A research team at the University of California, Santa Cruz, has developed a new rainbow trout feed formulation using microalgae sourced from human dietary supplement byproducts. The study, recently published in Foods, suggests that microalgae could one day serve as a cost-effective alternative to fishmeal derived from wild-caught fish.

In a two-month growth trial with more than 500 trout, researchers tested diets where fishmeal was replaced with the marine microalgal species Nannochloropsis sp. QH25 at levels of 33%, 66%, and 100%. Trout fed the experimental diets grew just as well as those on conventional feed, and their nutritional value for human consumption remained comparable.

Previous attempts to replace fishmeal in carnivorous fish diets had limited success, as trout rejected the taste of algae-based formulations. This time, the team improved palatability by adding taurine and lecithin as flavor and scent enhancers, along with updated processing techniques. The trout readily accepted the feed.

“Microalgae offer enormous potential to reduce aquaculture’s reliance on wild fisheries,” said lead author and assistant professor Pallab Sarker. “The challenge now is scaling production and driving down costs so the industry can take advantage of this resource.”

Sarker noted that while microalgae remain expensive to produce, their high omega-3 content and proven performance in trials provide strong motivation for continued investment and innovation in algae production.