In a groundbreaking study published in the journal Foods, researchers from the Ecological Aquaculture Lab at UC Santa Cruz have introduced an innovative and sustainable solution for aquaculture feed. Their latest development replaces traditional fishmeal in farmed rainbow trout diets with a marine microalgae species, Nannochloropsis sp. QH25, offering a game-changing approach to sustainable seafood production.
A Sustainable Alternative to Fishmeal
The research team has spent years experimenting with new feed formulations, aiming to replace fishmeal—typically derived from wild-caught fish—with a more sustainable ingredient. Their findings reveal that microalgae can completely substitute fishmeal without compromising fish growth, nutritional value, or cost-effectiveness.
This innovation addresses a major challenge in the seafood industry. With global seafood demand surging and wild fish stocks depleting, aquaculture has become a key solution. However, conventional aquaculture relies heavily on fish-derived feed, creating further strain on marine ecosystems. Replacing fishmeal with alternative protein sources like microalgae could significantly reduce this dependency, promoting sustainable fish farming.
Why Microalgae? The Key to Sustainable Fish Nutrition
Aquaculture feeds have evolved to include plant-based ingredients, but completely replacing fishmeal has been difficult due to its high nutritional value, especially its omega-3 fatty acids like DHA, which are essential for human health. Marine microalgae offer a direct oceanic source of these nutrients, making them an ideal replacement for fish-derived feed components.
Microalgae, or phytoplankton, are single-celled organisms that serve as the foundation of oceanic food webs. They naturally produce essential nutrients that accumulate in fish through the marine food chain. By incorporating microalgae directly into fish feed, researchers can maintain these crucial nutrients while eliminating the need for fishmeal.
Breakthrough in Rainbow Trout Feed
The UC Santa Cruz team, led by Assistant Professor Pallab Sarker, has been refining fish-free feed formulations for years. While previous success was achieved with Nile tilapia, replacing fishmeal in carnivorous species like trout and salmon proved more challenging. Initial attempts faced setbacks, as rainbow trout—naturally predatory fish—were reluctant to consume microalgae-based feeds.
To overcome this hurdle, researchers identified key feeding stimulants. They incorporated taurine and lecithin, naturally present in fishmeal, to enhance the aroma and taste of microalgae-based feed. Additionally, they optimized processing techniques, including high-temperature extrusion and improved ingredient mixing, resulting in a more palatable and nutritionally balanced feed.
Successful Results and Future Prospects
A two-month feeding trial involving over 500 rainbow trout confirmed the effectiveness of the new formulations. Fish fed with microalgae-based diets at varying levels (33%, 66%, and 100%) exhibited growth rates comparable to those on conventional fishmeal-based diets. The cost-effectiveness and nutritional value of the resulting fish fillets remained unchanged, demonstrating the viability of microalgae as a fishmeal alternative.
The next step for researchers is to replace fish oil, further advancing the goal of completely fish-free aquafeeds. They also aim to increase the proportion of microalgae in feed to improve fish nutrition, reduce aquaculture’s carbon footprint, and minimize competition with land-based food sources.
The Future of Microalgae in Aquaculture
Marine microalgae have immense potential for transforming the aquaculture industry. However, large-scale production remains a challenge due to high costs. Currently, the most economical approach involves recycling microalgae byproducts from human dietary supplement production. To make microalgae a mainstream aquafeed ingredient, production costs must decrease through technological advancements and industry scaling.
“Microalgae are still expensive due to processing costs, but ongoing research and industry collaboration can drive cost reductions and promote widespread adoption,” explained Sarker. As the global aquaculture sector continues to expand, partnerships between microalgae producers and fish farmers could pave the way for a more sustainable and resilient seafood industry.
With growing interest in sustainable food systems, this research highlights a promising path toward reducing the environmental impact of fish farming while maintaining high-quality nutrition for consumers. The adoption of microalgae-based feeds could be a pivotal step in securing the future of sustainable aquaculture.
More information:
Pallab K. Sarker et al, Towards Sustainable Aquafeeds: Microalgal (Nannochloropsis sp. QH25) Co-Product Biomass Can Fully Replace Fishmeal in the Feeds for Rainbow Trout (Oncorhynchus mykiss), Foods (2025). DOI: 10.3390/foods14050781