Changes in water quality characteristics of semi-intensive and modified extensive type aquafarms in Nagapattinam coastal area were studied for three crop periods to assess the impact of farm effluents in the nearby water bodies. The pH of the pond water steadily increased from early phase to harvest period both in extensive and semi - intensive farms. The salinity did not show much variation from inlet to outlet. The dissolved oxygen level of outlet water was found to be 40% less than the inlet water. The concentration of ammonia and nitrate in aquafarm discharges were slightly higher in semi-intensive farms when compared to extensive farms. The concentration did not cause any eutrophication or planktonic bloom in and around the farming area indicating that its environmental impact is very less. The biological oxygen demand, chemical oxygen demand and hydrogen sulphide values were within the permissible level in both extensive and semi-intensive farms.

Aquaculture, Water quality in aqua ponds and impact of effluent discharge.