Metabolic depression and investigation of glucose/ethanol conversion in the European eel (Anguilla anguilla Linnaeus 1758) during anaerobiosis

The European eel (Anguilla anguilla Linnaeus 1758) is an important commercial fish species for aquaculture and fisheries. In aquaculture, one of the main hazards for the farmer is low oxygen condition due to technical disturbances or calamities. Therefore, in this study, we investigated the tolerance and metabolic response of European eel to anoxic conditions. In a 1 l flow-through Sétaram microcalorimeter we measured a 70% reduction of the Standard Metabolic Rate (SMR) during a period of 1 h anoxia, a process called metabolic depression. This strategy has the advantage that the survival time during anaerobioses can be extended because of a reduction of energy consumption and reduction of end product accumulation. Correcting for the time constant of the calorimeter by deconvolution techniques (time lag correction), we could describe the dynamics of the process of metabolic depression in European eel. From the deconvoluted signal it can be concluded that the 70% metabolic depression of European eel under anoxia takes place within 30 min. In parallel asphyxia experiments with European eel, no increased levels of ethanol were observed in blood plasma or ambient water. Ethanol concentrations in blood plasma were even significantly lower in the asphyxia group, probably indicating a decreased microbial activity. The 18-fold increase of plasma lactic acid is indicative for activation of Embden–Meyerhof glycolysis during anaerobioses.