Abstract: In the recirculating aquaculture system, setting up the artificial purification system consisting of aquatic plants, cured indigenous microbial communities and filter-feeding fish and shellfish, can reduce the nutrients in the aquaculture water, lighten the eutrophication level and increase the stability of water quality effectively. Comparing the major water quality index before the system set up and those after that, the results show that in 2008 without the system, the average annual value of PO₄-P, NH₃-N, NO₃-N, NO₂-N and the phytoplankton gross in the purifying area were higher than that in the breeding area by 5.44 times, 1.35 times, 4.03 times, 2.55 times and 12.77 times, respectively. On the contrary, the data of the purifying area were lower than that of the breeding area by 122%, 146 %, 144%, 412% and 417%, respectively in 2009 with the system. In 2009, the economic aquatic plants absorbed the nutrient elements: N 0.208 8 kg, P 0.267 3 kg, K 0.022 5 kg in water and the filter-feeding fish and shellfish took 2 229.5 kg fish (shellfish) nutrients. The variation coefficient in the system of Alk, PO₄-P, NH₃-N, NO₃-N, NO₂-N and phytoplankton gross decreased by 8.43%, 26.98%, 62.33%, 17.01%, 0.01%, 35.55%, respectively compared with 2008.

Key words: artificial biological purification system, nutrient, the stability of water quality