Abstract: A model of water circulating pond aquaculture system for fish rearing was constructed and tested, including water source, fish pond, eco-canal (first-level purification), second-level purification pond and third-level purification pond, and its effect of removing nitrogen and phosphorous was studied. The test-running of the model from May to October 2010 showed that after three levels of purification, the concentration of ammonia nitrogen in outflowing wastewater from the system was maintained around 0.33 mg•L^-1 and even lowered down to 0.010 3 mg•L^-1 in June, and the concentration of nitrite nitrogen was kept lower than 0.02 mg•L^-1, making the concentration of total nitrogen meet the criteria of Grade V of the Standard for Surface Water Environment Quality (GB 3838－2002), and the concentration of total phosphorous the criteria of Grade III of the Standard for Surface Water Environment Quality. The effect of the model removing chlorophyll-a was also very obvious, ranging from 16.10% to 91.22% in rate. It is clear that the model could remove surplus ammonia nitrogen, nitrite nitrogen, total nitrogen, total phosphorous and chlorophyll-a from the wastewater. But, in this experiment, the purification ponds did not show their function of effect multiplier level by level, maybe due to the excessive density of aquatic plants as a result of poor management, which led to fluctuation of water quality. The test in the past two years demonstrates that the model of water circulating pond aquaculture system is still in the process of improving functionally, but has not yet got mature.

Key words: Water circulating aquaculture, nitrogen, phosphorous, removal