Using Black Soldier Fly Larvae Meal as a Functional Additive in Aquafeeds Rather than a Primary Protein Source

Why Rethink BSFLM’s Role in Aquaculture Diets

Aquaculture producers are constantly seeking feed ingredients that balance sustainability, nutrition, and economics. Fishmeal—long considered essential—faces supply limitations, high cost, and environmental burden. Black soldier fly larvae meal (BSFLM) has emerged as a promising alternative due to its rich protein content, presence of bioactives, and relatively lower carbon footprint. Yet, the latest research indicates that using BSFLM not as a wholesale protein replacement but as a functional feed additive—in smaller, strategic quantities—may deliver superior health outcomes and better cost-effectiveness.

A functional additive in this context refers to ingredients included at lower inclusion levels not for primary nutrition, but to provide specific physiological benefits—antioxidant support, immune enhancement, gut health promotion, etc.—beyond merely filling the protein quota.

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The Research That’s Shifting Perceptions

Recent trials across multiple species reveal a trend: moderate BSFLM inclusion (often 10–30%) can enhance growth, bolster immune defenses, and improve antioxidant capacity; but higher substitutions (around 50% or more) often lead to adverse effects.

Study Highlights

• Hybrid Grouper (Juvenile, 56-Day Trial): Diets with 10% or 30% BSFLM replacing fishmeal showed solid growth performance and immune enzyme activity. The 30% inclusion seemed optimal overall. But at 50% substitution, growth declined, oxidative stress rose, and gut-health markers shifted negatively. mdpi.com{:rel=“nofollow”}
• Southern Catfish (8-Week Feeding): Replacement levels of 30% and 50% improved antioxidant capacity and growth metrics. Yet muscle texture changed, and while gut morphology remained intact, findings suggest that moderate substitution (around 30–40%) maintains health balance better. mdpi.com{:rel=“nofollow”}
• Rainbow Trout Under High Soybean Meal Diets: Adding just 2.5–5% BSFLM—whole-body or defatted—to soybean-heavy feeds improved immune response, survival following bacterial challenge, and gut morphology. The results were strongest in groups with these low additive levels. pubmed.ncbi.nlm.nih.gov{:rel=“nofollow”}
• Golden Pompano (Juvenile): Replacing 25% of fishmeal improved feed intake, liver health, and lipid metabolism. Moving to 50% replacement reduced growth performance, pointing to a ceiling for safe inclusion. sciencedirect.com{:rel=“nofollow”}

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Deep Dive: What Happens at Different Inclusion Levels

BSFLM Inclusion Level	Observed Benefits	Risks / Trade-Offs
Low (≈2.5–10%)	Enhances immune gene expression, improves gut integrity, increases disease resistance. Especially effective when the rest of diet stresses the fish (e.g. high soy). pubmed.ncbi.nlm.nih.gov{:rel=“nofollow”}	Minimal changes in growth performance; may not offset cost if diet already optimized.
Moderate (≈25–30%)	Strong growth, protein efficiency, antioxidant enzyme activity; favorable lipid metabolism in species like hybrid grouper. mdpi.com{:rel=“nofollow”}	Slight risk of altering muscle texture or lipid profile; excess saturated fats possible if using full-fat BSFLM.
High (≈50%+ replacement)	Some species still show good growth; promotes gut microbiota shifts—sometimes to beneficial taxa. mdpi.com{:rel=“nofollow”}	Elevated oxidative stress, immune burden, reduced growth, possible negative impacts on health markers. Often negative to muscle texture and feed appeal.

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Underlying Bioactive Mechanisms: What Makes BSFLM More Than Just Protein

Besides its protein content, BSFLM brings several functional components that activate beneficial biological responses:

• Antimicrobial Peptides (AMPs) & Chitin: These contribute to innate immunity by disrupting pathogens and supporting gut barrier integrity. mdpi.com{:rel=“nofollow”}
• Fatty Acids including Lauric Acid: Medium-chain fatty acids, notably lauric acid, are known for antimicrobial and immune-modulating effects. In rainbow trout diets, lauric acid from BSFL increased in tissues in proportion to inclusion. pubmed.ncbi.nlm.nih.gov{:rel=“nofollow”}
• Antioxidants & Defensive Enzyme Activity: Elements like T-AOC (total antioxidant capacity), SOD (superoxide dismutase), and others often spike at moderate inclusion levels, helping fish buffer oxidative stress. mdpi.com{:rel=“nofollow”}
• Positive Microbiota Shifts: Moderate to high inclusion shifts gut flora—often increasing beneficial bacterial groups like Clostridia—important for gut health and immune priming. mdpi.com{:rel=“nofollow”}

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Balancing Taglines: Recommendations by Species and Purpose

Here’s a species-wise guideline based on current data, focusing on additive use vs. protein replacement:

• Rainbow Trout: 2.5–5% BSFLM (whole or defatted) works well in high-soy diets—boosts immune response and gut health without jeopardizing growth. pubmed.ncbi.nlm.nih.gov{:rel=“nofollow”}
• Hybrid Grouper: Best outcomes seen when 10–30% of fishmeal replaced by BSFLM; 30% yields strong immune, antioxidant, and growth responses. 50% comes with trade-offs. mdpi.com{:rel=“nofollow”}
• Southern Catfish: Though 50% replacement boosted growth in trials, taking into account texture and immune balance suggests keeping substitution in the 30–40% range if health markers and consumer product quality are priorities. mdpi.com{:rel=“nofollow”}
• Golden Pompano: A 25% replacement is the sweet spot. Beyond that, performance and health aspects show diminishing returns or even negative effects. sciencedirect.com{:rel=“nofollow”}

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Practical Feed Formulation Tips

To make the most of BSFLM as a functional additive without risking downsides:

1. Choose the Right Formulation (Full-fat vs. Defatted): Full-fat variants bring more lipids and energy but also risk lipid overload; defatted forms help manage fat content. pubmed.ncbi.nlm.nih.gov{:rel=“nofollow”}
2. Match Substrate Quality: Larvae fed on diverse waste streams with rich nutrient inputs tend to produce meal with better amino acid and fatty acid (e.g., EPA/DHA) profiles. Starchy or low-quality substrate can reduce functionality. pmc.ncbi.nlm.nih.gov{:rel=“nofollow”}
3. Monitor Health Markers: Especially immune enzymes (lysozyme, AKP), oxidative stress indicators (CAT, SOD, MDA), gut morphology, and microbiota composition. These tend to tell early if inclusion is tipping into the harmful range.
4. Stage Matters: Juveniles are often more sensitive. Adult or grow-out stages may tolerate higher substitutions—but functional additive benefits are most visible during early growth or under dietary stress.
5. Cost vs. Benefit: Low inclusion (additive level) is less expensive and can reduce disease costs or improve meat quality. High protein replacement needs to factor in cost of BSFLM, potential risks, and product quality implications.

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Implications for Producers, Feed Mills, and BSF Farms

• BSF Producers: Marketing BSFLM as more than just a protein substitute—highlighting immune benefits, antioxidant potential, and functional health traits—can differentiate products. Invest in processing methods (defatting, clean substrate feeding) to improve bioactive profiles.

• Feed Manufacturers: Instead of reformulating completely toward insect protein, blending BSFLM into existing feeds—particularly those with known stressors or where immune resilience is key—may be more viable. Create “health boosters” versions of feeds.

• Farmers: Trials on farm with small percentages to test local responses make sense. Also, gathering data on disease incidence, feed conversion, and product quality can help quantify value.

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