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Enhancing Fish Fillets with Black Soldier Fly Meal: Species Matters
Black Soldier Fly (Hermetia illucens) larvae meal (BSFM) is gaining traction as a sustainable substitute for fishmeal in many aquafeeds. A recent meta-analysis of 30 peer-reviewed studies in Journal of Insects as Food and Feed dissects how BSFM impacts fillet quality across key farmed fish species like carp, trout, seabream, and salmon. (ivysci.com) This kind of species-specific approach is crucial: what works for freshwater species may leave marine types wanting more.
Carp and Trout Benefit Most in Fillet Composition
Common Carp (Cyprinus carpio)
Carp fillets reflect some of the strongest positive effects from BSFM substitution:
- Higher protein content and lower fat levels without detriment to moisture or ash content. (mispeces.com)
- Significant shifts in fatty acid composition are minimal in terms of long-chain omega-3s, meaning carp can leverage BSFM without sacrificing critical nutritional features. Moisture and ash remain stable under typical inclusion rates. (brill.com)
Rainbow Trout (Oncorhynchus mykiss)
Trout seem to get a mixed bag of gains and trade-offs when fed BSFM:
- Visual improvements: Fillet appearance tends toward higher lightness (L values), which could influence consumer perception. (ivysci.com)
- Lipids shift: Saturated fatty acids (SFA) and omega-6 polyunsaturated fatty acids (n-6 PUFA) rise. Total fat often increases. However, health-centric omega-3s (EPA/DHA) tend to decline. (ivysci.com)
Marine Species Show More Limits: Seabream & Salmon
Gilthead Seabream (Sparus aurata)
Seabream, being marine, seem less forgiving of high BSFM levels:
- Protein and ash content of fillets tends to drop; same with EPA, an important omega-3. (brill.com)
- Fat content generally goes up, but the imbalance created—more n-6 PUFA vs fewer n-3—can undermine nutritional quality. (brill.com)
Interestingly, a study feeding seabream diets replacing ~10% fishmeal with partially defatted BSFM found that proximate composition (protein, moisture, ash), fillet colour and pH didn’t change much at that inclusion level. EPA/DHA were similarly stable—though some sensory traits of raw fillets shifted. (pmc.ncbi.nlm.nih.gov)
Atlantic Salmon (Salmo salar)
For salmon, critical for its fatty acid profile, BSFM introduces more subtle trade-offs:
- Fillet protein and moisture often decline; lipid content goes up; monounsaturated fatty acids (MUFA) tend to decrease. (ivysci.com)
- However, in a full‐production‐cycle trial with sea cages, using up to 10% BSFM did not significantly alter long-chain omega-3s (EPA/DHA). (sciencedirect.com)
- Sensory issues emerge at higher inclusion, especially around 10%, including perceptions of rancidity and bitterness—though changes in raw fillet appearance and basic composition were small. (sciencedirect.com)
What Drives These Differences? Key Moderators
Several factors modulate how BSFM affects fillet quality:
- Inclusion rate: Low to moderate rates (5–10%) tend to minimize negative outcomes, especially for marine fish. Higher rates make shifts in fatty acid profiles more likely. (brill.com)
- BSFM processing: Use of partially defatted larvae and defatting protocols can influence both protein/lipid content and downstream fillet traits. (pmc.ncbi.nlm.nih.gov)
- Trial duration & scale: Studies spanning whole production cycles in real farming conditions (e.g. sea cages for salmon) differ from short-term feeding trials—cumulative effects, adaptive responses, and feed‐fish interactions all play a role. (sciencedirect.com)
- Species metabolism & lipid handling: Marine fish typically rely more on dietary sources of omega-3s because they convert precursors less efficiently than many freshwater species. When BSFM lacks EPA/DHA or when n-6 fatty acids dominate, imbalance ensues. (brill.com)
Practical Implications for Feed Strategy and Fish Farming
For BSF farmers, feed formulators, and aquaculture operations, these insights translate into actionable shifts:
- Begin with species-specific protocols: Trout and carp can tolerate (and sometimes thrive with) higher replacement levels of fishmeal with BSFM. Marine species like seabream and salmon are more sensitive—lower substitution and supplementation are safer.
- Balance fatty acid profile intentionally: When BSFM replaces fishmeal or plant protein, ensure inclusion of sources rich in EPA/DHA (e.g., microalgae, fish oil) to maintain nutritional value, especially for marine-typed species.
- Use processed BSFM smartly: Partially defatted meal helps reduce high saturated fat content and limit unwanted lipid accumulation in fillets.
- Pilot on full cycles: Implement inclusion trials across the full production cycle to catch effects that short trials might miss—texture, flavour, shelf life, market perception.
- Monitor sensory quality: Taste, odor, texture are just as important as proximate composition. Even if nutrient content looks good, consumer rejection due to “off” flavours can cost more than feed savings.
Where the Research Still Needs Work
- There’s a need for more studies that explore how substrate for larval rearing affects BSFM’s own fatty acid profile— can diets rich in omega-3 precursors shift the insect’s lipid content?
- More consumer sensory panels run blind and with trained tasters, particularly focusing on cooked fillet flavour, texture, juiciness, and appearance under high BSFM levels.
- Longitudinal studies that track changes across multiple generations or broodstock condition under BSFM diets to see if adaptation improves outcomes.
- Economic modelling to assess feed cost vs. gains in sustainability and nutrient value—are savings on fishmeal offset by supplementation or product quality loss?
With these findings, BSFM is more than just a buzzword—it’s a nuanced tool. The newest meta-analytic evidence makes clear that what works brilliantly for carp or trout may need refinement before it’s equally effective for seabream or salmon. In every case, thoughtful feed design, inclusion thresholds, and attention to fatty acids will shape whether BSFM delivers what it promises: sustainability and fillet quality.
