As highlighted by Emma Bryce in Anthropocene, fish farms may hold surprising potential to help combat climate change. According to a new model published in Nature Food, adding iron to aquaculture operations could capture as much as 100 million metric tons of carbon dioxide annually in countries where fish farming is widespread—enough to offset most of the carbon footprint produced by these operations. Currently, fish farming contributes about 5% to 7% of the emissions associated with agriculture and livestock globally, so this discovery could be a game-changer.
The link between fish farming and climate change hinges on a serious but often overlooked issue: hydrogen sulfide. This toxic gas accumulates when microbes living in low-oxygen zones—like the sediment beneath a fish farm—feed on organic matter. Because industrial fish farms generate ample waste through leftover feed and fish feces, hydrogen sulfide can build up and threaten fish health both on the farm and in the surrounding waters.
Even small amounts of hydrogen sulfide can trigger high mortality rates in fish farms and send damaging ripples through nearby lake and ocean ecosystems. However, as detailed in the Nature Food study, adding iron ore to these systems neutralizes hydrogen sulfide by forming iron sulfide, which then settles into the sediment where it’s no longer harmful to fish. More importantly for climate mitigation, iron sulfide enhances water alkalinity, allowing the water to draw in more carbon dioxide (CO₂) from the atmosphere and store it in the form of bicarbonate and carbonate. These converted forms of CO₂ remain in the water over the long term.
Encouraged by this dual benefit—reducing fish-killing hydrogen sulfide and sequestering greenhouse gases—the researchers modeled what would happen if fish farms around the world were sprinkled with iron ore. Their simulations took into account various environmental conditions, as well as carbon, iron, and sulfur cycling in marine sediments. In aquaculture-intensive nations such as China, they found the technique could lock away up to 100 million tons of CO₂ each year. On a broader scale, when factoring in fish-farming powerhouses like India and Indonesia, iron enrichment might secure between 25 and 140 million metric tons of carbon. Under the right circumstances, they estimate it could offset 50%—and potentially up to 100%—of aquaculture’s existing carbon emissions.
By cutting emissions so dramatically, iron-assisted aquaculture could transform farmed fish into one of the lowest-carbon sources of animal protein on the market. In fact, iron enrichment could bring down the CO₂ cost per gram of fish protein to as little as zero, or up to 20 grams, compared with 240 grams of CO₂ for each gram of beef protein. Meanwhile, controlling hydrogen sulfide means fewer farmed fish succumb to oxygen-starved waters, improving both yield and ecosystem health.
Of course, mining and transporting iron ore carries costs. But according to the researchers, the price of removing carbon this way—between $100 and $300 per ton—lines up with other carbon removal strategies, and may actually be lower than the social cost of carbon. While the study acknowledges the need for field trials to confirm possible environmental impacts, fish farms occupy a uniquely controllable environment; any intervention can be measured and managed more directly than in the open ocean.
Given that global aquaculture is expected to grow by 22%—ultimately supplying more than half of all fish consumed—this potential for carbon capture may expand too. The more fish farming scales up, the greater the opportunity to sequester CO₂ in the hydrogen sulfide that would otherwise escape into the water and harm fish. With proper management, fish farms could move beyond simply reducing environmental harm, instead actively contributing to climate solutions.
According to Mojtaba Fakhraee, the study’s lead author from Yale University, these findings offer a “dual solution: reducing the carbon footprint of aquaculture while also benefiting the environment.” For an industry on track to play an ever-larger role in feeding the world, transforming fish farms into net-zero or even net-negative ventures would mark a significant step forward in our collective effort to rein in greenhouse gas emissions.
Reference
Fakhraee and Planavsky. “Enhanced sulfide burial in low-oxygen aquatic environments could offset the carbon footprint of aquaculture production.” Nature Food. 2024.
