In decapod crustaceans, circulating haemocytes are generally classified into three types: hyaline, semi-granular and large granular cells [11]. Haemocytes are involved not only in phagocytosis but also in the production of melanin via the prophenoloxidase (proPO) system [12] and [13]. Both semi-granular and granular cells carry out the functions of the proPO system [12]. Phenoloxidase is the terminal enzyme in the proPO system and is activated by several microbial polysaccharides, including β-1,3-glucan from fungal cell walls