The aquaculture industry faces criticism for its reliance on wild fish for feed, particularly for the production of fishmeal and fish oil, which are essential components of aquafeeds.
To address these concerns, researchers from the Institute of Aquaculture at the University of Stirling, Blue Food Performance Ltd, Lancaster University, the University of Aberdeen, and the University of Cambridge have developed a new method to analyze the retention of omega-3 and other nutrients from marine ingredients, such as fishmeal and fish oil, used in aquafeeds for farmed fish.
Marine ingredients are vital for the transfer of nutrients, particularly omega-3 fatty acids, to farmed fish and the humans who consume them. However, they are often criticized for their dependence on finite resources and the practice of “feeding fish to fish.” This new method will help the aquaculture industry become more efficient in retaining valuable nutrition from these limited ingredients.
Existing and widely used fish-in/fish-out (FIFO) metrics measure the biomass of wild fish used to produce farmed fish but do not account for the retention of essential nutrients, such as omega-3 long-chain polyunsaturated fatty acids (LC-PUFA), from feed to the final farmed product. This oversight has led to calls for a more nuanced approach to assessing the efficiency of aquaculture systems.
Introducing the nFIFO ratio
The nFIFO ratio is a new tool designed to measure the flow of nutrients, particularly omega-3 LC-PUFA, from marine resources to farmed fish. Unlike traditional FIFO metrics, nFIFO focuses on nutrient retention, providing a more comprehensive understanding of how efficiently aquaculture systems convert wild fish into nutrient-rich farmed fish.
In a recent study published in Aquaculture, researchers quantified the retention of omega-3 LC-PUFA from feed to farmed salmon. They found that, on average, only 37.4% of the omega-3 PUFA in feed was retained in farmed salmon, resulting in an nFIFO ratio of 2.17. This means that more than twice the amount of omega-3 LC-PUFA from wild fish is required to produce the same amount in farmed salmon.
Dr. Richard Newton, Professor of Resilient Food Systems at the Institute of Aquaculture and lead researcher of the study, stated:
“Unlike traditional approaches, this new nFIFO metric accounts for the retention of key nutrients in the final farmed fish, providing a more targeted means to measure and improve resource efficiency in aquaculture. This shift highlights the growing importance of byproducts in transforming marine resources into valuable nutrition within the aquaculture sector.”
Economic allocation and byproducts
The study also applied “economic allocation principles”, commonly used in Life Cycle Assessment (LCA), to account for the value of different components of fish used in feed production. This approach revealed that fish oil carries a higher nFIFO burden than fishmeal, but it also highlighted the benefits of using processing byproducts as raw materials for marine ingredients.
Byproducts, such as trimmings and offal from fish processing, are increasingly used in aquafeeds. These byproducts are highly nutritious and can help reduce waste while providing essential nutrients to farmed fish. The study found that replacing whole-fish-derived meals and oils with byproducts significantly improved the nFIFO ratio, making aquaculture more sustainable and efficient.
Sensitivity analysis: Testing the model
To test the robustness of the nFIFO model, researchers conducted a sensitivity analysis, simulating two scenarios:
- Replacing whole fish with byproducts: In this scenario, fishmeal and fish oil derived from whole fish were incrementally replaced with byproducts. The results showed that using byproducts improved the nFIFO ratio, particularly when replacing high-omega-3 oils such as anchovy oil. This suggests that byproducts can play a key role in improving nutrient retention in aquaculture.
- Increasing fish oil prices: The second scenario examined the impact of rising fish oil prices on the nFIFO ratio. As fish oil prices increased, the nFIFO ratio also increased, reflecting the higher economic value of fish oil and its greater contribution to overall nutrient retention in farmed fish.
Implications for aquaculture sustainability
The introduction of the nFIFO ratio provides a valuable tool for the aquaculture industry to measure and improve nutrient retention, particularly for omega-3 LC-PUFA. By focusing on nutrient flows rather than just biomass, the nFIFO ratio offers a more holistic approach to assessing aquaculture sustainability.
The study also highlights the importance of using processing byproducts in aquafeeds. By maximizing the use of byproducts, the industry can reduce waste, improve nutrient retention, and ease pressure on wild fish stocks. Additionally, the economic allocation approach used in the nFIFO model aligns with broader sustainability goals, encouraging the industry to adopt more circular economy practices.
“Currently, the retention of key omega-3 fatty acids is only about 38%, and we hope to improve that in the future,” said Newton.
“Our approach highlights the importance of promoting better feed management and circular economy principles in aquaculture, allowing the industry to make better use of finite marine resources, reduce waste, drive sustainability improvements, and enhance the nutritional output of farmed fish.”
“The calculation system we have developed can be used as a practical tool for aquaculture stakeholders and policymakers to generate practices that lead to lower environmental impacts while providing high-quality, nutrient-rich farmed fish.”
Conclusion
The nFIFO ratio represents a significant step forward in evaluating the efficiency and sustainability of aquaculture systems. By focusing on nutrient retention, particularly for omega-3 LC-PUFA, nFIFO provides a more accurate and comprehensive metric than traditional FIFO ratios. The study highlights the potential of using processing byproducts to enhance nutrient retention and reduce aquaculture’s environmental impact.
Tools like the nFIFO ratio are essential to ensure that aquaculture can sustainably and efficiently meet global nutritional needs. By adopting these metrics and practices, the aquaculture industry can continue to play a vital role in global food security while minimizing its environmental footprint.
The scientific article includes an Excel file to help stakeholders calculate nFIFO and other FIFO metrics.
Contact
Richard W. Newton
Institute of Aquaculture, Faculty of Natural Science, University of Stirling
Stirling FK9 4LA, UK
Email: richard.newton@stir.ac.uk
Reference (open access)
Newton, R. W., Malcorps, W., Robinson, J. P., Kok, B., Little, D. C., Lofstedt, A., De Roos, B., & Willer, D. F. (2025). Fish as Feed: Using the nutrient Fish In: Fish Out ratio (nFIFO) to enhance nutrient retention in aquaculture. Aquaculture, 602, 742332. https://doi.org/10.1016/j.aquaculture.2025.742332
