Haematological and phenoloxidase activity changes in the shrimpPenaeus stylirostrisin relation with the moult cycle: protection against vibriosis

This paper describes the changes in the total and differential haemocyte counts during the moult cycle of the shrimp,Penaeus stylirostris. Correlative measures of phenoloxidase (PO) activity and resistance to infection against vibriosis were also investigated during the moult cycle. Three types of cells are identified: hyaline cells (HC), which are small with a big nucleus, represent 80% of the total; semi-granular cells (SGC) represent 10–13%; and large granular cells (LGC) represent 4–10% of the total cells, being the largest cells with highly eosinophilic intracytoplasmic granules. Significant variations of total haemocyte count (THC) between intermoult and premoult were recorded; a minimum in the former and a maximum in the latter. The PO activity measured at the same time decreased during the moult cycle but when compared to the THC was higher at intermoult. The variations in PO activity were similar to those of the relative percentage of the LGC, showing its role in the prophenoloxidase system (proPO-system). The resistance to infection was studied by performing anin vitroassay. Experimental infection with a highly pathogenicVibrioAM23 was carried out by bathing selected shrimps in a concentration of 105cfu ml−1at intermoult and premoult. The mortality of shrimps in premoult was 48% while in intermoult the mortality was 21%. This indicated that shrimps infected in premoult were more sensitive to vibriosis than in intermoult. Further, the variations of selected parameters (i.e. THC, PO) seem to be consistent with thein vivoresponse against the highly pathogenicVibrioAM23.