Impacts of intensive shrimp cultivation on water quality in the Songkhla Basin, Thailand

Water quality in intensive shrimp culture ponds was examined during one 5-month grow-out period. The measured parameters included temperature, salinity, Secchi disk transparency, pH, dissolved oxygen (DO) , biochemical oxygen demand (BOD), ammonia-N, nitrate, phosphate, total suspended solids, chlorophyll a, and plankton abundance/composition. Most water quality parameters changed relatively little over time except for specific trends in BOD, NH₃, pH, and transparency. There were increases in levels of BOD (2.8 to 12.1 ppm) , and NH₃ (0.0 to 1.5 ppm); pH decreased from 8.8 to 7.3 and transparency decreased from 80 to 40 cm. DO levels were relatively unchanged and maintained at 6-10 ppm over the grow-out period. Other parameters were considered as optimum levels for tiger shrimp culture, such as temperature (25-32 C) and salinity (20-32 ppt). BOD was identified as the most significant (P value < .05) parameter that affected shrimp feed efficiency; as BOD levels increased, feed efficiency decreased. During the grow-out period, the blue-green algae Oscillatoria sp. and the "pennate" diatoms were the dominant groups in the phytoplankton community while nauplius and rotifers were dominant in the zooplankton community. Phytoplankton densities and chlorophyll a concentrations increased as the grow-out proceeded. There were no significant effects of water exchange practices on the water quality parameters throughout the grow-out period.