Effect of anaesthetics on stress physiology and welfare in sea bass Dicentrarchus labrax

Studies on anaesthesia are relevant for fish welfare. Anaesthetics are routinely used in aquaculture to minimize stress and to avoid injuries during transport, spawning, vaccination and handling, as well as to euthanize fish in an ethical way. Anaesthetics are also used during sampling procedures when physiological blood parameters are measured as welfare indicators in farmed fish (Huntingford et al., 2006). Prevention of hypothalamo-pituitary-interrenal axis activation through the use of effective anaesthetics is, therefore, of fundamental importance to minimize both stress during aquaculture practices and interferences of blood sampling on measurement of stress indicators. So far, several anaesthetics have been evaluated for aquaculture applications and research, of which the major one are tricaine methanesulphonate MS222, 2-phenoxyethanol, quinaldine, benzocaine and metomidate. However, none of these meet the characteristics of an “ideal anaesthetic” (Marking and Meyer, 1985) for sea bass. At present, only few data are available on two new chemical agents used for fish anaesthesia: clove oil (70-90% eugenol) and Aqui-S® (50% iso-eugenol). The efficacy of clove oil as an anaesthetic was recently evaluated in sea bass by Mylonas et al. (2005), but no data are available on its effects on stress physiology. There are no data on the use of Aqui-S® in sea bass. This study aims to compare the efficacy of MS222, 2-phenoxyethanol, clove oil, Aqui-S® and hypothermia as anaesthetics in sea bass and their potential stress-reducing capacity.