HEMATOLOGICAL AND PHENOLOXIDASE ACTIVITY CHANGES IN THE SHRIMP PENAEUS-STYLIROSTRIS IN RELATION WITH THE MOLT CYCLE - PROTECTION AGAINST VIBRIOSIS

This paper describes the changes in the total and differential haemocy te counts during the moult cycle of the shrimp, Penaeus siylirostris. Correlative measures of phenoloxidase (PO) activity and resistance to infection against vibriosis were also investigated during the moult cy cle. Three types of cells are identified: hyaline cells (HC), which ar e small with a. big nucleus, represent 80% of the total; semi-granular cells (SCTC) represent 10-13%; and large granular cells (LGC) represe nt 4-10% of the total cells, being the largest cells with highly eosin ophilic intracytoplasmic granules. Significant variations of total hae mocyte count (THC) between intermoult and premoult were recorded; a mi nimum in the former and a maximum in the latter. The PO activity measu red at the same time decreased during the moult cycle but when compare d to the THC was higher at intermoult. The variations in PO activity w ere similar to those of the relative percentage of the LGC, showing it s role in the prophenoloxidase system (proPO-system). The resistance t o infection was studied by performing an in vitro assay. Experimental infection with a highly pathogenic Vibrio AM23 was carried out by bath ing selected shrimps in a concentration of 10(5) cfu ml(-1) at intermo ult and premoult. The mortality of shrimps in premoult was 48% while i n intermoult the mortality was 21%. This indicated that shrimps infect ed in premoult were more sensitive to vibriosis than in intermoult. Fu rther, the variations of selected parameters (i.e. THC, PO) seem to be consistent with the in vivo response against the highly pathogenic Vi brio AM23. (C) 1997 Academic Press Limited.