Cutting marine content in feed 'has made aquaculture impact worse'
Researchers say substitution of wild fish for soy protein and rapeseed oil in farmed fish diets pushed up greenhouse gas emissions, land use, and water consumption
A new study has shown the dramatic impact that changes in aquafeed composition have had on the environmental footprint of European aquaculture over the past two decades, despite a significant drop in the use of wild fish as feed.
The research was led by Björn Kok and Dr Wesley Malcorps, both of Stirling University’s Institute of Aquaculture. They found that lower inclusion of fishmeal and fish oil in aquafeed has dramatically reduced dependence on marine resources. However, it has also shown that the shift away from marine ingredients has had significant unintended consequences on the environmental footprint of European aquaculture.
Between 2000 and 2020, the European aquaculture industry reduced its overall use of wild‑caught fish as feed by 13%, even as the sector nearly doubled in size - largely driven by the expansion of Atlantic salmon farming in Norway.
However, the new study suggests a substantial increase in overall impact was observed across several key environmental indicators: greenhouse gas emissions rose by 314%, land use by 594% and water consumption by 236%. Marine eutrophication, the build-up of excess nutrients that trigger harmful algal growth in water, also showed a significant rise of 630%, and freshwater eutrophication increased by 468%.
Identifying the drivers
The pioneering study used Index Decomposition Analysis, a technique capable of separating the effect of different drivers such as sector growth and efficiency gains to the impact of individual ingredients within specific sub-sectors. This approach delivered what the IoA said is an unprecedented breakdown of what is driving change across the entire European aquaculture industry.
By isolating the contributions of production growth, efficiency improvements, and shifts in feed ingredients, the research team now hopes that their work will support more informed and sustainable decision making across the aquaculture industry.
The study shows that, as marine ingredients have been replaced with plant-based ingredients, the environmental footprint of feed use has grown, mainly due to inclusion of soy protein concentrate and rapeseed oil, which have disproportionately high environmental impacts.
Other factors, such as the proportion of species farmed in Europe and how efficiently fish convert feed into growth, were shown to have made almost no difference to any of the environmental impacts.
If environmental sustainability assessments focus on a single headline metric, they risk telling an incomplete, and sometimes misleading, story
In their study, the researchers found that although wild fish use dropped by 59% per kilogram of fish farmed in Europe, this was offset by a substantial increase in greenhouse gas emissions (+103%), land use (+336%) and water consumption (+65%). Marine eutrophication showed a significant rise of 285%, as did freshwater eutrophication which increased by 167%. When the model is scaled up, it illustrates the potential impact on a European-wide scale.
Misleading metric
Study lead author Björn Kok, a PhD student at Stirling and technical lead in sustainability metrics for aquafeed producer Skretting, said: “Reducing dependence on marine resources has been treated as the main environmental sustainability goal in aquaculture. However, if environmental sustainability assessments focus on a single headline metric, they risk telling an incomplete, and sometimes misleading, story. We need a comprehensive view on environmental sustainability.”
Study co-lead, Dr Wesley Malcorps, a research fellow at the IoA, said: “We need to make better use of what we already have, such as fish processing by-products, which are rich in nutrients and have a low environmental footprint.
“Novel ingredients (Editor's note: insect meal, single cell proteins, etc) show potential to support long term industry growth, but they still face challenges around inconsistent quality, limited supply, and high costs. At their current stage of development and scale, they have yet to deliver the environmental sustainability performance many expected.”
The study was led by the University of Stirling, alongside partners Blue Food Performance Ltd, University of Zurich, and Utrecht University.
Sustainable aquafeed? The devil is in the detail is published in the Journal of Cleaner Production.
