Abstract
The budget of nitrogen and phosphorus in polyculture systems of snakehead (Channa arguss) and bighead carp (Hypothalmichthys nobilis) was studied with land-based enclosures from August 1 to November 28, 2014. Four treatments were designed, including monoculture of snakehead (C) and polyculture of snakehead with bighead carp (CH1, CH2 and CH3). Snakehead were stocked in all enclosures at 9.00ind/m2. Bighead carp was stocked in three different densities, i.e., 0.12 (CH1), 0.15 (CH2) and 0.18 (CH3)ind/m2. Results showed that all the three polyculture systems showed the higher yield of cultured animals than the monoculture system (P<0.05). The survival rate of snakehead in C system showed the lowest value (P<0.05), while no significant difference was found in the final body weight and yield of snakehead among different systems (P>0.05). The survival rate of bighead carp in CH1, CH2 and CH3 systems were all 100.00%, while the final body weight and yield in the CH3 system showed the lowest value (P<0.05). Feed was the main input of nitrogen (97.89%–98.21%) and phosphorus (99.37%–99.53%) in all systems. The main part of output of nitrogen and phosphorus was sediment accumulation, which accounted for 52.68%–67.31% and 84.33%–86.27% of the total output, respectively. The sediment accumulation of nitrogen in the C system showed the highest value (P<0.05), while no significant difference was found in the sediment accumulation of phosphorus among different systems (P>0.05). The utilization efficiency of nitrogen of CH2 system was significantly higher than that of C system (P<0.05), while no significant difference was found in the utilization efficiency of phosphorus among all the four systems (P>0.05). In conclusion, the optimum stocking density for the polyculture systems in this study was snakehead at 9.00ind/m2 and bighead carp 0.15ind/m2, which exhibited better ecological efficiency and economic benefit.
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