Capacity for thermal acclimation and winter mortality of sea bass Dicentrarchus labrax in freshwater earthen ponds

Some fish species exhibit a biochemical response to low winter temperatures. For example, after a period of cold acclimation, an increase in enzyme activity occurs. This can result in at least partial compensation in the rate of biochemical reactions of aerobic metabolism. Sea bass (Dicentrarchus labrax L. 1758) is a commercially important fish for the Mediterranean mariculture industry, which can grow satisfactorily in both freshwater (FW) and seawater (SW) conditions. The purpose of the present work was to evaluate the survival and growth of sea bass in FW earthen ponds. The experiment was initiated in September 2003 in order to avoid the water temperature highs during spring-summer and allow several weeks for acclimation before the winter temperature lows. Fish growth occurred for several months, but by the end of December 2003, ambient water temperature reached levels below 5°C and mass mortality occurred. The capacity of sea bass for thermal compensation was evaluated by monitoring the activity of cytochrome c oxidase (CCO) of red axial muscle. The activity of CCO initially increased from 6.4 (±0.98) in September (ambient water temperature 19°C) to 10.4 (±1.49) in October (ambient temperature 15.4°C), but decreased again to 8.8 (±1.45) in November (ambient temperature 12.3°C). A similar trend was exhibited by the glycolytic enzyme lactate dehydrogenase in white muscle. The results do not indicate a capacity of thermal acclimation in FW ponds with low temperature (