Effect of long-term oral administration of beta-glucan as an immunostimulant or an adjuvant on some non-specific parameters of the immune response of turbot Scophthalmus maximus

Abstract

A commercial P-glucan known for its ~mmunostimulatory effects in several fish species was tested in turbot ScophthalniusmaximusL.. both as an oral immunostimulant and as an adjuvant for oral vaccination. Some non-specific immune parameters were tested after a 5 wk feeding period with a commercial diet mixed with yeast P-glucan. Furthermore, during the last 5 d of the feeding period, half of the fish were orally vaccinated by mixing the commercial pellets with an anti-vibriosis vaccine (Vibriffa bain ND). The oral administration of P-glucan induced no reduction in mortality after a challenge with a virulent Vibrio anguillarum (strain 408). In contrast, a single oral vaccination resulted in protection against V anguillarum. The use of P-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 P-glucan. The plasma complement activity was not influenced by any of the treatments. In contrast, lysozyme activity was enhanced after administration of the adjuvanted vaccine. An increase in the chemiluminescent response of opsonised zymosan-stimulated head-kidney leucocytes was less obvious and no significant results were recorded.