Introduction
Aquatic animals provide essential and unique nutrients vital to human health and are produced along a continuum of capture fisheries and aquaculture rather than a simple dichotomy. As fisheries and aquaculture supply chains become under increasing pressures, maximising nutrient output for human consumption is increasingly critical. Marine ingredients, primarily fishmeal and fish oil, have long supported aquaculture production and provided omega���3 fatty acids to consumers, but their use has faced increasing sustainability concerns. Metrics such as the Forage Fish Dependency Ratio (FFDR) and Fish In: Fish Out (FIFO) ratios have been used to assess the use of "fish as feed," yet they largely overlook nutrient retention from reduction fisheries to final aquaculture products. They also inadequately capture broader food���system dynamics, including market demand, co���product multifunctionality, and the growing use of fish by���product ingredients. Earlier FIFO approaches were not compatible with Life Cycle Assessment (LCA), while later economic allocation (eFIFO) methods improved compatibility but still failed to address nutrient retention. The economic nutrient FIFO (neFIFO) was developed to quantify marine nutrient retention within aquaculture systems. This paper synthesises evidence on marine ingredient sourcing, evaluates fish���conversion and nutrient���retention metrics, and presents species���specific case studies comparing the various FIFO approaches using a FIFO Performance Tool to support PEFCR compliant LCAs.
Summary of main findings
This section highlights the most important findings of this study, showing challenges and opportunities and where meaningful improvements can be made. These insights point directly to the most effective pathways for advancing progress, towards key Sustainable Developments Goals, and re-balancing access to healthy, nutritious seafood globally.
Aquatic foods are important for human nutrition and come from a continuum of aquaculture and fisheries. Therefore, it is crucial to maximise nutrient availability for people across the whole system, not treat them as separate silos.
Widely used fish dependency indicators like Forage Fish Dependency Ratio (FFDR) and traditional fish efficiency indicators such as Fish In: Fish Out (FIFO) are too narrow and do not consider food system dynamics such as:
- market demand and competition for fishery resources.
- multiple end uses of marine ingredients.
- the increasing role of fish by-products in marine ingredient supply.
FFDR and the traditional FIFO are also not compatible with LCA frameworks, they cannot be easily compared with other impact metrics such as Global Warming Potential, limiting their integration in broader sustainability assessment.
To consider food system dynamics as outlined in point 2, economically allocated eFIFO offers a more realistic approach considering:
- treats relative economic value as a proxy for nutritional value and utilisation strategies.
- assigns higher impacts to limiting feed components (e.g. fish oil).
- attributes lower footprints to by-products, thereby incentivising their use in aquafeeds.
While eFIFO was a significant step forward, it still failed to consider the nutritional content of farmed or feed fish that is a major reason for their inclusion, particularly in regard to critical Long Chain n-3 Fatty Acids (LC n3 FAs).
The need for a robust and standardised metric to improve the retention of fishery���derived nutrients (e.g., EPA+DHA) in aquaculture has led to the development of the nutrient Fish In: Fish Out (nFIFO) metric. This approach, particularly the economically allocated neFIFO, could help to upcycle hitherto unavailable EPA DHA sources for human consumption
An access link to the FIFO Performance Tool is provided, enabling stakeholders to calculate the different versions of FFDR and FIFO described, to compare with LCA metrics and align with industry standards. This empowers stakeholders to directly apply their own data, integrate the results into broader sustainability assessments, and better evaluate the efficiency and resource implications of different feed strategies (e.g., FCR improvements, higher by-product inclusions, and co-product economic value changes).
Nutrient efficiency is not enough on its own: even if nutrient retention is improved, it does not automatically ensure affordability or access. Nutrition-sensitive strategies are required to guarantee equitable access to key nutrients without overusing environmental resources.
Effective fishery management must extend beyond stock status alone to include ecosystem���level assessments and consideration of broader impacts on ecology.
Acknowledgment
We would like to thank Dr. Wenbo Zhang (College of Fisheries and Life Science, Shanghai Ocean University) for providing published papers on Chinese tilapia production systems.