The anti-VH activity of the ethanol extract of G. fisheri for
P. monodon postlarvae and juveniles was correlated with increased
total haemocyte counts, increased granulocyte counts, increased
PO and SOD activities and increased super oxide anion production.
All these parameters are parts of the anti-bacterial defense mechanism
in crustaceans [33]. Phenoloxidase (PO) is a key enzyme
involved in production of reactive oxygen species, antimicrobial
phenolic compounds and melanin in response to pathogens [33]
and a high PO activity index has been suggested to be an indicator
good defense capability in shrimp [34]. Since the PO response
originates from semi-granulocytes and granulocytes [34], higher
numbers are associated with higher potential for PO activity. Thus,
our results suggested that the ethanol extracts stimulated haemocytic
proliferation and differentiation. During bacterial infection,
haemocytes also ingest pathogens by phagocytosis and destroy
them in the cytoplasm by the production of reactive oxygen
species, superoxide anions, hydrogen peroxide and hydroxyl radicals
[35]. In addition, haemocytes produce SOD that catalyzes
superoxide anions to hydrogen peroxide that acts as a substrate for