ISSUE FOCUS 76 FEED & ADDITIVE MAGAZINE August 2025 CHOOSING THE RIGHT INGREDIENT All the mentioned single-cell organisms, among others, demonstrate how flexible and useful they are as ingredients in aquaculture feed. However, treating these ingredients as if they belong to the same category would be a mistake, as there are important differences among them. When approached from a 'beyond protein' perspective, the pathogen-associated molecular patterns (PAMPs) found in yeast and bacteria become particularly appealing. For instance, yeast contains beta-glucans in its cell wall, while bacteria contain lipopolysaccharides (LPS) in their membranes. As the name suggests, PAMPs are molecules associated with pathogens that can interact with components of the immune system to activate the innate immune response. When PAMPs are used within studied dosage ranges, they can act as natural immunological enhancers in fish.11 As for microalgae, one of their strongest advantages is their ability to provide a balanced fatty acid profile for fish, since there are few alternatives aside from fishmeal and fish oil that can do this. It is also worth mentioning that there is a vast variety of microalgae species with different nutritional compositions, something that could be applied to yeast and bacteria through strain selection and cultivation optimization. However, outside niche markets such as aquarium fish, the use of microalgae products is still quite limited due to price. Another interesting point is that many of these ingredients tend to lower the omega-3 content in fish fillets. However, freshwater fish have a limited capacity to produce long-chain omega-3 fatty acids themselves, so feeding them well-studied, balanced diets can help compensate for this reduction. For example, a study by Ruiz et al. (2023) found that replacing 100% fishmeal with Uniprotein® (15% inclusion) did not disrupt the long-chain omega-3 polyunsaturated fatty acid profile of rainbow trout fillet. Despite complete fishmeal replacement, no significant differences were observed in fillet levels of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), or total long-chain omega-3 polyunsaturated fatty acids (Σ n-3 PUFA). This demonstrates that well-formulated diets can maintain essential fatty acid profiles in freshwater fish (Figure 2). Figure 2. Omega-3 levels in rainbow trout fillet with varying Uniprotein® (UP) inclusion levels (Data from Ruiz et al., 2023) 0% UP 3.75% UP 7.5% UP ns EPA DHA Σ n-3 PUFA 11.25% UP 180 160 140 120 100 80 60 40 20 0 µg fatty acid/mg lipid Omega-3 levels in rainbow trout fillet with varying Uniprotein (UP) inclusion levels 15% UP
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