This article, written by Dr Brett Glencross, was first published in International Aquafeed, May 2026 edition

A recently published study by the University of Stirling titled "Sustainable aquafeed? The devil is in the detail", provides a sobering reality check for the global aquaculture industry. For decades, the narrative of "sustainable seafood" has been anchored to a single, intuitive metric: reducing our reliance on wild-caught fish to feed farmed fish. On the surface, we have been making significant inroads to that goal. But as this recent study reveals, our obsession with "Fish-In: Fish-Out" (FIFO) and Forage Fish Dependency ratios (FFDR) ratios has blinded us to a much larger environmental crisis brewing on land.

For the best part of thirty years, the aquaculture industry has been criticised for the "vacuuming of our oceans to feed the insatiable appetite of farmed salmon, shrimp, and marine fish”. In response, scientists and feed manufacturers embarked on a quest to replace fishmeal and fish oil with (mostly) plant-based alternatives. We were told that by swapping anchovies for soy and sardines for rapeseed, we were "relieving pressure on marine ecosystems”. It was a simple, straightforward, and catchy narrative. It was also, as study reveals, dangerously simplistic.

The study analysed European aquaculture between 2000 and 2020, and it confirmed that we have indeed succeeded in reducing the marine ingredient contents in our feeds. Per kilogram of farmed fish, our use of wild-caught fish dropped by a staggering 59%. In absolute numbers, the European industry uses 13% wild-fish in 2020 than it did in 2000. If that were the only number on the score card, we’d be popping the champagne, giving a pat on the back to all those fish nutritionists working on that issue and issuing a “job well done”.

However, during that same period, while we were busy saving forage fish, the greenhouse gas emissions associated with feed rose by 314%. Land use skyrocketed by nearly 600%. Freshwater consumption more than doubled, and the nutrient runoff—marine and freshwater eutrophication—surged by over 400% and 600%, respectively. We haven't actually reduced the footprint of aquaculture; we have simply “onshored” it from the blue parts of the map to the green ones. And as we’ve discussed other recent columns, that just exacerbates the biodiversity impacts.

An important element of the Stirling study was its use of the "Index Decomposition Analysis" to isolate those drivers of change. This proved that the shift in feed ingredients was the dominant factor in driving up environmental impacts. It was a factor that far outweighed the effects of sector growth or changes in farming efficiency. Our problem here though is that we simply cannot do without the terrestrial crops, specifically soybean, corn, wheat and rapeseed. Each of these ingredients carry a heavy ecological price tag that often exceeds the marine ingredients they replace. But they bring scale, supply and affordability to the equation. There is nothing else that comes close in their supply potential. We just need to balance the impacts better. When we feed a salmon soy grown on converted land in South America, we aren't just feeding it protein; we are feeding it the carbon debt of deforestation, the chemical load of intensive pesticides, and the huge water footprint of an industrial monoculture.

Perhaps another key revelation was that our technical gains in "Feed Conversion Ratios" (FCR have done almost nothing to offset the damage. We have become incredibly good at growing fish faster and with less total feed, but because the “ingredient choice” used in that feed has become so much more environmentally "expensive”, those efficiency gains are becoming harder to swallow.

The takeaway here isn't that we should return to overfishing the oceans to make more fishmeal. That is not a viable path. The takeaway is that we must stop worshiping at the altar of the FIFO ratio.  As the authors of the study argue, focusing on a single headline metric like "dependence on marine resources" risks telling a misleading story. True sustainability requires a "multi-criteria" approach. We cannot claim to be cleaning up an industry if we are trading a localized impact on fish stocks for a global impact on the climate and a regional impact on South American biodiversity.

So, where do we go from here? The researchers point toward a future that looks less like an industrial conveyor belt and more like a circular economy. First, we must stop ignoring the "gold" in our own backyard: fish processing by-products. Currently, massive amounts of heads, frames, and guts from the seafood we eat are discarded or underutilized. These resources are nutrient-dense, require no new land or water to produce, and have a negligible environmental footprint. Utilizing these is a "no-brainer" that the industry needs to continue to scale. Globally we are currently using about 2.4 million tonnes of fishmeal and fish oil each year from these resources (about 40% of global production), but we need to do better.

As the title of the study says, “The devil is in the detail.” For the consumer, this means being sceptical of sustainability labels that only tell part of the story. A "100% veg-fed" salmon might sound like a victory for the oceans, but it might be a disaster for the Brazilian rainforest. For industry and policymakers, it means it is time for a radical rethink and improved transparency on how we assess impacts. We need feed formulations that are optimised not just for growth and fish health, but also for a "Global Warming Potential" and "Land Use" budget (among others). We have spent thirty years trying to get the "fish" out of our farmed fish; we may spend the next thirty realising that that “Fish-Free” isn't necessarily our greenest option.