Effects of the manure collection equipment on growth performance and nitrogen and phosphorus budgets of Cyprinus carpio var. specularis cage culture in reservoir

Cyprinus carpio var. specularis with body weight of (167.81±34.66) g was reared in a net cage of 5.0 m×5.0 m×2.0 m without (as a control group) and with the manure collection equipment (as a treatment group)at a stocking rate of 40 individuals/m2 at water temperature of 22~32 ℃, pH value of 6.8~7.5 and dissolved oxygen level upon 5.0 mg/L for 90 days to evaluate the input and recycle of nitrogen and phosphorus in the cage water. The results showed that the growth performance in the cage with the manure collection equipment is superior to that in the control cages, and adding the manure collection equipment had no significant effect on survival ratio (P > 0.05). The recycle rate of nitrogen was found to be 76.83% in the cage with the manure collection equipment and 44.14% in the control cage with very significant difference (P < 0.01). The recycle rate of phosphorus was 63.13% in the cage with the manure collection equipment and 35.18% in the control cage with very significant difference (P < 0.01). There were higher utilization efficiencies of nitrogen (28.36%), and phosphorus (21.30%) in the cage with the manure collection equipment than those (25.57% for nitrogen, and 18.25% for phosphorus), with significant difference (P < 0.05). Emissions of nitrogen and phosphorus were reduced to the reservoir water by adding the manure collection equipment to feeding-cage, and the eutrophication effect of cage culture on the environment was decreased.