The environmental concern and safety of pond aquaculture has become an important factor restricting the development of freshwater aquaculture in China. Research and development of efficient, ecological, safe and healthy culture technology and showcase has become an important development direction of domestic and foreign fishery production. In line with the ecological engineering of paddy fields, the integrated paddy-pond recirculating ecological system was constructed. In the system, the paddy field acted as the production unit, meanwhile it worked as a water and nutrient recycling purification unit. In this paper, the treatment efficiencies of the wastewater from a fishpond by a paddy field wetland, and rice and fish production potentials were evaluated for two consecutive years. Biolog Eco micro-plate technology was used to compare the metabolic structure and diversity of microbial community in the inflow and outflow of the paddy field wetland. The results showed that under the hydraulic loads of 0.51 and 0.74 m/d, the overall percent removal rates of \rmNH^+_4
-N, TN, TP and CODMn
by the paddy field wetland were 2.94%—33.38%, 12.60%—92.45%, 16.06%—32.36%, 23.34%—48.50% and 15.37%—61.12%, respectively. The content of DO in outflow of the paddy field wetland was significantly increased. Paddy wetland retained nitrogen and phosphorus from pond culture wastewater. Therefore, the pollution discharge coefficient of TN, TP and CODMn
of wastewater from the pond culture decreased by 0.71—3.03, 0.27—0.31 and 4.19—8.81 kg/t, respectively. The carbon source utilization characteristics of microbial communities in the inflow and outflow of the paddy wetland were changed, while the metabolic functional diversity index of microbial communities in the outflow were significantly higher than that in the inflow which was beneficial for the fish pond culture. Fish yield in the pond of the recirculating aquaculture system increased by more than 22%, while the rice yield reached 9239 kg/hm2
in the system. These results probably implied that the rice field exhibited efficient treatment effect and nutrient recycling effect of wastewater from aquaculture pond and the integrated paddy-pond system could provide more food. The new recirculating planting-culture ecosystem integrating rice and fish production system could be regarded as a clean and sustainable food production system from an environmental point of view and be applied in rural areas of China where crop breeding and fish culture coexist.