Metabolic rate and tissue reserves in gilthead sea bream (Sparus aurata) under thermal fluctuations and fasting and their capacity for recovery

To differentiate between cold and fasting effects on gilthead sea bream (Sparus aurata) physiology, three conditions (cold-induced fasting at 8°C, cold group; forced fasting at 18°C, fasting group, and cyclic thermal fluctuations between 16°C and 8°C, fluctuating group) were compared with a control group (feeding at 18°C). Oxygen consumption rate, plasma lipid fractions, and tissue composition were analysed either during long exposure (5 weeks) or after 20 days of recovery. Sea bream showed strict thermoconformism in metabolic rate and feeding, and all groups, after changes, mobilised perivisceral fat. The fasting group also consumed other tissue reserves sequentially, except nonpolar lipids in liver. In the cold group, this liver lipid fraction increased twofold, but in the fluctuating group, food intake was gradually restored during each short period of higher temperature, and the steatotic livers caused by cold were not seen. During recovery, the fasting group showed the highest growth rate and deposition of reserves, whereas the cold group, although they mobilised liver lipid, did not grow. Appropriate management of the transient short periods of higher temperature may improve recovery from the cold season in gilthead sea bream culture.