
The use of fermented brewer’s spent grain in aquaculture is emerging as a key breakthrough in sustainable fish farming. Brewer’s spent grain, a by-product of the brewing industry, has long been recognised for its nutritional potential, yet its high fibre content and low digestibility have restricted its application in aquafeed.
In recent years, research into solid-state fermentation has demonstrated its ability to enhance the nutritional quality of this new ingredient and other plant-based ones, transforming raw materials into a viable alternative to conventional feed components. However, questions remained about the optimal inclusion levels, metabolic impact, and long-term effects on fish health.
A recent study published in Fishes provides fresh insights into these issues, offering a detailed analysis of the effects of fermented brewer’s spent grain in the diet of European seabass (Dicentrarchus labrax). Led by Tássia Estavão-Rodrigues, the study examines how this novel ingredient improves digestibility, optimizes metabolic efficiency, and reduces oxidative stress, marking a major step forward in the use of agro-industrial by-products in aquaculture.
New Findings Support Greater Inclusion in Aquafeeds
While previous studies demonstrated that fermenting brewer’s spent grain with fungi such as Aspergillus or Rhizopus increased protein content and reduced anti-nutritional factors, there were still doubts as to whether fish could fully utilise these diets without compromising growth and health.
The latest findings reveal that solid-state fermented brewer’s spent grain can be included in seabass diets at levels of up to 20% without negatively affecting performance, a significant development compared to earlier studies. Even more notably, a 10% inclusion of fermented brewer’s spent grain exceeded the performance of the conventional control diet, suggesting not just equivalence but additional benefits beyond simple ingredient substitution.
The study shows that fermented brewer’s spent grain enhances plasma metabolites, particularly glucose, phospholipids, and triglycerides, compared to unfermented raw material. This indicates that fermentation improves nutrient bioavailability, enabling fish to metabolise feed more efficiency. Notably, this research goes further than previous studies, as it establishes a direct link between fermented-treated brewer grain and improved hepatic enzyme activity, reinforcing its role in metabolic regulation.
A Verified Functional Feed Ingredient

While earlier studies hinted at possible antioxidant benefits of fermented raw material, this latest research provides clear evidence that brewer’s spent grain fermented reduces oxidative stress. Fish fed with this novel ingredient exhibited lower lipid peroxidation levels and more stable antioxidant enzyme activity, confirming that brewer’s spent grain solid-state fermented is not only a nutritional feed ingredient but also a functional additive that strengthen fish health and resilience.
These findings are particularly relevant for the aquaculture industry, which faces increasing pressure to reduce reliance on fishmeal and conventional plant-based proteins. Brewer’s spent grain is widely available, and its transformation through fermentation aligns with circular economy principles, offering both environmental and economic benefits.
Several research groups are at the forefront of investing the benefits of fermented brewer’s spent grain in aquaculture. The team led by Helena Peres at the Centre for Marine and Environmental Research (CIIMAR) in Portugal has been pioneering the use of this novel ingredient and has played a crucial role in demonstrating the nutritional and metabolic advantages of solid-state fermented brewer’s spent grain for Europea seabass. Their research has confirmed that fermentation with Aspergillus ibericus significantly enhances digestibility and growth performance.
Beyond Portugal, researchers at the Technical University of Denmark are also exploring ways to process brewer’s spent grain into high-value aquafeed ingredients. Their work focuses on removing anti-nutritional factors and optimizing fermentation techniques, making brewer’s spent grain a viable protein source for fish feed.
These collaborative efforts highlight the growing interest in converting the raw material into a reliable, sustainable feed ingredient, reducing the aquaculture industry’s dependence on conventional protein sources.
The fact that a 10% inclusion of brewer’s spent grain solid-state can surpass the performance of conventional diets suggests that this ingredient is not merely a sustainable alternative but a potential game-changer for aquafeeds.
Recommended references:
- Estevão-Rodrigues, T. et al. (2025). Effect of Solid-Fermented Brewer’s Spent Grain on Growth, Metabolism, and Oxidative Status of European Seabass (Dicentrarchus labrax). Fishes, 10(2), 49. https://doi.org/10.3390/fishes10020049
- Fernandes, H. et al. (2022). Application of Fermented Brewer’s Spent Grain Extract in Plant-Based Diets Improves Pre- and Post-Mortem Oxidative Status of European Seabass (Dicentrarchus labrax). Aquaculture Nutrition, 2022, 2629052. https://doi.org/10.1155/2022/2629052
- Vieira, L. et al. (2023). Solid-State Fermentation as Green Technology to Improve the Use of Plant Feedstuffs as Ingredients in Diets for European Sea Bass (Dicentrarchus labrax) Juveniles. Animals, 13(17), 2692. https://doi.org/10.3390/ani13172692
- Ibarruri, J. et al. (2019). Solid-State Fermentation of Brewer’s Spent Grain Using Rhizopus sp. to Enhance Nutritional Value. Waste and Biomass Valorization, 10, 3687–3700. https://doi.org/10.1007/s12649-019-00654-5
- Ferreira, M. et al. (2024). Fermented Agar By-Product and Sunflower Cake Mixture as Feedstuff for European Seabass (Dicentrarchus labrax). Animal Feed Science and Technology, 315, 116048. https://doi.org/10.1016/j.anifeedsci.2024.116048
- Amaral, D. et al. (2023). Solid-State Fermentation of Plant Feedstuff Mixture Affected the Physiological Responses of European Seabass (Dicentrarchus labrax) Reared at Different Temperatures and Subjected to Salinity Oscillation. Animals, 13(3), 393. https://doi.org/10.3390/ani13030393
- Technical University of Denmark (DTU) Research on Processing Brewer’s Spent Grain for Sustainable Fish Feed