Microalgae Fully Replace Fishmeal and Fish Oil in Trout Feed

In earlier work, the team substituted a microalgal byproduct, Nannochloropsis oculata, for fishmeal and added taurine — a nutrient also present in fishmeal — plus lecithin. The additions helped fish accept and consume the diet, and growth matched fishmeal-fed fish.

The new study tackled the remaining marine ingredient: fish oil. The team added both oil and whole-cell forms of a second microalga, Schizochytrium, combined with canola oil. The whole-cell form of Schizochytrium performed best, alongside the established Nannochloropsis base.

"This is really groundbreaking," said Pallab Sarker, an associate professor and sustainable aquaculture scientist on the team. "The future of feeding the world should not come at the expense of our ocean, and finding sustainable alternatives is essential to producing more food without depleting the marine resources we depend on."

In plain terms: two algae species, one feed, zero fish ingredients, no measurable growth penalty.

What does this change for feed producers?

Anne Kapuscinski, director of the Coastal Science and Policy Program at UC Santa Cruz and a study author, framed the economic case. Producers growing marine microalgae can control yield stability far better than fleets chasing wild forage fish, she said, while fishmeal and fish oil prices grow more volatile as oceans warm. Replacing ocean-derived nutrients with microalgae would also, in her words, mean "less potential for harm to marine biodiversity."

The economics look plausible for another reason. Microalgae are an "underused byproduct," according to Sarker, recyclable from the manufacture of human food supplements and dyes. Diverting that waste stream into aquafeed would give the byproduct value of its own. Wide-scale reuse of these byproducts is not yet established, so costs remain a constraint — but the team says its feed appears potentially cost-competitive with current products. Microalgae can also grow in saltwater or briny water, so production does not compete with food crops for fresh water.

The one-line takeaway: the feed could undercut fishmeal on both price stability and environmental footprint.

What are the limitations and next steps?

These results come from a controlled laboratory trial with one species, rainbow trout, over roughly two months. The researchers have already run tests at the Mt. Lassen Trout Farm and a California Department of Fish and Wildlife hatchery; those trials showed no statistically significant growth difference between fish on commercial feed and fish on the alternative.

"The next step is to move from promising experimental results toward practical applications," Sarker said. "We need to evaluate these feeds at larger scales, plus other microalgal byproducts."

If larger trials confirm the early findings, fish farming could expand without drawing harder on wild fish stocks. As Sarker put it: "This is more than a new fish feed; it is a step forward, reimagining how we produce food for a global population while protecting the oceans that sustain us."

The bottom line for the industry: watch the scale-up trials — they will decide whether algae feed moves from the lab to the hatchery.