Water quality was investigated in shrimp culture areas in Cau Ngang, Tra Vinh where three culture systems were found in
the same area to assess the impact of intensification of shrimp culture on the surrounding environment. Three culture systems were selected including intensive, semi-intensive and rice-shrimp alternated culture for the study. Monthly assessment of physical and chemical parameters of water and biotic parameters were done for a period of one year from March, 2009 to February, 2010 in the canals surrounding the culture systems. The physical chemical parameters of water recorded include temperature, pH, dissolved oxygen, chemical oxygen demand (COD), total suspended solids (TSS), total ammonium (TAN), nitrite (N-NO2-), nitrate (N-NO3-) and total nitrogen (TN), total phosphorus (TP) in both water and sediment. Zooplankton and zoobenthos were determined
quantitatively and qualitatively using zooplankton nets and Petersen grabs, respectively. The results indicated that most of water
parameters were not significantly different between culture systems and were in suitable ranges for aquatic life within the national
standard criteria except DO, TSS and TP at some periods. DO concentration in rice-shrimp system was significantly lower than that in other systems. TSS and TP concentrations both in water and sediment were high exceeding the limit ranges (> 100 mg/L). The occurrence of some zooplankton and zoobenthos species indicated that all systems were polluted at ? level (mesosaprobic) in which the rice-shrimp alternated culture system subjected to more environmental fluctuation not only by shrimp culture but also rice cultivation and salinity variation between dry and rainy seasons.