Off the coast of Senegal, where large Chinese ships now catch as much fish in a week as Senegalese fishing boats can catch in a year, the population of mackerel and sardines is dwindling . In Peru, home to the world’s largest fishery of a small fish called anchoveta–once fished with no restrictions–the government has spent the last several years retraining 2,000 fishermen in new jobs to help curb overfishing. In the U.S., the West Coast sardine fishery was closed in 2017 for the third year in a row because of a crash in sardines.

Each fishery provides at least a portion of its catch to be made into fishmeal, small pellets of protein and nutrients that are used as food for livestock and fish farms. If demand for seafood for humans is growing quickly, so is demand for fish fed to other fish. Aquaculture production has more than doubled since 2000. Recognizing that the ocean can’t keep up, one startup is working on making fish feed from another source: carbon dioxide.

“We can take untreated flue gas from various industrial emissions . . . and just pipe it into our plant, rather than putting it in the atmosphere,” says David Tze, CEO of NovoNutrients, which is currently scaling up a system that it has proven works in a lab.

The startup’s process uses carbon dioxide, along with other emissions, to feed microbes that can then become protein for companies that make pellets of food for fish. Those microbes are similar to ones that evolved to live near gas vents in the ocean; the startup arranges them with other species into “microbial factories” that work together to make the whole process more efficient.

The company is also developing new microbes, using synthetic biology, that can produce particular nutrients–vitamins or probiotics, for example–that can also be used as ingredients in feed. All of this will happen in pipes that help the gases dissolve in water, rather than in the large tanks that are used for fermentation in a brewery or some pharmaceutical companies. The pipes can connect directly to a cement plant or other industrial emitter and then into a fishmeal factory next door. Hydrogen, which can be produced through electrolysis of water using solar power, can provide energy for the system.

For NovoNutrients, it’s a way to turn a waste product and a major greenhouse gas into something of value. “About 36 billion tons [of CO2] a year are emitted globally, and we are not aware of other economically feasible large-scale carbon utilization practices,” says Tze. “We’re sure others will emerge over time, but we think it will be interesting to be in that first batch to be commercialized.”

Because carbon dioxide emissions are often free, and some companies will even pay to have the gas captured, the process is also cheaper than catching fish to turn into fishmeal. The demand from aquaculture has made fishmeal valuable, and producing nutrients through the process is even more valuable; protein meal might sell for around $1,000 a ton, but nutrients like probiotics can sell for $1,000,000 a ton.