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Phenoloxidase is a key enzyme in the innate immunity of the crab. It protects the animal from injury,
infection, hardening of exoskeleton and melanisation. Whereas Lysozyme is a bacteriolytic enzyme
secreted by host during phagocytosis. It is one of the important enzymes in the innate immunity of
the crab against gram positive and gram negative bacteria. In this study we have studied that
Phenoloxidase activity increased from 2hrs to 48 hrs after challenge with gram positive and gram
negative bacteria in case of male crabs. In case of female crabs challenged with bacteria,
phenoloxidase activity gradually increased from 2hrs to 48 hrs of post bacterial inoculation. The
results of the present study revealed that the enzyme activity in hemolymph of bacterial challenged
crabs was highest in all time points than control and control injured crabs. The zone of inhibition
increase gradually from 2hrs to 12 hrs in Klebsiella challenged male crab and female crab and also
in male and female crabs challenged with Bacillus. The protein band observed at 16 kDa was
identified as Lysozyme and 67kDa as Prophenoloxidase.
Keywords: Prophenoloxidase, lysozyme, antimicrobial studies, Scylla Serrata