Effects of pond-paddy field aquaponics on water quality and growth of Macrobrachium rosenbergii

In order to develop a new pond farming model with characteristics of energy saving and emission reduction, a Macrobrachium rosenbergii pond-paddy field aquaponics experiment was carried out. The dynamics of major water environment factors and the shrimp growth were monitored in a trial pond (combined with paddy field) and the control pond (M. rosenbergii monoculture). The effects of this new farming model on the water quality and growth of M. rosenbergii were analyzed. The trial pond was transformed into two parts (aquaculture area and paddy field), and each part amounted 50% of the area. The rice was planted on April 22, 2018, and the shrimps were seeded on May 12. Sampling and monitoring began on June 28. The results show that: 1) The average water temperature of the trial pond was 0.82 °C lower than that of the control pond. 2) The concentrations and variation coefficients of ammonium nitrogen (NH₄ ⁺-N), nitrate nitrogen (NO₃ ⁻-N), nitrite nitrogen (NO₂ ⁻-N), active phosphate phosphorus (PO₄ ³⁻-P), total particulate matter (TPM), particulate organic matter (POM), particulate inorganic matter (PIM) and chemical oxygen demand (COD) in the trial pond were all lower than those in the control pond with significant difference (P<0.05). The values of these water quality parameters in the control pond showed instant increase with high amplitude at the later stage of the trial period. 3) The specific growth rate and relative growth rate of M. rosenbergii body mass in the trial pond were 3.07%·d⁻¹ and 459.40%, respectively, while those in the control pond were 2.86%·d⁻¹ and 397.44%, respectively. The results indicate that shrimp pond-paddy field aquaponics can reduce the pond water temperature in summer, reduce the nutrient concentrations and chemical oxygen demand significantly, maintain water quality stable, and promote better growth of M. rosenbergii.