Nutrient dynamics and balance of zero–water exchange ponds of grass carp, crucian carp and bighead carp

This study aimed to investigate the nutrient dynamics and balance of zero–water exchange ponds of grass carp Ctenopharyngodon idella, crucian carp Carassius auratus and bighead carp Aristichthys nobilis, and explain advantages of the zero–water exchange mode from the perspective of material flow. This study was conducted for two years. The polyculture ponds of grass carp, crucian carp and bighead carp were grouped into the treatment group using the zero–water exchange mode, while the ordinary polyculture ponds of grass carp, bighead carp, and crucian carp were grouped into the control group. The results showed that 1) the treatment group reduced water conductivity, dissolved solids and sediment organic carbon significantly (P < 0.05), and improved water transparency significantly (P < 0.05); 2) the carbon, nitrogen, and phosphorus accumulation amount and rate in the water of the treatment group were significantly lower (P < 0.05) than those in the control group, so was the sediment accumulation rate of organic carbon and nitrogen (P < 0.05); 3) the carbon, nitrogen, and phosphorus utilization efficiency of stocked fish in the treatment group were significantly higher (P < 0.05) than those in the control group, with an increase of 29.49%, 21.72%, and 20.65%, respectively. Therefore, the zero–water exchange pond was a green and efficient aquaculture mode, which could improve water quality, reduce nutrient accumulation, and improve the utilization efficiency of nutrients effectively. Considering the nutrient emissions from aquaculture in China, the zero–water exchange mode has a good value for promotion.