Impact of rice-crab and rice-fish co-cultures on the methane emission and its transport in aquaculture ponds

Aquaculture ponds are as hotspots for methane (CH₄) emissions of increased worldwide interest. However, management strategies and underlying mechanisms to mitigate CH₄ emissions from aquaculture ponds remain little explored. In this study, we constructed new rice-crab and rice-fish co-culture systems by planting rice in crab and fish ponds and conducted a 2-year field experiment to examine the effect of co-culture on CH₄ emissions and transport pathways. The results showed that compared with crab and fish monoculture, co-culturing with rice significantly reduced CH₄ emissions by 23.1 % and 23.7 % for crab and fish ponds over 2 years, respectively. Further analysis clarified that the mitigating effect of co-culturing with rice on CH₄ emissions resulted from the reduction of CH₄ ebullition from the stocking ditch, but not from the feeding platform. The effect of co-culturing with rice on CH₄ transport varied by functional areas. No significant effect of co-culture was found on diffusive CH₄ emission neither in the stocking ditch nor on the feeding platform. On the feeding platform, co-culture increased additional rice-mediated CH₄ emissions while it mitigated CH₄ ebullition under the combined effect of planting rice on CH₄ production and oxidation. In the stocking ditch, co-culture significantly reduced CH₄ ebullition by reducing sediment depth. Furthermore, co-culture obtained additional rice yields, leading to lower yield-scaled CH₄ and higher economic effects. These findings highlight that co-culturing with rice is a valuable solution for sustainable aquaculture development by reducing CH₄ emissions while increasing food production.