Annual variations of the plasmatic levels of glucose and amino acid and daily changes under different natural conditions of temperature and photoperiod in Gilthead Sea bream (Sparus aurata, L.).

Daily and annual changes in the plasmatic glucose and amino acid concentration have been determined in Sparus aurata L. Fish (average weight 330 g) were kept in cages under natural conditions of temperature and photoperiod and fed with a commercial diet. The months studied were chosen to establish whether there is any influence on the plasmatic glucose and amino acid concentration due to the change in temperature and photoperiod (equal photoperiod and different temperature, March and October; different photoperiod and equal temperature, May and November; and different photoperiod and temperature, June and January). To study the daily profile of glucose and amino acids concentrations, blood was extracted from six fish every 3 h during 24 h. Annual changes were determined as the average of the samples obtained during 1 day. Results show an annual rhythm with acrophase in June with a positive correlation with photoperiod for glucose and amino acids and with temperature only for amino acids. Daily profiles are rhythmical with a period of 24 h except in November with a period of 8 h for amino acids.