Study Reveals Comprehensive Picture of Greenhouse Gas Emissions from Aquaculture

Aquaculture's 'Carbon Ledger' Systematically Clarified for the First Time

While global attention has been focused on carbon emissions from livestock, another massive food production system — aquaculture — has long lacked systematic understanding of its greenhouse gas emissions. A recent study published in Frontiers of Agricultural Science and Engineering has, for the first time, conducted a comprehensive review of greenhouse gas emissions across the entire aquaculture value chain, revealing a complex and highly differentiated emissions landscape.

The study found that greenhouse gas emissions from aquaculture do not stem from a single source but are jointly driven by four key components: feed production, energy consumption during the farming process, biochemical processes in ponds or water bodies (including the release of methane and nitrous oxide), and land-use change and infrastructure development. This finding provides a crucial scientific basis for targeted emission reduction.

Feed Production: The Largest 'Hidden Emission Source'

The study points out that in most fed aquaculture systems, feed production is the single largest source of emissions. Research conducted in China shows that greenhouse gas emissions from feed production account for as much as 52% of total emissions. This means that the carbon footprint of the entire feed supply chain — from fishmeal processing to soybean cultivation, from raw material transportation to feed manufacturing — far exceeds common expectations.

Animal-based ingredients in feed, such as fishmeal and fish oil, require extensive fishing and processing, while the cultivation of plant-based ingredients like soybeans involves land-use change and fertilizer application — all of which generate substantial greenhouse gases. For intensively farmed carnivorous fish species, higher feed conversion ratios further amplify this problem.

Methane Emissions: The 'Carbon Bomb' of Freshwater Ponds

Even more noteworthy is that in regions where freshwater pond farming predominates, such as China, methane emissions from aquaculture water bodies are particularly alarming. Research data shows that methane contributes approximately 90% of greenhouse gas emissions from these farming systems, making it a veritable 'carbon bomb' in freshwater aquaculture.

The mechanism behind this phenomenon is straightforward: residual feed and feces that accumulate at the bottom of ponds undergo anaerobic decomposition under oxygen-depleted conditions, producing large quantities of methane gas. Since methane has a greenhouse effect roughly 28 times that of carbon dioxide, even relatively modest emission volumes translate into enormous impacts when converted to carbon equivalents. This finding carries profound policy implications for China, which operates the world's largest freshwater aquaculture sector.

Significant Species Differences: A Spectrum from 'Carbon Sink' to 'Carbon Source'

One of the most striking findings of the study is the vast disparity in emissions among different aquaculture species, forming a complete spectrum from 'carbon sink' to 'carbon source.'

Low-emission or even negative-emission species: Bivalve shellfish (such as oysters and clams) and seaweed farming, which do not rely on feed inputs, produce extremely low or even negative greenhouse gas emissions. These forms of aquaculture not only require no feed but can actually sequester carbon through photosynthesis and calcium carbonate deposition, functioning as 'carbon sinks.' This means that reasonably expanding the scale of shellfish and seaweed farming could not only provide high-quality protein but also serve as an important pathway for ocean carbon sequestration.

Medium-emission species: Herbivorous or omnivorous fish (such as carp and tilapia) produce relatively low emissions under moderate farming intensity. These species have higher feed conversion efficiency and a larger proportion of plant-based ingredients in their feed, keeping the overall carbon footprint manageable.

High-emission species: Intensively farmed carnivorous fish (such as salmon and trout) and shrimp exhibit significantly higher carbon emission intensity due to their rigid demand for high-protein feed and continuous energy supply. The study notes that some high-intensity farming models produce carbon emissions comparable to terrestrial livestock operations, challenging the widespread assumption that 'seafood is always more environmentally friendly than meat.'

Emission Reduction Pathways and Future Outlook

This study provides clear directional guidance for the green transformation of the aquaculture industry. In the short term, optimizing feed formulations, improving feed conversion rates, and reducing feed waste are the most direct and effective measures for lowering emissions. In the medium to long term, improving pond management techniques to reduce anaerobic fermentation in bottom sediments, promoting aeration equipment, and developing recirculating aquaculture systems all hold promise for substantially cutting methane emissions.

At the industrial structure level, moderately expanding the share of low-carbon or even carbon-negative species such as shellfish and seaweed, and optimizing the mix of farmed species, may be key strategies for achieving industry-wide carbon neutrality. At the same time, incorporating carbon emission metrics into seafood evaluation systems and establishing 'carbon labeling' programs could help guide consumers toward more environmentally friendly choices.

As global attention to food system carbon emissions continues to intensify, the importance of emission reduction in aquaculture — the fastest-growing source of animal protein — will become increasingly prominent. The value of this study lies not only in quantifying the scale of the problem but also in pointing the way toward solutions: the future of aquaculture should not merely pursue production growth but must also strive for alignment with climate goals.