Abstract
The defense system of crustaceans mainly consists of two parts : cellular defense system and humoral defense system. Hemocytes and resident phagocytes are well known as cellular defense factors which have a high phagocytic activity. Nodulation and encapsulation are also reported as a celluler defense phenomenon. Factors concerning the humoral defense system include phenoloxidase (PO), the prophenoloxidase (proPO) activating system, bactericidin and lectins.
These defense factors in the cellular and humoral systems cooperatively provide a defense barrier against invading pathogenic organisms from the environment. These systems have a mutual interaction and construct an elaborate network of host immunodefense system. However under aquaculture condition, various stresses caused by high stocking density and resultant environmental pollution with organic matter damage the host defense system resulting in an increased susceptibility to infection.
In an attempt to prevent bacterial infection in crustacea, vaccination trials have been carried out successfully in shrimp, lobster and crayfish. Oral administration of immunopotentiators, such as β-1, 3-glucan and peptidoglycan, to shrimp increased the phagocytic activity of hemocytes and resistance against bacterial infection.
