Microalgal omega-3 oils in salmonid aquaculture: nutritional, immunological, and sustainability perspectives beyond fish oil

1 Introduction

Salmonids are among the most economically important and intensively farmed finfish globally, ranking among the highest-value commodities in modern aquaculture. According to recent FAO production assessments, global Atlantic salmon production now exceeds 4 million tons annually, with Norway, Chile, Scotland, and Canada serving as dominant production hubs that collectively drive international seafood trade, employment, and food security (FAO, 2024; Lulijwa et al., 2022). Beyond economic value, salmonids are highly regarded for their nutritional composition, particularly their high concentrations of long-chain omega-3 polyunsaturated fatty acids (PUFAs), including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which contribute to cardiovascular, neurological, and immunological health in humans (Calder, 2018; Kolanowski, 2021). Consequently, maintaining omega-3 content in salmon fillets has become a major priority in aquaculture feed formulation and sustainable seafood production.

The rapid expansion of salmonid aquaculture has intensified pressure on global fish-oil supplies, which have remained relatively stagnant at approximately 1 million tons annually despite increasing demand from aquaculture, nutraceutical, and pharmaceutical industries (Pike and Jackson, 2010). This supply–demand imbalance has increased feed costs, market volatility, and dependence on wild-capture fisheries (Patel, 2023; Shepherd and Bachis, 2014). Several alternative lipid sources have therefore been investigated for salmonid aquafeeds, including vegetable oils, terrestrial animal fats, krill oil, yeast-derived lipids, and genetically modified oilseed crops enriched with omega-3 fatty acids. Plant-derived oils such as soybean, rapeseed, and linseed oils are economically accessible and widely available but generally lack sufficient marine-type EPA and DHA, potentially reducing fillet nutritional quality and altering inflammatory balance in farmed fish (Greene et al., 2013; Turchini et al., 2009). Terrestrial animal fats may partially improve dietary energy supply but similarly contain limited long-chain omega-3 fatty acids and may negatively influence tissue lipid composition. Krill oil provides marine-derived EPA and DHA together with phospholipid-bound omega-3s; however, large-scale utilization remains constrained by harvesting sustainability concerns, regulatory limitations, and production costs. Genetically modified oilseed crops and single-cell microbial oils have also demonstrated promising omega-3 production potential, but concerns regarding consumer acceptance, scalability, regulatory approval, and variable fatty acid profiles continue to limit widespread adoption in aquaculture systems (Sprague et al., 2017; Tocher et al., 2019). These limitations have intensified the search for sustainable lipid alternatives capable of maintaining fish health, growth efficiency, and omega-3 deposition while reducing environmental pressures associated with marine resource extraction.

Microalgal-derived oils have emerged as promising next-generation alternatives because they represent the primary natural producers of marine omega-3 fatty acids within aquatic food webs (Figure 1). Species such as Schizochytrium, Nannochloropsis, and Crypthecodinium contain high concentrations of EPA and DHA and have demonstrated strong potential to replace substantial proportions of fish oil in salmonid diets without compromising growth performance, feed conversion, survival, or fillet quality. In addition, algal oils provide EPA and DHA predominantly in bioavailable lipid forms including triacylglycerols and phospholipids, thereby supporting efficient digestion, absorption, and tissue incorporation in salmonids. Several feeding studies have further demonstrated effective deposition of algal-derived omega-3 fatty acids into muscle tissues and membrane phospholipids, helping preserve fillet nutritional quality and human dietary omega-3 intake. Beyond supporting lipid metabolism and preferential DHA retention, algal oils have also been associated with improved oxidative stress regulation, mucosal barrier integrity, inflammatory modulation, and disease resistance in cultured fish. Recent advances in algal strain engineering, closed-loop photobioreactors, carbon-capture integration, and biorefinery technologies have further improved lipid productivity and commercial scalability, positioning microalgal oils within broader circular bioeconomy and climate-resilient aquaculture frameworks aligned with Sustainable Development Goals 2, 12, and 14.

Despite these advances, important knowledge gaps remain. Existing reviews frequently evaluate nutritional performance, sustainability, or feed replacement independently, with limited integration of physiological, immunological, techno-economic, and life-cycle dimensions across salmonid production systems. Unlike previous reviews, this manuscript adopts a systems-level framework integrating salmonid nutritional physiology, mucosal immunity, lipid metabolism, feed formulation, environmental assessment, commercialization pathways, and production feasibility.

Unlike previous reviews that primarily focus on fish oil substitution, this review adopts a broader systems-level perspective on the role of microalgal oils in salmonid aquaculture. The phrase “beyond fish oil” reflects the evaluation of microalgal oils not only as alternative lipid sources but also as functional ingredients that influence salmonid physiology, immune regulation, oxidative stress responses, gut health, product quality, human nutrition, environmental sustainability, and commercial feasibility. By integrating these interconnected dimensions, the review highlights the wider biological, ecological, and industry significance of microalgal oils within future climate-resilient aquaculture systems.

By synthesizing multidisciplinary evidence, this review critically evaluates microalgal oils as functional and sustainable lipid alternatives capable of supporting nutritionally secure, environmentally resilient, and climate-adaptive salmonid aquaculture while identifying remaining technical, economic, and regulatory constraints that may influence large-scale adoption.

2 Methodology

This review was conducted to synthesize current scientific knowledge regarding the application of microalgal-derived omega-3 oils in salmonid aquaculture, with particular emphasis on nutritional physiology, fish oil replacement strategies, growth performance, fillet quality, immune regulation, sustainability, human health implications, and commercial feasibility. Literature retrieval was performed using multiple scientific databases, including Scopus, Web of Science, PubMed, ScienceDirect, and Google Scholar, to ensure comprehensive coverage of peer-reviewed literature related to aquaculture, fish nutrition, biotechnology, food science, and environmental sustainability. The overall literature search, screening, and thematic synthesis workflow employed in this review is summarized in Figure 2.

A comprehensive database search conducted between 2019 and 2024 identified a total of 5,782 records. Following removal of duplicate records (n = 2,370), 3,412 publications remained for title and abstract screening. Studies were evaluated for relevance to microalgal oils, salmonid nutrition, fish oil replacement, omega-3 fatty acid metabolism, aquafeed development, fish physiology, product quality, sustainability, and human health outcomes. After screening, 1,000 articles were retained for full-text eligibility assessment. Studies were excluded if they lacked sufficient methodological detail, were not peer-reviewed, focused on non-salmonid species without broader relevance, or did not report outcomes directly related to the objectives of this review. Following eligibility assessment, 388 studies were retained for qualitative synthesis, of which 248 studies were ultimately included in the thematic synthesis and served as the primary evidence base for this review.

The literature search employed combinations of keywords and Boolean operators including “microalgal oil,” “algal omega-3,” “EPA,” “DHA,” “salmonid aquaculture,” “Atlantic salmon,” “rainbow trout,” “fish oil replacement,” “aquafeed,” “nutrigenomics,” “microbiome,” “transcriptomics,” “metabolomics,” “fillet quality,” “immune response,” “oxidative stress,” “sustainability,” “life-cycle assessment,” and “circular bioeconomy.” Additional searches were conducted using targeted combinations associated with commercially relevant microalgal genera, including Schizochytrium, Nannochloropsis, Crypthecodinium, Isochrysis, and Phaeodactylum.

Priority was given to peer-reviewed studies published between 2019 and 2024 to ensure incorporation of recent advances in algal biotechnology, salmonid nutrition, sustainable aquafeed development, omics-based nutrition research, and commercial applications of algal-derived omega-3 oils. Earlier foundational studies were additionally included where necessary to provide physiological, biochemical, and historical context regarding long-chain omega-3 metabolism, fish oil utilization, salmonid nutritional requirements, and development of alternative aquafeed ingredients.

The review incorporated multiple categories of literature, including experimental feeding trials, nutritional physiology studies, transcriptomic and metabolomic investigations, microbiome analyses, life-cycle assessment studies, sustainability evaluations, regulatory reports, and review articles. Particular emphasis was placed on studies involving Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss), as these species represent the dominant salmonid models used in microalgal oil research and commercial aquaculture production. However, studies involving additional salmonid species were also considered where relevant to broader physiological, nutritional, and commercial implications.

Selection criteria prioritized studies reporting quantitative outcomes related to growth performance, feed conversion ratio, survival, fatty acid deposition, fillet quality, immune modulation, oxidative stress responses, microbiome interactions, contaminant accumulation, human nutritional implications, and environmental sustainability metrics. Studies lacking sufficient methodological detail, non-peer-reviewed sources, or reports with limited relevance to salmonid aquaculture and algal-derived omega-3 nutrition were excluded from primary interpretation.

The selected literature was synthesized thematically to develop an integrated perspective linking salmonid physiology, aquafeed formulation, fish health, seafood quality, human nutrition, environmental sustainability, and commercial scalability. Thematic categories included (i) nutritional importance of omega-3 fatty acids in salmonids, (ii) fish oil in traditional and evolving salmonid aquafeeds, (iii) algal oils as alternatives to fish oil, (iv) growth performance, physiology, and product quality, (v) human health implications, and (vi) sustainability and commercialization.

This approach enabled evaluation not only of the nutritional replacement potential of microalgal oils but also of their broader functional, ecological, and industrial significance within future climate-resilient aquaculture systems.

3 Nutritional importance of omega-3 fatty acids in salmonids

Omega-3 fatty acids, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are essential components of salmonid physiology and play critical roles in membrane fluidity, neural and visual development, osmoregulation, energy metabolism, and immune regulation (Barceló-Coblijn and Murphy, 2009) (Table 1). These long-chain polyunsaturated fatty acids (LC-PUFAs) are incorporated into membrane phospholipids, where they influence membrane permeability, receptor activity, cellular signaling, and mitochondrial function. DHA is especially important for neural tissues and retinal development because of its structural role in synaptic membranes and photoreceptor cells, whereas EPA functions primarily as a metabolic precursor for bioactive lipid mediators involved in inflammatory regulation and stress responses. EPA and DHA additionally serve as substrates for specialized pro-resolving mediators, including resolvins, protectins, and maresins, which regulate inflammatory homeostasis, tissue repair, and immune recovery. In salmonids, these physiological functions become particularly important during rapid growth, smoltification, reproduction, and environmental stress adaptation (Calder et al., 2020). Because these species possess limited endogenous capacity to synthesize sufficient EPA and DHA from precursor fatty acids, adequate dietary provision of long-chain omega-3 fatty acids becomes nutritionally essential under intensive aquaculture conditions.

Table 1. Functional roles of EPA and DHA in salmonid physiology (adapted from Calder, 2018; Tocher, 2015; Barceló-Coblijn and Murphy, 2009).

EPA, eicosapentaenoic acid; DHA, docosahexaenoic acid; ARA, arachidonic acid.

Beyond their structural roles, EPA and DHA are fundamental regulators of physiological performance in salmonids. These fatty acids contribute to the maintenance of cellular membrane integrity, optimization of nutrient transport, and regulation of metabolic pathways associated with growth and energy utilization. DHA is preferentially retained in neural and visual tissues because of its importance in maintaining membrane fluidity and neuronal function, whereas EPA is more actively involved in immune modulation through its role as a precursor of eicosanoids and specialized pro-resolving mediators. Together, these fatty acids influence stress responsiveness, inflammatory balance, and disease resistance, thereby contributing to overall fish health and production performance.

Despite their physiological importance, salmonids exhibit limited enzymatic capacity to convert plant-derived α-linolenic acid (ALA) into long-chain omega-3 fatty acids through desaturation and elongation pathways (Tocher, 2015). Consequently, endogenous synthesis alone is insufficient to satisfy physiological demands in modern aquaculture systems, where rapid growth performance, feed efficiency, and stress resilience are essential. Adequate dietary provision of preformed EPA and DHA therefore remains critical for maintaining optimal growth, immune competence, metabolic regulation, reproductive performance, and fillet quality.

The importance of EPA and DHA extends beyond fish physiology to the nutritional quality of salmonid products intended for human consumption. Deposition of these fatty acids in muscle tissues contributes significantly to the value of salmonids as dietary sources of long-chain omega-3 fatty acids. High tissue concentrations of EPA and DHA enhance the nutritional profile of salmon fillets and support the recognized cardiovascular, neurological, and immunological benefits associated with seafood consumption. Consequently, maintaining adequate levels of these fatty acids throughout production remains a central objective in salmonid nutrition and aquaculture management.

Figure 3 illustrates the major metabolic, immunological, and nutritional functions of EPA and DHA in salmonids, highlighting their roles in membrane phospholipid remodeling, inflammatory regulation, oxidative stress responses, tissue omega-3 deposition, and overall physiological performance.

4 Fish oil in traditional and evolving salmonid aquafeeds

Fish oil has historically served as the principal lipid source in salmonid aquafeeds because of its high digestibility, favorable fatty acid profile, and rich concentrations of the long-chain omega-3 polyunsaturated fatty acids (LC-PUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These fatty acids are essential for supporting optimal growth, feed utilization, immune competence, stress resilience, reproductive performance, and fillet quality in Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) (Bell et al., 1997; Tocher, 2015). Because salmonids possess limited endogenous capacity to synthesize sufficient EPA and DHA from shorter-chain precursors, fish oil has long been regarded as the most effective dietary source of these physiologically important nutrients (Turchini and Francis, 2009).

The nutritional value of fish oil extends beyond its role as an energy source. Fish oil provides highly bioavailable EPA and DHA that are efficiently incorporated into membrane phospholipids, neural tissues, and muscle lipids. Numerous studies have demonstrated that fish oil-rich diets support superior growth performance, feed conversion efficiency, survival, and immune responsiveness compared with diets deficient in marine-derived lipids (Bell & Waagbø, 2008; Sargent et al., 2002). Furthermore, dietary fish oil contributes to maintenance of desirable tissue omega-3 concentrations, thereby preserving the nutritional quality of salmon fillets and supporting the well-documented cardiovascular and neurological benefits associated with salmon consumption (Calder et al., 2020). These characteristics have established fish oil as the nutritional benchmark against which alternative lipid sources are evaluated.

Beyond growth and nutritional quality, fish oil plays an important role in maintaining physiological homeostasis in salmonids. Dietary EPA and DHA influence membrane fluidity, cellular signaling, osmoregulation, inflammatory regulation, and stress adaptation, particularly during critical life-history stages such as smoltification, reproduction, and environmental transition. The balance between omega-3 and omega-6 fatty acids supplied by fish oil also contributes to regulation of eicosanoid synthesis and immune function, supporting disease resistance and recovery from physiological stressors. Consequently, fish oil has remained a key functional ingredient in commercial salmonid feeds for several decades.

Despite its nutritional advantages, the long-term sustainability of fish oil has become an increasing concern. Global fish oil production remains largely dependent on wild-capture forage fisheries and has remained relatively stable despite the continuous expansion of the aquaculture sector (Pike and Jackson, 2010; Shepherd and Bachis, 2014). This imbalance between supply and demand has contributed to rising prices, market volatility, and increased competition among aquaculture, nutraceutical, and pharmaceutical industries. Furthermore, concerns regarding overexploitation of forage fish stocks, ecosystem impacts, and climate-related variability have intensified scrutiny of continued dependence on marine-derived feed ingredients (Naylor et al., 2021).

In response to these challenges, considerable efforts have been directed toward reducing fish oil inclusion levels through the use of alternative lipid sources. Terrestrial oils such as rapeseed, soybean, linseed, and poultry oils have been evaluated as partial fish oil substitutes because of their availability and lower cost. Several studies demonstrated that moderate substitution levels can maintain growth and survival in salmonids; however, excessive replacement often reduces tissue EPA and DHA concentrations, alters membrane lipid composition, and diminishes fillet nutritional quality (Rosenlund et al., 2002; Sprague et al., 2016a; Turchini et al., 2009). In addition, replacement of marine lipids with vegetable oils may disrupt the balance between eicosapentaenoic acid (EPA) and arachidonic acid (ARA), potentially affecting inflammatory regulation, immune competence, and stress responsiveness (Calder, 2018; Tocher, 2015). Although compensatory expression of fatty acid desaturase and elongase enzymes may occur, endogenous biosynthesis remains insufficient to fully restore tissue long-chain omega-3 levels in salmonids (Leaver et al., 2008; Stubhaug et al., 2005).

Collectively, these nutritional, economic, and environmental challenges highlight the need for sustainable lipid sources capable of maintaining the functional benefits traditionally provided by fish oil. As the aquaculture industry seeks to reduce dependence on finite marine resources while preserving fish performance and fillet omega-3 quality, increasing attention has been directed toward novel sources of EPA and DHA. Figure 4 summarizes the evolving role of fish oil in salmonid nutrition and the factors driving the transition toward alternative omega-3 sources. The potential of microalgal oils as sustainable replacements for fish oil is discussed in the following section.

5 Algal oils as alternatives to fish oil in salmonid aquaculture

Marine microalgae have emerged as promising alternatives to fish oil because they are the primary natural producers of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) within aquatic food webs. Species such as Schizochytrium, Ulkenia, Nannochloropsis, and Crypthecodinium cohnii synthesize substantial quantities of long-chain omega-3 fatty acids and produce lipid classes, including triacylglycerols and phospholipids, that are readily utilized by salmonids (Harwood, 2019; Topuz, 2016; Topf et al., 2012; Ansorena and Astiasarán, 2013). Advances in cultivation and extraction technologies have improved the commercial availability of algal oils, making them increasingly attractive as sustainable alternatives to conventional marine lipids. Compared with fish oil, algal oils offer the advantage of providing direct sources of EPA and DHA while reducing dependence on finite wild-capture fisheries.

The lipid composition of commercially important microalgae varies considerably among species, resulting in differences in EPA and DHA content, digestibility, fatty acid deposition, oxidative stability, and suitability for salmonid feed applications. As summarized in Table 2, DHA-rich species such as Schizochytrium and Crypthecodinium cohnii are particularly effective for restoring tissue DHA concentrations, whereas EPA-rich species such as Nannochloropsis and Phaeodactylum tricornutum may contribute to maintenance of membrane phospholipid composition and inflammatory regulation. Other species, including Isochrysis galbana and Tetraselmis spp., provide additional bioactive compounds such as phospholipids, carotenoids, and immunostimulatory metabolites that may enhance fish health and physiological performance.

Table 2. EPA and DHA composition characteristics of major microalgal species used in salmonid aquaculture.

Values may vary depending on cultivation conditions, nutrient availability, strain selection, and extraction methods.

As shown in Table 2, substantial variability exists among microalgal species in terms of fatty acid composition and functional applications. These differences are particularly important because the relative proportions of EPA and DHA directly influence tissue omega-3 deposition, fillet nutritional quality, immune modulation, and physiological responses in salmonids. Consequently, the selection of appropriate microalgal species and formulation strategies remains critical for optimizing fish performance while maximizing retention of beneficial long-chain omega-3 fatty acids.

One of the most important considerations in evaluating algal oils as fish oil alternatives is their ability to maintain tissue EPA and DHA concentrations following partial or complete fish oil replacement. The effectiveness of microalgal oils depends not only on species composition but also on the level of fish oil substitution and the resulting retention of omega-3 fatty acids in fish tissues. Figure 5 illustrates the relationship between fish oil replacement levels, omega-3 retention, physiological performance, and sustainability outcomes in salmonid aquaculture.

Numerous feeding trials have evaluated partial and complete replacement of fish oil with microalgal oils in salmonid diets. As shown in Table 3, replacement levels ranging from 25% to 100% can maintain growth performance and feed efficiency when sufficient dietary EPA and DHA are supplied. Partial replacement strategies (approximately 25–50% substitution) generally preserve growth, feed conversion efficiency, and tissue omega-3 concentrations while reducing dependence on marine-derived fish oil. Such inclusion levels frequently provide adequate long-chain omega-3 fatty acids to support normal physiological function and maintain fillet nutritional quality.

Table 3. Fish oil replacement levels and omega-3 retention outcomes in salmonids fed microalgal oils.

EPA retention responses vary according to the fatty acid composition of the microalgal source. DHA-rich microalgae such as Schizochytrium spp. consistently maintain tissue DHA concentrations, whereas EPA retention may require inclusion of EPA-rich species or mixed algal formulations (Kousoulaki et al., 2015; Sprague et al., 2017; Islam et al., 2024).

Higher replacement levels (50–100%) have also demonstrated promising outcomes, particularly when DHA-rich species such as Schizochytrium are used. Several studies have reported maintenance of growth performance, survival, and feed conversion ratios comparable to fish oil-based diets despite substantial reductions in fish oil inclusion. Complete replacement strategies have proven feasible under optimized dietary formulations, indicating that microalgal oils can effectively supply the essential long-chain omega-3 fatty acids required by salmonids. Several studies further reported maintenance of DHA deposition despite high fish oil replacement levels, with DHA retention remaining comparable to fish oil-fed controls in diets containing DHA-rich microalgal oils such as Schizochytrium spp (Kousoulaki et al., 2015; Islam et al., 2024). This observation is particularly important because preservation of tissue DHA concentrations helps maintain fillet nutritional quality and the value of salmonids as dietary sources of long-chain omega-3 fatty acids.

Although growth performance is often maintained at high replacement levels, omega-3 retention responses may vary depending on the fatty acid composition of the microalgal source. DHA-rich species generally maintain or restore tissue DHA concentrations, whereas EPA retention can be more variable because many commercially available microalgae contain relatively low EPA levels. Consequently, combinations of EPA-rich and DHA-rich microalgal species may offer a more balanced strategy for maintaining both tissue EPA and DHA concentrations in salmonids.

As shown in Table 2, substantial variability exists among microalgal species in terms of EPA and DHA composition, lipid class distribution, and functional applications in aquafeeds. These differences are important because DHA-rich species such as Schizochytrium are more suitable for restoring fillet DHA concentrations in Atlantic salmon, whereas EPA-rich species such as Nannochloropsis may support inflammatory regulation and membrane phospholipid balance. Consequently, the selection of appropriate microalgal species and formulation strategies remains critical for optimizing fish growth, tissue omega-3 deposition, fillet nutritional quality, and feed sustainability in salmonid aquaculture systems.

Evidence from controlled feeding studies further demonstrates the practical feasibility of using microalgal oils in commercial salmonid aquaculture. Table 4 summarizes representative feeding trials evaluating different microalgal species, fish oil replacement levels, omega-3 retention outcomes, growth performance, and physiological responses in Atlantic salmon and rainbow trout. For example, Schizochytrium-derived oils have demonstrated digestibility exceeding 96% while maintaining tissue EPA+DHA concentrations comparable to those in fish oil-fed Atlantic salmon (Norambuena et al., 2015). Similarly, Kousoulaki et al. (2015) reported complete replacement of fish oil while maintaining growth performance, feed conversion ratios between 0.8 and 0.9, and DHA deposition comparable to conventional diets. More recent studies have demonstrated that fish oil replacement levels of 50–100% can preserve tissue omega-3 concentrations, maintain survival rates exceeding 98%, and improve immune-related responses, including mucosal barrier integrity and antioxidant defense mechanisms (Islam et al., 2024; Santigosa et al., 2023).

Table 4. Summary of feeding trials evaluating microalgal oils as alternatives to fish oil in salmonid aquaculture.

Quantitative measurements of EPA and DHA retention were not uniformly reported across all studies reviewed. Consequently, qualitative descriptions of omega-3 retention and lipid outcomes are provided where standardized quantitative comparisons were unavailable.

6 Effects of algal oils on farmed salmonids

6.1 Growth performance, physiology, and product quality

6.1.1 Growth performance

Numerous feeding trials have demonstrated that microalgal oils can effectively replace fish oil in salmonid diets without compromising growth performance, feed efficiency, survival, or tissue omega-3 deposition. Studies involving Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) consistently report that partial and complete fish oil replacement with microalgal oils maintains production performance comparable to conventional fish oil-based diets (Norambuena et al., 2015; Santigosa et al., 2020, Santigosa et al., 2023; Zatti et al., 2023). In Atlantic salmon, dietary inclusion of DHA-rich Schizochytrium spp. oils-maintained feed conversion ratios (FCRs) between 0.8 and 1.0 while preserving survival rates exceeding 95% and sustaining DHA deposition at levels comparable to fish oil-fed controls (Kousoulaki et al., 2015; Sprague et al., 2015). Similarly, fish oil replacement levels ranging from 50% to 100% have been reported to maintain growth performance and support survival rates above 98% while preserving tissue EPA and DHA concentrations when adequate dietary long-chain omega-3 fatty acids are supplied (Islam et al., 2024). Comparable outcomes have also been observed in rainbow trout, where algal-derived omega-3 lipids supported normal growth rates, protein utilization efficiency, and fillet sensory characteristics without significant differences from conventional fish oil-based diets (Norambuena et al., 2015). Collectively, these findings indicate that microalgal oils can sustain productive performance across a broad range of replacement levels while reducing reliance on finite marine-derived lipid resources.

6.1.2 Physiological responses and fish health

Beyond growth performance, microalgal oils influence several physiological processes associated with fish health, nutrient utilization, and environmental adaptation. The high DHA content of many microalgal oils contributes to membrane fluidity, neural development, mitochondrial function, and maintenance of tissue omega-3 concentrations, all of which support physiological stability under intensive aquaculture conditions. Feeding trials have consistently reported maintenance of normal gut morphology and digestive function following partial or complete replacement of fish oil with microalgal oils (Kousoulaki et al., 2015; Santigosa et al., 2023). In Atlantic salmon, complete replacement of fish oil with Schizochytrium-derived oils increased intestinal goblet cell abundance and enhanced inducible nitric oxide synthase (iNOS) activity, suggesting improved mucosal defense mechanisms and intestinal health (Kousoulaki et al., 2015). Maintenance of tissue EPA and DHA concentrations further contributes to membrane integrity, cellular signaling pathways, and metabolic regulation, which are critical for sustaining physiological performance under commercial production conditions.

Microalgal oils have also been associated with positive effects on immune competence and stress-response pathways. Dietary supplementation with algal-derived omega-3 fatty acids has been linked to improved mucosal barrier integrity, enhanced expression of immune-related genes, and more effective regulation of inflammatory responses in salmonids (Islam et al., 2024; Kousoulaki et al., 2015). Furthermore, dietary microalgae influence endocrine and stress-related pathways involving cortisol regulation, heat shock proteins (HSP70 and HSP90), and inflammatory mediators associated with thermal stress, crowding, and hypoxic exposure (Santigosa et al., 2023; Vijayan et al., 2003). These physiological responses may contribute to improved resilience and adaptation to environmental challenges commonly encountered in intensive aquaculture systems.

The physiological effects of microalgal oils are influenced by species, genetic background, and developmental stage because salmonids differ in lipid metabolism, fatty acid deposition patterns, and nutrient utilization efficiency. Atlantic salmon generally exhibit efficient DHA deposition and have therefore served as the primary model species in studies investigating complete fish oil replacement using DHA-rich microalgal oils such as Schizochytrium spp. In contrast, rainbow trout may display different patterns of fatty acid metabolism and tissue lipid deposition that influence EPA and DHA retention and overall responses to dietary lipid sources (Tocher, 2015; Turchini et al., 2009). Nutritional requirements also vary throughout the production cycle, with broodstock, juvenile, and grow-out stages exhibiting different demands for long-chain omega-3 fatty acids. Studies involving broodstock nutrition have demonstrated that microalgal oils can enhance egg DHA deposition, maintain broodstock nutritional status, and support larval viability and fry survival rates comparable to those achieved using conventional fish oil-based diets (Cardona et al., 2022; Johnson et al., 2011). Nevertheless, although elevated DHA inclusion generally improves tissue omega-3 retention and physiological performance, excessive enrichment with highly unsaturated fatty acids may increase susceptibility to lipid peroxidation and oxidative stress. Consequently, balanced EPA-to-DHA ratios and appropriate antioxidant stabilization strategies remain important considerations for maintaining feed quality and fish health under high-inclusion feeding regimes.

6.1.3 Product quality and nutritional value

In addition to supporting fish growth and physiological health, microalgal oils contribute to maintaining and, in some cases, enhancing the nutritional quality and safety of salmonid products intended for human consumption. One of the principal advantages of microalgal oils is their ability to preserve tissue EPA and DHA concentrations, which directly determine the nutritional value of salmonid fillets. Multiple studies have reported maintenance of tissue omega-3 deposition and fillet sensory characteristics following replacement of fish oil with algal oils, indicating that product quality can be preserved despite substantial reductions in marine-derived feed ingredients (Norambuena et al., 2015; Sprague et al., 2015; Zatti et al., 2023). Preservation of tissue EPA and DHA is particularly important because these fatty acids contribute to the cardiovascular, neurological, and immunological benefits associated with salmon consumption.

Microalgal oils may also improve product safety by reducing the accumulation of environmental contaminants commonly associated with marine-derived feed ingredients. Several studies have reported reductions of approximately 40–79% in persistent organic pollutants, including polychlorinated biphenyls (PCBs) and dioxins, in salmonids fed algal-oil-based diets while maintaining tissue omega-3 concentrations and consumer-acceptable fillet quality (Santigosa et al., 2021; Zatti et al., 2023). Such reductions enhance the safety profile of farmed salmonid products and may increase consumer confidence in aquaculture-derived seafood. Regulatory approvals from the European Food Safety Authority (EFSA), the United States Food and Drug Administration (FDA), and the United States Department of Agriculture (USDA) further support the commercial use of algal oils in aquafeeds (Glencross et al., 2020).

Beyond product quality, the adoption of microalgal oils also contributes to broader sustainability objectives within aquaculture. Life-cycle assessment studies suggest that replacing fish oil with microalgal oils may reduce greenhouse gas emissions by approximately 30–40% while decreasing freshwater and land-use requirements, particularly when integrated with circular bioeconomy approaches or integrated multi-trophic aquaculture (IMTA) systems (Davis et al., 2021; Mendoza Beltran et al., 2018; Togarcheti and Padamati, 2021). Taken together, current evidence demonstrates that microalgal oils can simultaneously support growth performance, physiological health, fillet nutritional quality, product safety, and environmental sustainability, reinforcing their potential as next-generation lipid sources for salmonid aquaculture.

6.2 Nutrient–microbiota–immunity interactions in salmonids

Increasing evidence indicates that algal oils modulate salmonid health through a complex nutrient–microbiota–immunity nexus involving interactions among dietary omega-3 lipids, gut microbial communities, intestinal epithelial integrity, and host immune signaling pathways (Figure 6). Dietary microalgae-derived lipids can alter gut microbial diversity and selectively enrich beneficial bacterial taxa associated with nutrient metabolism, mucosal homeostasis, and immune competence. In rainbow trout, low-level microalgae supplementation increased distal intestinal microbial diversity and promoted the abundance of potentially beneficial genera such as Lactobacillus and Streptococcus (Lyons et al., 2016). Similarly, Atlantic salmon fed Schizochytrium-derived oils exhibited enhanced mucosal barrier function, increased mucous cell density in intestinal, skin, and gill tissues, and improved epithelial integrity following seawater transfer challenges (Islam et al., 2024). Collectively, these findings suggest that algal oils contribute to stabilization of host–microbiota interactions and reinforcement of epithelial defense mechanisms under intensive aquaculture conditions.

The immunomodulatory effects of algal oils are additionally associated with regulation of cytokine signaling pathways, antimicrobial peptide expression, and innate immune activation. Dietary inclusion of microalgae has been shown to influence transcription of immune-related genes including muc2, muc5ac, def3, cath1, complement component C3, and NK-lysine genes, indicating enhanced mucosal immunity and antimicrobial defense capacity (Islam et al., 2024; Sánchez et al., 2023). Transcriptomic investigations in Atlantic salmon further demonstrated altered expression of cytokine receptor-associated genes such as il1r2 and il10rb, suggesting modulation of inflammatory signaling and immune homeostasis following dietary microalgal supplementation (Mueller et al., 2023). Although direct evidence regarding toll-like receptor (TLR) pathway activation in salmonids remains limited, EPA- and DHA-rich algal oils are known to regulate inflammatory mediators and eicosanoid biosynthesis, thereby influencing innate immune responsiveness and cytokine balance (Bahi et al., 2023). Collectively, these mechanisms support the concept that algal oils act not only as lipid sources but also as functional bioactive ingredients capable of modulating host immune physiology.

Microalgal oils also contribute to oxidative stress regulation and intestinal functionality through interactions between lipid metabolism, epithelial integrity, and immune signaling. Feeding studies demonstrated improvements in respiratory burst activity, lysozyme activity, phagocytic capacity, and antioxidant enzyme activities including superoxide dismutase, catalase, and glutathione peroxidase in salmonids receiving algal oil supplementation (Bahi et al., 2023; Islam et al., 2024; Santigosa et al., 2023). In Atlantic salmon, Schizochytrium supplementation enhanced goblet cell production and inducible nitric oxide synthase (iNOS) activity in intestinal tissues, further supporting mucosal barrier functionality and local immune defense (Kousoulaki et al., 2015). Emerging transcriptomic, metabolomic, and microbiome-based investigations additionally suggest that algal-derived omega-3 fatty acids may influence lipid mediator biosynthesis, cellular energy metabolism, redox homeostasis, and microbe-associated metabolic pathways linked to nutrient utilization and intestinal health (Morais et al., 2011). Integration of multi-omics approaches therefore provides an increasingly important framework for understanding how dietary algal oils regulate host–microbiota interactions, epithelial barrier integrity, and immune competence in salmonids.

Nevertheless, several limitations remain unresolved, including high production costs, oxidative instability of highly unsaturated lipids, digestibility variability among algal taxa, and potential stage-specific metabolic constraints during early development or environmental stress exposure. Evidence regarding microbiome-mediated mechanisms also remains relatively limited, as most available studies involve short-term feeding trials ranging from approximately 7 to 13 weeks and focus primarily on Atlantic salmon and rainbow trout. Furthermore, several studies suggest that partial fish oil replacement (approximately 50%) may produce more consistent microbiota and mucosal immune benefits than complete replacement strategies, indicating that optimal inclusion thresholds remain species- and context-dependent. Consequently, future research should prioritize long-term multi-cycle feeding studies, climate-stress interactions, microbiome-mediated immune regulation, optimization of strain-specific DHA/EPA production, and integrative multi-omics approaches to improve both biological performance and commercial scalability of algal oil-based aquafeeds in salmonid aquaculture.

7 Human health implications

7.1 Health benefits of salmonid consumption

Long-chain omega-3 polyunsaturated fatty acids (LC-PUFAs), particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are among the most extensively studied dietary nutrients because of their established roles in human health. Numerous epidemiological studies and clinical trials have demonstrated that regular consumption of EPA- and DHA-rich seafood is associated with a reduced risk of cardiovascular disease, improved lipid metabolism, lower circulating triglyceride concentrations, and favorable modulation of inflammatory pathways implicated in chronic diseases (Calder et al., 2020; Mozaffarian & Rimm, 2006). These fatty acids serve as precursors for specialized pro-resolving mediators, including resolvins and protectins, which contribute to the resolution of inflammation and maintenance of immune homeostasis. Consequently, regular dietary intake of EPA and DHA is widely recommended as part of a healthy dietary pattern to support cardiovascular and metabolic health.

Docosahexaenoic acid is also a critical structural component of neural and retinal tissues, making adequate dietary intake particularly important during pregnancy, infancy, and childhood. Maternal consumption of omega-3-rich seafood has been associated with improved fetal neurodevelopment, visual acuity, and cognitive outcomes in offspring, while continued dietary intake throughout life contributes to maintenance of normal brain function and healthy aging (Calder et al., 2020). Emerging evidence additionally suggests that higher consumption of long-chain omega-3 fatty acids may support cognitive performance and reduce the risk of age-related cognitive decline, although the magnitude of these effects varies among populations and study designs.

Among commonly consumed seafood products, salmonids such as Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) are recognized as some of the richest dietary sources of EPA and DHA. A single serving of salmon can provide several hundred milligrams to more than one gram of combined EPA and DHA, contributing substantially toward recommended dietary intakes established by organizations such as the World Health Organization (WHO), the American Heart Association (AHA), and the European Food Safety Authority (EFSA). In addition to omega-3 fatty acids, salmonid fillets provide high-quality protein, essential amino acids, vitamin D, vitamin B12, selenium, iodine, and antioxidant carotenoids such as astaxanthin, which collectively support immune function, skeletal health, neurological function, and healthy aging (Ruxton et al., 2004).

The public health importance of salmonid consumption extends beyond individual physiological benefits. In many regions, dietary intake of EPA and DHA remains below recommended levels because of limited seafood consumption and changing dietary patterns. Salmonids therefore represent an important and accessible food source capable of helping address population-level deficiencies in long-chain omega-3 fatty acids. Their widespread availability in fresh, frozen, smoked, canned, and value-added forms further enhances their contribution to food and nutrition security. As global demand for healthy and sustainable protein sources continues to increase, maintaining the nutritional quality of salmonid products remains an important objective for both aquaculture production and public health.

7.2 Contribution of salmonids to nutrition security and food safety

The growing global demand for nutrient-rich foods has increased the importance of aquaculture as a reliable source of healthy animal protein and essential micronutrients. Salmonid aquaculture contributes significantly to food and nutrition security by providing a consistent supply of EPA- and DHA-rich seafood independent of fluctuations in wild fish stocks. The ability of farmed salmonids to efficiently convert dietary nutrients into highly nutritious fillets makes them valuable components of sustainable food systems designed to support growing human populations while maintaining nutritional quality.

Product quality and safety are equally important determinants of the public health value of salmonid products. Consumers increasingly seek seafood products that provide high nutritional value while minimizing exposure to environmental contaminants. Research has demonstrated that modern aquaculture practices can maintain desirable concentrations of beneficial omega-3 fatty acids while simultaneously reducing exposure to contaminants such as dioxins and polychlorinated biphenyls (PCBs), thereby enhancing the overall health value of farmed seafood products (Zatti et al., 2023). Preservation of both nutrient quality and food safety is essential for maintaining consumer confidence and maximizing the public health benefits associated with regular salmon consumption.

7.3 Role of microalgal oils in preserving human nutritional benefits

The principal public health value of salmonid consumption lies in its ability to provide substantial amounts of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), two long-chain omega-3 fatty acids associated with numerous health benefits throughout the human lifespan. Adequate intake of EPA and DHA has been linked to reduced cardiovascular disease risk, lower plasma triglyceride concentrations, improved endothelial function, enhanced neurodevelopment, maintenance of cognitive performance, visual health, immune regulation, and modulation of chronic inflammatory processes (Calder et al., 2020; Mozaffarian & Rimm, 2006; Ruxton et al., 2004). Because salmonids represent one of the richest dietary sources of these nutrients, preserving their omega-3 content is essential for maintaining the nutritional and functional value of salmon products available to consumers.

The continued availability of salmon fillets containing high concentrations of EPA and DHA is particularly important in regions where seafood consumption remains below recommended levels and dietary omega-3 intake is insufficient. Regular consumption of omega-3-rich salmon products contributes significantly to achieving recommended intakes of long-chain omega-3 fatty acids and supports broader public health objectives related to cardiovascular health, cognitive function, healthy aging, and maternal and infant nutrition (Calder et al., 2020). Preservation of these nutrients within farmed salmon therefore has implications not only for individual health outcomes but also for population-level nutrition security.

Recent feeding studies demonstrate that salmonids produced using diets containing microalgal-derived omega-3 oils retain tissue EPA and DHA concentrations capable of supporting recommended human dietary intakes (Santigosa et al., 2023; Sprague et al., 2015). In Atlantic salmon, replacement of fish oil with Schizochytrium-derived oils maintained DHA deposition and fillet sensory quality comparable to conventional fish oil-based diets (Sprague et al., 2015; Zatti et al., 2023). Consequently, consumers can continue to obtain the recognized cardiovascular, neurological, developmental, and immunological benefits associated with salmon consumption even when alternative and more sustainable omega-3 sources are incorporated into aquaculture feeds.

Beyond maintaining omega-3 content, salmon products derived from algal-oil-based production systems may offer additional public health advantages through improved food safety. Studies have reported reductions of approximately 70–80% in contaminant concentrations, including dioxins and polychlorinated biphenyls (PCBs), in salmon produced using algal-oil feeding strategies while maintaining desirable EPA and DHA levels (Zatti et al., 2023). Reduced contaminant exposure enhances the overall health value of salmon products and may increase consumer confidence in aquaculture-derived seafood. Furthermore, sensory evaluations indicate that replacement of fish oil with algal-derived oils generally preserves fillet taste, texture, color, and overall consumer acceptability, ensuring that nutritional and safety improvements are not achieved at the expense of product quality (Rudd et al., 2011; Sprague et al., 2016b).

The use of algal-derived omega-3 ingredients has received regulatory approval from authorities including the United States Food and Drug Administration (FDA) and the European Food Safety Authority (EFSA), reflecting their recognized safety and suitability for food production systems (Ververis et al., 2020; Lee et al., 2022). Ultimately, the importance of microalgal oils from a human-health perspective lies not in their role as feed ingredients, but in their capacity to sustain the production of nutritionally rich salmon products that continue to deliver essential omega-3 fatty acids, support cardiovascular and neurological health, improve food safety, and contribute to global nutrition security within increasingly sustainable aquaculture systems.

8 Economic viability, commercial adoption, and implementation challenges

8.1 Economic viability and commercial adoption

Commercial adoption of algal oils in salmon aquafeeds has accelerated substantially over the past decade as aquaculture producers seek more stable and sustainable alternatives to conventional marine lipids. Since 2018, industrial-scale incorporation of algal oils into Norwegian salmon feeds has increased steadily, with reports indicating that approximately 30% of commercial salmon feed formulations in Norway incorporated some level of algal-derived omega-3 ingredients by the early 2020s (Zatti et al., 2023). This transition has been driven by increasing volatility in global fish oil markets, pressure to reduce Fish-In Fish-Out (FIFO) ratios, sustainability certification requirements, and growing consumer demand for environmentally responsible seafood products.

Commercial biotechnology companies including Veramaris, Corbion, and DSM-Firmenich have emerged as major industrial suppliers of algal-derived omega-3 oils for aquaculture and nutraceutical markets, demonstrating the growing integration of microalgal biotechnology into global aquafeed supply chains. As illustrated in Figure 7, economic integration of algal oils involves interconnected industrial, environmental, and market components including commercial production systems, feed-cost modeling, sustainability certification, circular bioeconomy integration, and expanding omega-3 markets.

The projected expansion of the global aquafeed sector, increasing demand for sustainable omega-3 ingredients, and continued growth of nutraceutical and functional-food industries are expected to strengthen the long-term market outlook for algal oils. Although algal oils currently increase feed formulation costs, broader economic assessments suggest that several indirect benefits may improve medium- and long-term profitability. Enhanced feed efficiency, improved fish health, reduced contaminant accumulation, premium product positioning, and increasing consumer willingness-to-pay for sustainable seafood products may partially offset higher ingredient costs. Furthermore, algal cultivation systems can utilize non-arable land, saline water, industrial CO₂ streams, and wastewater nutrient recovery systems, thereby reducing freshwater demand and environmental pressure associated with conventional agriculture and marine resource extraction (Ahmed et al., 2012; Chary et al., 2024; Pereira et al., 2024; Verma and Mishra, 2020). Integration of algal biotechnology into circular bioeconomy frameworks may therefore provide strategic advantages beyond direct feed economics, including carbon sequestration potential, improved supply-chain resilience, and enhanced alignment with global sustainability and nutrition-security objectives.

8.2 Challenges and limitations

Despite strong commercial momentum, economic competitiveness remains one of the primary constraints limiting widespread adoption of algal oils in salmonid aquaculture. Current algal oil production costs generally range from approximately US$7–12 kg⁻¹ compared with US$3–6 kg⁻¹ for conventional fish oil, largely because of high capital expenditures (CAPEX) associated with cultivation infrastructure and substantial operational expenditures (OPEX) related to energy consumption, aeration, nutrient supply, harvesting, and downstream lipid extraction (Akhila et al., 2024; Chisti, 2013). Feed cost modeling studies indicate that lipid ingredients remain among the most economically sensitive components of salmonid diets, and profitability therefore depends heavily on production scale, feed conversion efficiency, and market price premiums associated with sustainable seafood certification (Asche et al., 2007; Naylor et al., 2021; Tacon & Metian, 2015). Consequently, the long-term economic feasibility of algal oils will depend not only on reductions in production costs but also on improvements in feed efficiency, supply-chain stability, sustainability performance, and consumer willingness-to-pay for environmentally responsible seafood products.

Technical and biological limitations additionally continue to influence industrial scalability and reliability. Upstream cultivation systems remain vulnerable to contamination, strain instability, variable EPA/DHA productivity, photobioreactor fouling, and environmental fluctuations that may reduce lipid yields. Downstream processing, particularly biomass harvesting, drying, and lipid extraction, represents one of the most energy-intensive stages of production and strongly affects overall economic feasibility (Ahmad et al., 2022; Mercer and Armenta, 2011; Weyer et al., 2010). Heterotrophic production systems generally require energy inputs of approximately 50–60 MJ kg⁻¹ oil, whereas phototrophic systems require approximately 30–40 MJ kg⁻¹ oil, both exceeding the energy intensity of traditional fish oil processing despite providing greater supply stability and reduced ecological volatility.

Additional nutritional and formulation challenges also remain unresolved. Highly unsaturated algal lipids may exhibit increased susceptibility to oxidative degradation during feed processing and storage, thereby requiring antioxidant stabilization strategies and optimized formulation approaches. Digestibility and fatty acid bioavailability may further vary among algal taxa and production systems, potentially influencing omega-3 deposition and physiological performance in salmonids. Moreover, algal oils currently compete with other emerging omega-3 alternatives including genetically modified oilseeds and yeast-derived lipids such as Yarrowia lipolytica, prompting many feed manufacturers to adopt blended lipid strategies that optimize cost, fatty acid composition, and sustainability performance (Topf et al., 2012).

Regulatory frameworks also vary among regions and may influence commercial adoption rates. Although approvals from the European Food Safety Authority (EFSA) and the United States Food and Drug Administration (FDA) have facilitated commercialization and increased industry confidence in algal-derived feed ingredients (Ververis et al., 2020; U.S. Food and Drug Administration, 2019), differences in regulatory approval pathways, labeling requirements, and sustainability certification standards continue to create implementation challenges across global aquaculture markets.

Consequently, the long-term economic viability of algal oils will likely depend not only on reductions in production costs but also on continued improvements in cultivation efficiency, strain engineering, renewable-energy integration, feed formulation strategies, and the ability of aquaculture industries to capture environmental, nutritional, and market-based value associated with sustainable omega-3 production systems.

9 Future perspectives and research directions

Although substantial progress has been achieved in the development of microalgal oils for salmonid aquaculture, several biological, technological, and industrial questions remain insufficiently resolved. Therefore, future research must move beyond simple fish-oil replacement studies toward integrated frameworks that evaluate long-term physiological adaptation, nutritional precision, environmental resilience, and commercial scalability across diverse salmonid production systems.

One important priority the involves refinement of species-specific lipid nutrition strategies. Current evidence is derived predominantly from Atlantic salmon and rainbow trout, whereas comparatively limited information exists for other salmonids such as Arctic charr, coho salmon, Chinook salmon, and brown trout. Future studies should therefore investigate interspecific differences in fatty acid metabolism, omega-3 deposition efficiency, stress responsiveness, immune regulation, and reproductive performance to determine whether nutritional responses to algal oils can be generalized across salmonid taxa.

Additional attention is also required toward optimization of EPA ratios and lipid class composition in aquafeeds. While many studies demonstrate successful replacement of fish oil using DHA-rich algal sources, less is understood regarding the long-term physiological consequences of altered EPA balance, membrane remodeling, and oxidative susceptibility under intensive farming conditions. Greater understanding of lipid partitioning, tissue-specific fatty acid deposition, and metabolic regulation will be essential for improving both fish performance and fillet nutritional quality.

Emerging omics technologies provide particularly promising opportunities for advancing mechanistic understanding of algal-oil utilization in salmonids. Integrated transcriptomic, metabolomic, lipidomic, and microbiome analyses may help identify molecular biomarkers associated with immune competence, intestinal health, oxidative stress resilience, nutrient utilization efficiency, and climate-stress adaptation. Such approaches could substantially improve understanding of the nutrient–microbiota–immunity nexus highlighted throughout this review while supporting the development of precision aquaculture nutrition strategies.

Future innovation will also likely depend on advances in algal biotechnology and industrial cultivation systems. Continued progress in strain selection, heterotrophic fermentation, metabolic engineering, and photobioreactor optimization may improve EPA and DHA productivity while reducing production costs and energy requirements. Integration of algal production systems with carbon capture technologies, wastewater nutrient recovery, and renewable-energy platforms could further strengthen the environmental sustainability of commercial algal-oil production within circular bioeconomy frameworks.

In parallel, increasing application of artificial intelligence, machine learning, and digital aquaculture technologies may improve feed formulation efficiency and real-time nutritional management. Predictive modeling approaches integrating growth performance, environmental parameters, feed conversion efficiency, and omega-3 retention could support the development of adaptive feeding strategies tailored to specific salmonid production systems.

Finally, future investigations should place greater emphasis on long-term commercial validation under realistic farming conditions. Multi-cycle feeding trials evaluating fillet quality, oxidative stability, reproductive success, disease resistance, consumer acceptance, and economic performance remain limited. Greater harmonization of international regulatory frameworks and sustainability certification systems will additionally be important for accelerating broader industrial adoption of algal-derived omega-3 oils within global salmonid aquaculture.

Collectively, these future directions highlight the transition of microalgal oils from alternative lipid ingredients toward strategically important functional components within resilient, climate-adaptive, and nutritionally sustainable salmonid production systems.

10 Conclusion

Microalgal oils have emerged as promising and scientifically validated alternatives to conventional fish oil in salmonid aquaculture. Current evidence demonstrates that algal-derived omega-3 lipids can maintain growth performance, feed efficiency, survival, fillet quality, and tissue EPA and DHA deposition in major salmonid species while simultaneously reducing dependence on finite marine resources and lowering contaminant accumulation in edible tissues. Beyond nutritional replacement, algal oils also influence immune regulation, oxidative stress responses, intestinal health, and molecular pathways associated with metabolic adaptation and environmental resilience. Despite remaining challenges related to production cost, oxidative stability, and large-scale commercial implementation, ongoing advances in algal biotechnology, precision nutrition, and sustainable production systems continue to improve the feasibility of algal-derived omega-3 ingredients. Collectively, the evidence reviewed in this manuscript supports the view that microalgal oils represent more than alternative lipid sources; they are strategically important functional ingredients capable of supporting sustainable salmonid production, preserving seafood nutritional quality, and advancing climate-resilient aquaculture beyond conventional fish oil dependency.

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Footnotes

Edited by: Ana Basto, University of Porto, Portugal

Reviewed by: Arti Kumari, Bihar Agricultural University, India

Vishal Kumar, Lovely Professional University, India