Carbon removal from the atmosphere is needed to keep global mean temperature increases below 2 °C. Here, we develop a model to explore how alkalinity production through enhanced iron sulfide formation in low-oxygen aquatic environments, such as aquaculture systems, could offer a cost-effective means of CO₂ removal. We show that enhanced sulfide burial through the supply of reactive iron to surface sediments may be able to capture up to a hundred million tonnes of CO₂ per year, particularly in countries with the highest number of fish farms, such as China and Indonesia. These efforts could largely offset the carbon footprint associated with their aquaculture industry. Enhanced sulfide burial could directly benefit both fish farms and surrounding ecosystems by removing toxic sulfide from aquatic systems, providing an addition to durable global CO₂ removal markets and a path towards large-scale, carbon-neutral aquatic food production.