EFFECT OF LONG-TERM ORAL-ADMINISTRATION OF BETA-GLUCAN AS AN IMMUNOSTIMULANT OR AN ADJUVANT ON SOME NONSPECIFIC PARAMETERS OF THE IMMUNE-RESPONSE OF TURBOT SCOPHTHALMUS-MAXIMUS

A commercial beta-glucan known for its immunostimulatory effects in se veral fish species was tested in turbot Scophthalmus maximus L., both as an oral immunostimulant and as an adjuvant. for oral vaccination. S ome non-specific immune parameters were tested after a 5 wk feeding pe riod with a commercial diet mixed with yeast beta-glucan. Furthermore, during the last 5 d of the feeding period, half of the fish were oral ly vaccinated by mixing the commercial pellets with an anti-vibriosis vaccine (Vibriffa bain ND). The oral administration of beta-glucan ind uced no reduction in mortality after a challenge with a virulent Vibri o anguillarum (strain 408). In contrast, a single oral vaccination res ulted in protection against V. anguillarum. The use of beta-glucan as an adjuvant did not reduce the mortality rate more than did the single vaccination. An increase in white blood cell count was observed after the administration of only beta-glucan. The plasma complement activit y was not influenced by any of the treatments. In contrast, lysozyme a ctivity was enhanced after administration of the adjuvanted vaccine. A n increase in the chemiluminescent response of opsonised zymosan-stimu lated head-kidney leucocytes was less obvious and no significant resul ts were recorded.