Saltwater Aquaculture Is More Climate-Friendly than Freshwater Aquaculture

As the aquaculture industry grows, new research finds that seafoods raised in marine waters have a smaller carbon footprint than those raised in fresh water.

The world’s aquaculture industry is booming. And it’s no wonder—overfishing in the open ocean has caused populations of many commercially caught fish to plummet. To keep up with the world’s growing demand for seafood, aquaculture, or the rearing of aquatic plants and animals for food, is the obvious alternative.

According to the 2024 United Nations State of the World Fisheries and Aquaculture report, the amount of seafood produced in 2022 from aquaculture exceeded the amount produced from capture fisheries. Within aquaculture, 38 percent of seafood is raised in marine systems, known as mariculture, and the other 62 percent comes from land-based, mostly freshwater systems. Despite aquaculture’s prevalence, the environmental impacts of this industry are still murky.

“To date, climate assessments have not accurately quantified the climate impacts of mariculture, especially with respect to the direct methane and nitrous oxide emissions from aquatic environments,” says Lu Shen, an environmental scientist at Peking University in China.

In a new study, Shen and his colleagues evaluate how marine aquaculture affects the climate, taking into account greenhouse gas emissions from the breakdown of fish feed and the energy used to operate fish farms. They found that the carbon footprint of mariculture is 40 to 50 percent lower than that of freshwater aquaculture. The variance mainly comes down to microbes that produce different greenhouse gases in distinct environments.

In most aquaculture systems, fish get more food than they can eat. The leftovers sink to the seafloor along with plankton, fish poop, and other detritus. Then, the naturally occurring microbes that digest this detritus emit huge amounts of nitrous oxide and methane—potent greenhouse gases. Marine systems differ from freshwater ones because they’re so salty.