Aquaculture Feed Sustainability Trade-Offs

For years, the sustainability of aquaculture feeds has largely been framed around one simple question: how much fishmeal and fish oil are we still using? Reducing dependence on wild-caught fish has become the symbolic benchmark — the headline metric, the figure most often quoted.

However, research led by Björn Kok and Wesley Malcorps of the Institute of Aquaculture at the University of Stirling challenges this widespread equation. Cutting marine ingredients in feed can indeed reduce pressure on ocean resources, but it does not automatically make aquaculture more sustainable overall. In Europe, the gradual phase-out of fishmeal and fish oil has brought significant environmental trade-offs.

Between 2000 and 2020, European aquaculture reduced its total use of wild fish in feed by 13%, despite the sector nearly doubling in size. Much of this expansion was driven by Atlantic salmon farming, particularly in Norway.

The critical point is that, during the same period, several key environmental indicators increased sharply

Greenhouse gas emissions rose by 314%, land use by 594%, and freshwater consumption by 236%. Even more striking were eutrophication impacts — the nutrient accumulation that fuels algal blooms and ecosystem imbalances — with marine eutrophication up 630% and freshwater eutrophication up 468%.

To interpret these results correctly, an important clarification is needed: this is not about “grading” aquaculture or arguing that reducing wild fish inputs is a mistake. Rather, the study highlights the risks of evaluating sustainability through a single metric. Environmental impacts do not disappear — they often shift.

The study applies a method known as Index Decomposition Analysis, which separates the influence of different factors. It isolates what is driven by sector growth, what results from efficiency improvements, and what stems from changes in feed composition. This methodological step is crucial, as it avoids conflating distinct drivers and allows for a clearer understanding of what is truly shaping aquaculture’s environmental footprint.

One of the most uncomfortable findings concerns substitute ingredients. According to the analysis, replacing marine ingredients with plant-based alternatives has increased feed-related environmental impacts — particularly due to two widely used components: soy protein concentrate and rapeseed oil. In the model, these ingredients show a disproportionately high environmental burden relative to their inclusion rates, helping explain why some indicators rise even as reliance on wild fish declines.

By contrast, other factors often highlighted in public debate — such as the mix of farmed species in Europe or improvements in feed conversion efficiency — played little or no role in explaining the overall impact differences during the period examined.

The picture becomes even clearer when examining impacts per kilogram of farmed fish

Over twenty years, wild fish use per kilogram dropped by 59%. Yet per kilogram emissions rose by 103%, land use by 336%, and freshwater consumption by 65%. Eutrophication also increased significantly: +285% in marine systems and +167% in freshwater environments.

In simple terms: dependence on marine resources has declined. But the trade-off has been a heavier footprint elsewhere — particularly on land, where crop production, industrial processing, land occupation, and supply chains come into play.

This leads to one of the study’s most concrete recommendations. To genuinely improve overall sustainability balance, researchers point to an underutilized asset already available: fish processing by-products. These are nutrient-rich, carry relatively low environmental impact because they originate from existing value chains, and may represent a more robust solution than an automatic shift toward high-footprint plant ingredients.

In the background remain so-called novel alternative ingredients, often presented as the next breakthrough. The potential is real, but the research stresses that they still face practical constraints: inconsistent quality, limited availability, and high costs. At their current scale and level of development, they are not yet delivering the comprehensive environmental performance many had assumed.

The ultimate lesson is both simple and demanding: reducing wild fish use in aquaculture feeds is an important step, but it cannot be the sole benchmark. Focusing on a single parameter risks telling an incomplete — and sometimes misleading — story. True sustainability, the kind that endures across industrial decisions and long-term strategies, is built on measured trade-offs and attention to detail. And in aquaculture feeds, as is often the case, that is precisely where the direction is decided.