Traditional fish farming practices can exert pressure on wild fish populations. Researchers are exploring innovative solutions, and one promising approach is the development of sustainable fish feeds made from plant-based ingredients.
An article published by scientists from INRAE investigated the potential of plant-based diets for rainbow trout, a popular species in aquaculture. The study aimed to investigate the combined effect of using a blend of alternative ingredients (yeast, microalgae, and insects) and selective breeding on the performance and metabolism of rainbow trout.
Challenges and solutions for sustainable fish feeding
While plant-based ingredients form the basis of many fish feeds, they have not yet reached the performance levels necessary for fish farms to be profitable. Researchers are exploring ways to improve fish feeding by:
- Selecting high-quality plant proteins: This ensures that fish receive essential nutrients.
- Introducing alternative ingredients: These can include plant products, animal by-products, or single-celled ingredients like microalgae and yeast. These add valuable nutrients and mimic natural fish food.
- Genetic selection of fish: Breeding fish that thrive on plant-based diets can improve overall performance and profitability.
Single-cell proteins and potential for insects
Single-cell proteins such as microalgae and yeast show promise as supplements in plant-based diets. They provide proteins and lipids that carnivorous fish need, and some even help restore intestinal health affected by plant-based foods. While yeast production is well established, microalgae production is still in its early stages.
Another interesting alternative comes from insects. Insect larvae, rich in proteins and suitable for fish needs, are being produced on a pilot and even industrial scale. These options are promising for mimicking natural fish food and promoting intestinal health.
Vegetable protein for fish?
Most research has focused on individual alternative ingredients. The study proposes combining them (creating a “blend”) to better meet fish nutritional needs by leveraging the complementary benefits of each component.
The researchers conducted the following experiments:
- Experiment 1: The researchers tested two diets supplemented with blends with different levels of protein purification from plant-based ingredients in unselected trout lines. They compared these diets with their unsupplemented counterparts and with a commercial fish meal-based diet.
- Experiment 2: Refined diets supplemented with a blend were then tested in both a trout line selected for plant-based diets and an unselected control line.
Success with supplemental ingredients
The first experiment revealed that while the plant-based diet alone supported fish growth, it did affect their ability to convert food into usable energy. However, when this diet was supplemented with the blend of insects, microalgae, and yeast, the fish’s feed conversion ratio improved, suggesting that the blend effectively compensated for any deficiencies in the purely plant-based diet.
The key finding? Trout fed these diets showed growth performance similar to those fed a commercial fish meal-based diet. This suggests that the supplements addressed any nutritional deficiencies in the purely plant-based feed.
Selective breeding
Another strategy is to select fish that perform well on plant-based diets over generations. Studies have demonstrated a genetic basis for adaptation to plant-based diets in several fish species. This approach has produced fish lines that outperform unselected lines when fed plant-based diets.
The second experiment introduced another interesting element: genetic selection. The researchers bred a new rainbow trout line specifically to thrive on plant-based diets.
The results were promising! This selected line showed better growth performance when fed both the plant-based diet and the plant-based diet supplemented with the blend of insects and yeast, compared to an unselected line.
Metabolic clues: unlocking the power of adaptation
Metabolomics, a relatively new approach in fish nutrition, provides a comprehensive view of the metabolic changes fish undergo when fed plant-based diets. This approach reveals alterations in protein, lipid, and carbohydrate metabolism. However, metabolomics also shows that genetic selection can offset some of these changes, leading to better performance.
The study employed metabolomics to analyze fish plasma. This analysis revealed some interesting insights. Fish fed plant-based diets, with or without the mixed supplement, showed a stable plasma composition, characterized by amino acid accumulation and glucose depletion compared to those fed commercial diets.
In the selected line, feeding with the mixed supplement and commercial diets led to changes in specific metabolites such as inositol, ethanol, and methanol, compared to the unselected line. These changes suggest a potential role of the intestinal microbiome in diet adaptation. Furthermore, alterations in the content of a metabolite called glycine-betaine in fish fed the mixed supplement with the selected line point to their enhanced ability to adapt to these alternative ingredients.
Potential for rainbow trout aquaculture
This study offers promising insights:
- Blends enhance performance: Supplementation with the blend of alternative ingredients helped restore fish growth performance affected by plant-based diets.
- Selected lines thrive on plant-based diets: Trout lines bred for plant-based diets showed better performance on these diets with supplementation of the blend.
- Metabolic insights: Metabolomics provided valuable data on metabolic changes induced by plant-based diets and the potential role of mixed supplementation in mitigating these changes.
Conclusion
The study paves the way for the development of sustainable and efficient fish feeds. By combining plant-based ingredients with carefully selected alternative ingredients and selective breeding, researchers are creating a future where we can enjoy healthy fish. Researchers continue to investigate the metabolic consequences of these combined approaches, leading to even more sustainable aquaculture practices.
In the same vein, by reducing reliance on fish meal derived from wild fish populations, these advancements can contribute to healthier oceans and a safer food supply for future generations.
The study was funded by the FUI NINAqua (New Ingredients for New Aquaculture Foods) project and MetaboHUB. Simon Roques was funded by “Phileo by Lesaffre” and the ANRT.
Contact
Benoit Fauconneau
INRAE, Univ. Pau & Pays Adour, E2S UPPA, Nutrition, Métabolisme et Aquaculture
UMR 1419, 64310, Saint Pée sur Nivelle, France
Email: benoit.fauconneau@gmail.com
Reference (open access)
Roques, S., Deborde, C., Médale, F., Lefevre, F., Bugeon, J., Labbé, L., Marchand, Y., Moing, A., & Fauconneau, B. (2023). New alternative ingredients and genetic selection are the next game changers in rainbow trout nutrition: A metabolomics appraisal. Scientific Reports, 13(1), 1-16. https://doi.org/10.1038/s41598-023-46809-2
