The Path to Sustainable Aquaculture
What if the future of the world’s seafood supply isn't found in the depths of the ocean, but in the bins of a corn mill or the by-products of a poultry farm? For decades, the aquaculture industry has wrestled with a paradox: to farm enough fish to feed a growing planet, we must harvest massive amounts of wild "feeder" fish to create fishmeal, a process that strains marine ecosystems.
Shattering an Old Assumption
A new study on juvenile gilthead seabream (Sparus aurata) has shattered the assumption that we must choose between ocean health and fish growth.
For the average consumer, this means the "sustainable" fish on the dinner plate may soon be raised on a diet that is more efficient and creates less environmental waste than current commercial standards.
The Study at a Glance
In a controlled 80-day trial, scientists monitored 324 fish across four distinct dietary regimes.
The Tested Diets
Circular Economy Ingredients
Researchers discovered that by-products from terrestrial plants and processed animal proteins (PAP) don't just match the performance of traditional fishmeal—they actually exceed it.
- Plant By-products: Included corn gluten and rapeseed meal.
- Processed Animal Proteins (PAP): Included poultry and porcine blood meal.
Emergent Proteins
This group was fed a diet composed of so-called "trendy" alternative proteins.
- Examples: Ingredients from insects and microalgae.
Commercial Control
This group was fed a diet designed to mimic current commercial standards using fishmeal.
Performance Results: A Clear Winner
The results for circular-economy ingredients were striking, while emergent proteins showed significant drawbacks.
Superior Performance of By-products
Fish fed diets of plant by-products and PAP achieved outstanding metrics:
- Feed Conversion Ratio (FCR): 1.3 – Significantly outperforming the emergent proteins.
- Metabolic Efficiency:
- Plant-based group showed protein retention of 28.6%, compared to 23.1% in the control.
- This high efficiency led to reduced environmental waste.
- Environmental Impact: Nitrogen fecal loss—a major driver of water pollution—plummeted to just 86 mg N/kg/day in the plant group.
The Struggles of "Trendy" Proteins
Despite the hype, the fish in the "EMERG" group fed insects and algae struggled:
- Poor Feed Efficiency: FCR climbed to a sluggish 2.0.
- Low Digestibility: Protein digestibility hovered at roughly 70%, compared to over 90% in other groups.
- Biological Toll: The diet weakened the fish's gut barriers, with intestinal health measurements dropping sharply.
Understanding the Results
The research team provided analysis for the divergent outcomes.
Why Did By-products Excel?
The "boring" leftovers from existing food chains (wheat germ, poultry meal) proved to be highly efficient and digestible, creating less waste.
Why Did Emergent Proteins Falter?
The poor performance might be attributed to:
- High Chitin Content: Present in locust and mealworm ingredients.
- Anti-nutritional Factors: These may irritate the digestive tract at high concentrations.
- A "Crowding" Effect: Too many new proteins introduced at once.
A Note on Data: The authors caution that "analytical problems" during whole-body fish content analysis mean some retention data required careful interpretation. Furthermore, because the emergent diet blended ingredients, they cannot yet pinpoint which specific component caused the setback.
Key Conclusion
Ultimately, the path to sustainable aquaculture appears to lie in leveraging the "boring" leftovers of existing food chains rather than making a radical jump to insects. The authors suggest emergent proteins still require significant optimization before they are ready for large-scale commercial use.
Based on: Aragão, C., Cabano, M., Colen, R., Fuentes, J. and Dias, J., 2020. Alternative formulations for gilthead seabream diets: Towards a more sustainable production. Aquaculture Nutrition 26: 444–455.