Alternative trout feeds match traditional diets in growth trial

CURRENT BRIEF VERSION: Researchers reported that practical rainbow trout feeds built around insect meal, microalgae, single-cell ingredients, selected plant proteins, and aquaculture by-products matched a conventional diet on growth and overall fillet quality in a 97-day trial, even when fishmeal and fish oil were removed. The work, published in Animals on March 27, 2026, tested four extruded diets, including a conventional control and three alternative formulations labeled No-PAP, PAP, and Mix. Across treatments, trout grew from about 63 g to roughly 335–353 g, feed conversion stayed near 0.78, and mortality was minimal, suggesting these lower-marine-ingredient formulations can perform at commercially relevant levels. The result also fits a broader aquafeed trend beyond trout: in juvenile yellowtail, a separate Animals study found that replacing up to 35% of fishmeal protein with composite shark by-product-based mixtures maintained growth and survival over 6 weeks, with some formulations even improving feed efficiency, though certain diets lowered EPA and DHA levels. (mispeces.com)

Why it matters: For veterinary and aquaculture professionals, the study adds to a growing body of evidence that fishmeal- and fish oil-sparing diets can support salmonid performance without obvious penalties in body composition or core quality metrics. That matters as aquaculture scales: FAO said in June 2024 that aquaculture surpassed capture fisheries as the main producer of aquatic animals for the first time, increasing pressure to find sustainable feed ingredients. The paper also fits within an established European regulatory pathway, where processed insect protein and certain non-ruminant processed animal proteins are permitted in aquaculture feeds under specific conditions. Still, the trade-offs aren’t gone. Coverage of the new paper highlighted shifts in fillet and pellet color, a reminder that market acceptance and product presentation may become the next bottlenecks even when growth performance holds. And the yellowtail data add another caution: by-product proteins can preserve growth while still altering nutrient profiles, including key long-chain omega-3s. (fao.org)

What to watch: Expect follow-up work to focus less on whether trout can grow on these diets and more on cost, ingredient availability, life-cycle sustainability, pigmentation, fatty acid retention, and whether pet parents and seafood buyers accept fish raised on feeds with more insects, algae, and by-product proteins. (mispeces.com)