REFORMULATION OF ATLANTIC SALMON Salmo salar FEEDS USING ALTERNATIVE AND CIRCULAR INGREDIENTS WITHOUT COMPROMISING PERFORMANCE OR PRODUCT QUALITY
Introduction
Sustainable growth of Atlantic salmon aquaculture requires increasing production to meet rising global demand while maintaining the use of marine resources such as fishmeal (FM) and fish oil (FO) within sustainable limits. This requires the development of alternative feed ingredients that support production without increasing reliance on finite marine resources. Emerging alternatives, including microalgae-derived oils, insect-based ingredients, and circular by-products, have been investigated individually; however, their combined use within complete feed formulations at commercial scale remains insufficiently evaluated. The Millennial Salmon project (Research Council of Norway #319987) aimed to develop next-generation aquafeeds integrating these alternative resources and to assess their biological performance and product quality under commercial like farming conditions. The present study represents the final validation stage of the project, in which fully reformulated diets were tested in a pilot-scale sea-cage trial.
Material and Methods
A feeding trial was conducted in 5x5m sea cages from June to October 2025 at Mowi's Field Trials Station (Averøy, Norway). Atlantic salmon were grown from approximately 3kg to 5kg mean body weight. Four experimental diets were tested in quadruplicate sea cages:
Control diet: conventional commercial formulation
Millennial Salmon diet: optimised low-carbon formulation incorporating project-validated alternative ingredients, including insect meal and oil and microalgae-derived DHA-rich oil
Low Marine diet: high reduction of marine-derived ingredients
Circular diet: high inclusion of circular raw materials (poultry by-products, salmon oil, insect meal and oil, microalgae-derived DHA-rich oil)
The diets were formulated to meet the known nutritional requirements of Atlantic salmon and represent distinct sustainability strategies. Growth performance, feed utilization, and apparent digestibility coefficients (ADC) were evaluated alongside whole-body composition and fatty acid profiles. Product quality traits, fish health and welfare indicators, and oxidative status were also assessed, including lipid peroxidation and antioxidant capacity in liver and intestinal tissues. In addition, the carbon footprint (in kg CO2eq. calculated with the IPCC 2021 100-year GWP with land-use change methodology) of the feed concepts per kg feed and per FCR was evaluated using life cycle assessment (LCA) with economic allocation.
Results and Discussion
All alternative diets resulted in comparable growth and production performance, with no significant differences observed in final body weight, specific growth rate (SGR), feed conversion ratio (FCR), or slaughter yield relative to the Control diet. ADC of protein, fat, and energy remained high across treatments, indicating efficient utilization of the alternative and circular raw materials. Dietary lipid composition influenced whole-body fatty acid profiles, reflecting the use of alternative lipid sources. However, these compositional differences were not associated with changes in fillet quality, as no differences were observed in pigmentation or instrumental colour (Minolta measurements), suggesting preservation of key product quality traits under the tested formulations. No adverse effects on fish health or welfare indicators were detected. Fish fed the Millennial Salmon diet exhibited improved fin condition, reduced skin lesion prevalence, and a lower incidence of cataract formation compared to the Control (p < 0.05). Liver lipid peroxidation increased progressively with decreasing inclusion of marine ingredients, with fish fed the Low Marine diet showing significantly higher malondialdehyde (MDA) concentrations than other treatments. These changes were not accompanied by structural alterations in liver tissue, as histological examination (Figure 1) revealed no pathological findings across dietary groups. The observed responses were therefore interpreted as adaptive physiological adjustments. To complement the biological and product quality assessments, the carbon footprint of the feed concepts was evaluated using LCA. The Circular diet exhibited the lowest carbon footprint (kg CO2-eq), both per unit of feed and when expressed relative to FCR. The Control diet showed the highest footprint per kg of feed. When expressed per unit of production (FCR-adjusted), the Low Marine diet exhibited a slightly higher carbon footprint than the Control, reflecting differences in feed efficiency among treatments. /> /> /> />
Figure 1. Representative liver histology of Atlantic salmon fed Control (a), Millennial Salmon (b), Circular (c), and Low Marine (d) diets, showing adaptive metabolic responses.
Figure 1. Representative liver histology of Atlantic salmon fed Control (a), Millennial Salmon (b), Circular (c), and Low Marine (d) diets, showing adaptive metabolic responses.
Conclusions
The present study indicates that the integrated inclusion of microalgae, insect-derived ingredients, and circular by-products can substantially reduce reliance on marine resources in Atlantic salmon feeds without adversely affecting growth performance, welfare indicators, or product quality under the tested conditions. The results further suggest that dietary lipid composition and oxidative stability remain important considerations in the formulation of low-marine feed concepts, particularly in diets enriched with alternative lipid sources. From an environmental perspective, LCA showed that feed formulations incorporating Schizochytrium sp. biomass and insect-derived ingredients may reduce the carbon footprint of salmon feed, depending on formulation strategy and system boundaries. These findings highlight the importance of evaluating environmental performance at the level of complete feed formulations and production efficiency, including FCR, rather than at the ingredient level alone. Further analyses of oxidative status and antioxidant responses in additional tissues are ongoing and will provide a more comprehensive understanding of the physiological implications of these feed formulations.