypoxia and occasional anoxia. Thus, animals living in this area must be well adapted to these conditions, including sole Solea solea, a flatfish living on sandy bottoms. Healthy sole were kept in aquaria at 20 degrees C for at least 2 mo. The fish were exposed to hypoxia after a preacclimation period of 30 h at normoxia. During normoxia oxygen levels were kept constant at 80% air saturation, during hypoxia they were set at 60, 40, 20, 12 or 6% air saturation. Control experiments were carried out at 100% air saturation. After conditioning the fish were anaesthetized and blood, muscle and liver samples taken. In the extracts of freeze-clamped tissues, 12 components of energy metabolism were measured in muscle, 11 in liver. Between 100 and 20% air saturation no major changes in metabolite concentration were found, while at 12 and 6% important changes were observed. Lactate levels increased in all tissues, particularly in blood, where, unexpectedly for flatfish, high concentrations were found (up to 19.8 mM). ATP declined in liver and blood, but not in muscle where the decrease in phosphocreatine appeared to be sufficient in stabilizing the ATP level. Total anaerobic energy production, calculated from changes in metabolite concentrations, amounted to 52 and 148 pmol ATP 100 g(-1) h(-1) at 12 and 6% air saturation, respectively. At these oxygen levels total metabolism was depressed by 27 and 48%, indicating that metabolic depression is a more effective survival strategy than the induction of anaerobic metabolism.