systems (Davis et al., 2002). There are two ways to increase the immunocompetence of fish: vaccines and immunostimulation. Vaccinations have been reported as the most effective prophylactic method of controlling disease in fishes, but they are limited to only a small range of pathogens. Furthermore, an immediate control of an unknown disease agent is not possible through vaccination (Sakai, 1999). Preventive and management measures are central concern to overcome such outbreak of diseases and an important part of feed formulation is to include ingredients that assist in meeting the everyday challenges caused by stress episodes or to prevent effects after the eventual occurrence of pathogens. In this context, dietary immunostimulants are considered as an effective tool for enhancing the immune status of cultured organisms and improving their general welfare (Dimitroglou et al., 2009;