As B-glucan has been shown to increase immunity and survival in various juvenile(i.e. stage from metamorphosis to sexual maturity) and adult fish(i.e. sexually mature) both in freshwater and marine aquaculture species as well as in marine fish larvae(ie. the stage from hatching to metamorphosis[12] it has been suggested to be one of the most potent immune system enhancers in aquaculture 1191. In mammals but as well in fish B-glucan is detected by multiple pattern recognition receptors including tolllike receptors and complement receptor C3 120,21 but the main mammalian 6-glucan receptor dectin-1 could not be identified in fish. In both mammals and fish B-glucan recognition results in the activation of macrophages, which induces phagocytosis, leukocyte migration and the production of cytokines(e.g. IL 1, TNFa), nitric oxide(NO) and reactive oxygen species, as well as the enhancement of complement activity[21-30]. Recent studies in juveniles and adult fishes have for example shown that yeast B-1,3/1,6-glucan in form of MacroGard increases complement activity 131,321 and induced an anti-inflammatory effect 127] in carp(Cyprinus carpio) juveniles. In addition it was also shown that B-glucan can enhance growth and leucocyte infiltration into the epithelial layers of the gut of carp juveniles 133]. However, in juvenile turbot dietary MacroGarda did not increase protection against an infection with Vibrio anguillarum and complement and lysozyme activity were not influenced even though the white blood cell count was increased