In January, Farm Forward announced its partnership with the Aquaculture Accountability Project with the release of a new report scrutinizing the sustainability narrative surrounding industrial fish farming, including the widely repeated claim that aquaculture alleviates overfishing. Drawing on recent research, we showed that industrial fish farming relies so heavily on small wild fish—processed into fishmeal and fish oil for feed—that it continues to drive enormous pressure on vulnerable wild fish populations.
Now, new research reveals an even bleaker picture: even where marine ingredients are reduced, aquaculture’s environmental impacts are not shrinking; they are shifting and intensifying.
The study, led by researchers at the University of Stirling and published in the Journal of Cleaner Production, examines how changes in aquafeed ingredients reshaped the environmental impacts of European aquaculture between 2000 and 2020. The authors model how feed composition has evolved over time. As small coastal fish populations have been exploited to or near their limits—and as scrutiny of fishmeal and fish oil dependence has grown—the industry has increasingly turned to land-based crop ingredients to replace marine inputs. The study analyzes what happened as that shift unfolded.
The findings are striking. Over the past two decades, European aquaculture nearly doubled its production. But the environmental impacts linked to fish feed rose even faster. Greenhouse gas emissions from feed production increased by 314 percent. Land use grew by 594 percent. Water use rose by 236 percent. Pollution of rivers, lakes, and coastal waters also climbed sharply, largely because of fertilizer use and nutrient runoff tied to expanding soy and rapeseed farming.
Some of this increase is expected when an industry grows—more production usually means more environmental impact. But the researchers found that the biggest driver was not the growth of aquaculture itself, but changes in the ingredients used to make fish feed.
One way to see this is by looking at the environmental impact per kilogram of fish produced—a measure that accounts for industry growth. Even by that standard, the impacts worsened. Greenhouse gas emissions per kilogram of farmed fish more than doubled, and land use per kilogram increased by 336 percent. In other words, producing each kilogram of farmed fish became significantly more resource-intensive over time, regardless of how much the industry expanded.
The primary drivers were the production of soy protein concentrate and rapeseed oil, ingredients that increasingly replace wild fish in feed formulations. Ultimately, substituting marine ingredients with crops did not reduce environmental impacts. It magnified and transferred them to land.
As Dr. Spencer Roberts of the University of Miami recently observed, “What we’re talking about is not so much increasing efficiency as much as a shift in pressure from ecosystems like the Humboldt Current [in Peru], where the anchovies come from, to ecosystems like the Amazon rainforest where the soy comes from.”
The University of Stirling study uncovers the disturbing reality of the environmental pressures of crop-based feed production. At the same time, like much of the aquaculture literature, it relies on standard feed accounting methods that do not always capture the full scope of marine extraction. As our recent report—drawing on Roberts and colleagues’ 2024 Science Advances analysis—explains, conventional feed accounting often treats trimmings and “by-products” as if they are not wild fish inputs. These materials include heads, frames, offcuts, and even whole non-target fish who are processed into fishmeal and fish oil. As demand for aquaculture feed has grown, these so-called “by-products” have acquired significant economic value. Yet most accounting methods subtract them entirely, making industry feed look less dependent on wild fish than it is. Correcting for these exclusions raised estimated wild fish use by as much as 300% compared to the figure most frequently cited to demonstrate aquaculture’s efficiency.
What the Stirling findings do make clear is that, regardless of accounting method, altering feed ingredients has not lightened aquaculture’s environmental load, but redistributed it. Forest ecosystems, freshwater systems, and agricultural landscapes have absorbed the impacts of expanded crop production, while marine ecosystems still remain under strain.
As researchers revisit the environmental consequences of aquaculture feed, new work is also drawing attention to its nutritional implications. A separate Harvard-led study published in February estimates that if wild fish currently diverted into aquaculture feed were instead retained within Global South countries from which they were caught, they could meet the nutritional needs of up to 31 million undernourished people. Rather than remaining in local food systems, these fish are funneled into feed for higher-value farmed species destined largely for wealthier markets—a far cry from the industry’s claims of “feeding the world.”
Together, these findings point to the same underlying reality: Whether measured in greenhouse gas emissions, land conversion, nutrient pollution, or lost nutrition, the feed systems underpinning industrial aquaculture deepen environmental and social burdens rather than resolving them. Substituting soy for anchovies does not eliminate pressure; it changes where this pressure is concentrated and who bears it.
This is why incremental ingredient substitutions are not enough. Fish farming remains anchored in resource-intensive feed systems, whether those inputs come from oceans or croplands. As long as production continues to expand, environmental and nutritional trade-offs will continue to multiply.
Reducing the scale of sea animal production—and accelerating a shift toward plant protein with lower greenhouse gas emissions, land use, and nutrient runoff—remains essential if we are serious about protecting both marine and terrestrial ecosystems.
Whether you’re cooking for your family or you work in foodservice or procurement, you can find practical steps and resources for serving more sustainable, ocean-friendly food here. To keep up-to-date on our work on this issue, sign up for Aquaculture Accountability Project’s newsletter.