Better assessments of greenhouse gas emissions from global fish ponds needed to adequately evaluate aquaculture footprint

While providing protein for a fast-growing human population, the ongoing boom in global aquaculture comes with environmental costs. Particularly, the intense greenhouse gas (GHG) emissions reported for several aquaculture systems are a source of concern. Still, we argue that actual emissions could be multiple times higher than currently thought. Most studies supporting existing estimates solely rely on measurements of water-atmosphere diffusive fluxes of GHG, whereas methane (CH4) and nitrous oxide (N2O) emissions during drainage and refilling and CH4 bubbles emerging from sediments are largely ignored. Yet, abundant evidence for similar aquatic ecosystems suggests that these largely unaccounted emission pathways may be responsible for a large share of annual GHG emissions. Uncertainties from overlooking important emission pathways may have serious consequences, including incorrect advice on mitigation strategies and overly optimistic assessments of the GHG footprint of cultured freshwater fish. To ensure a low-carbon future for global aquaculture, we contend that GHG assessments in fish-farming ponds must extend beyond the focus on diffusive water-atmosphere fluxes and include all emission pathways and possible carbon burial in the sediment. In parallel, we call for a better understanding of the biological, microbiological and physical drivers of aquaculture emissions to effectively support mitigation strategies to minimize the footprint of this nutritionally valuable protein source. (C) 2020 Elsevier B.V. All rights reserved