Influence of long-term hypoxia exposure on the energy metabolism of Solea solea. I. Critical O2 levels for aerobic and anaerobic metabolism

Abstract

Long-term hypoxia is a general phenomenon on the Italian Adriatic coastline, and is mainly caused by continuous eutrophication. The sensitivity of sole Solea solea to long-term hypoxia was investigated. Healthy S. solea obtained from trawls were kept at 19 °C in aquaria for at least 2 mo. The fish were exposed to hypoxia after a preacclimation period of 30 h at normoxia. Oxygen levels during normoxia were kept constant at 80% air saturation (16.6 kPa, 6,4 mg l-1 O2); during hypoxia oxygen levels were set at 60, 40, 20, 12 or 6% air saturation (4.8, 3.2, 1.6, 1.0, 0.5 mg l -1). During the experiment oxygen consumption was measured continuously. At the end of each experiment, blood samples were taken from anaesthetized specimens. Oxygen consumption patterns were statistically analyzed. A novel technique is described for the determination of the standard metabolic rate and the scope for activity of free-swimming animals. The resting metabolic rate and the scope for activity showed significant changes at reduced oxygen levels. Activity levels declined progressively starting at 40 % air saturation. Resting levels remained constant between 80 and 20 % air saturation, but fell below the standard metabolic rate at 12 and 6%. Blood lactate levels were increased at 12 and 6%, indicating anaerobic metabolism. Data show that 40% air saturation should be considered as a limiting level, while the incipient lethal level lies between 12 and 20%. © Inter-Research 1994.