TN, NH4+-N, NO3−-N, NO2−-N, TP and CODCr concentration of aquacultural drainage river are shown in Fig. 2. It was shown that the average TN concentration of A1 was the highest among three sites, which was 3.0 mg/L. The average TN removal rate was 11.2%. Especially in some days of August, TN concentration was even higher than that in July. The lower TN removal rate might be attributed to large amount of feedstuff added to those ponds.TN concentration decreased to minimum on 21st July, which was 0.9 mg/L.