Glucose tolerance in gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax)

Glucose tolerance tests were performed with seabream and seabass. The fish were adapted to a practical diet (50% protein; 12% lipid) for three weeks and then, after being fasted for 24 h, injected intraperitoneally with 1 g glucose/kg body weight. Blood, liver and muscle samples were collected before and 1, 3, 6, 12, 24, 48 and 72 h after injection. In both species, an increase in plasma glucose level was observed after injection. In seabream, plasma glucose level reached a peak 1-3 h after injection, while in seabass the peak was reached 3-6 h after injection. The peak value was significantly higher in seabream than in seabass. In both species, plasma glucose levels returned to the initial values within 12 h after injection. In seabream, plasma triacylglyceride peaked 1 h after injection and thereafter started to decrease to the initial levels that were reached within 6 h after injection. In seabass, plasma triacylglyceride levels decreased after injection, starting to increase 3 h later. The peak value was attained 6-12 h after injection and the basal values were reached within 24 h after injection. During the first hour after injection liver glycogen content of seabream significantly decreased, while in seabass it significantly increased. In both species, 6 h after injection liver glycogen content started to increase to a peak value, which was reached 12 h and 24 h after injection in seabream and in seabass, respectively. The results of this study indicate that seabream and seabass were able to restore glucose levels within 12 h after being injected with 1 g glucose/kg body weight. These data also suggest that plasma triacylglyceride concentrations and liver glycogen content may be related to the mechanism of glucose regulation in both species. Glucose injection seemed to enhance catabolism of body stores in seabream and to stimulate anabolism in seabass.