The present study was conducted in order to monitor the presence of in extensive and modified extensive shrimp culture systems. In extensive system, count ranged from 180 to 380 cfu ml-1 and 187 to 668 ml in modified extensive system. In the present study sediment registered highest load in both systems (1725-2708 cfu g and 2019 to 5699 cfu g ). In extensive system, percentage distribution of in water was 6.5, 7.2 and 16.6%, respectively, for pre monsoon, monsoon and post monsoon. In, modified extensive system, in water, percentage distribution of V.