Effect of oral administration of glucans on the resistance of gilthead seabream to pasteurellosis

dThe present study evaluated the effect of oral administration of three types of glucan on the resistance of gilthead seabream to Photobacterium damselae subsp. piscicida and on the activity of its phagocytes. Groups of fish were fed with a basal diet (controls) or with the basal diet supplemented with glucan for two different periods of time before being bath challenged with the bacterium. Groups of fish fed with 1 and 10 g kg(-1) of glucan for a short period (2 weeks with glucan and 1 week with the basal diet) showed a higher degree of protection against pasteurellosis than the control group. This was especially pronounced in groups of fish fed with the higher concentrations of glucan. The respiratory burst and phagocytic activity of spleen phagocytes varied with time but no significant differences were found between groups in the third week when the challenge was carried out. The group of fish fed with 1 g kg(-1) of glucan for longer periods of time (2 weeks with glucan, 1 week with the basal diet, 2 weeks with glucan, and I week with the basal diet) also showed enhanced protection against P damselae. However, the group fed with 5 g kg(-1) had mortality rates comparable to the control group, and protection in the group fed with 10 g kg(-1) of glucan was significantly lower than in the control group. These results suggest that glucans can be used in the diet to prevent or reduce mortalities in gilthead seabream due to pasteurellosis, and they show the importance of the concentration and the period of administration of glucan to obtain optimal protection against this disease. (C) 2003 Elsevier Science B.V. All rights reserved.