Conclusions
Administration of glucans through various routes including immersion, feed or injection have been found to enhance many types of immune responses, resistance to bacterial and viral infections and resistance to environmental stress. Although the efficacy of the glucan to some extent varies with type and administration, glucan used as an immunomodulatory additive has been found to be active in eliciting immunity in commercial aquaculture[
100] and is currently routinely used in commercial farming. Development of more efficient administration methods will facilitate the routine and prophylactic use of glucans as natural immunostimulants of fish. Lately, interest focused on mechanisms of action. However, nothing conclusive can be reached as a result of these studies and the effects of glucan on modulation of gene expression leading to stimulation of fish immunity still require elucidation. Therefore, the limited knowledge of mechanisms of glucan action on fish immunity does not currently allow better and more specific use of glucan in aquaculture.