Hundreds of fish and prawn farms were constructed in the past decades. Many of these farms have ceased operation mainly due to the outbreak of diseases. With population increase, rapid urbanization and industrialization, water quality at the estuary and coastal regions where most of the fish and prawn farms are located is deteriorating. Treatment and recycling of water are essential to maintain the water quality at an acceptable level. A system consisting of preliminary settling, biofiltration, secondary settling and final polishing with a biofilter was tested in an experimental farm. Water quality was maintained at relatively good level at the cultivating pond after 120-day growing period. The growing facilities continued to show good performances after 4 growing cycles with a 2-week rest period between each cycle. Similar system was installed at a 26-hectare farm site having several ponds with sizes varying from 0.7 to 2.5 hectares. No disease outbreak was encountered after the installation of the treatment and recycling facilities.

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