Study finds insect- and algae-based trout feeds match control diets

A new study in Animals reports that practical rainbow trout feeds formulated with insect meal, microalgae-derived omega-3 sources, plant proteins, and aquaculture by-products delivered growth, body composition, nutrient retention, and fillet quality outcomes comparable to a conventional control diet in a feeding trial. The tested formulations included three eco-efficient diets — No-PAP, PAP, and Mix — designed to reduce dependence on traditional marine ingredients while maintaining production performance. The finding fits with a broader body of fish nutrition research showing that insect meals, algae-based ingredients, and by-product protein mixtures can replace a meaningful share of fishmeal and fish oil without materially compromising growth or product quality when formulations are balanced carefully. In juvenile yellowtail, for example, a 6-week Animals trial found that replacing up to 35% of fishmeal protein with shark by-product-based composite mixtures maintained growth and survival, with some diets even improving feed efficiency, although certain formulations lowered EPA and DHA levels. (mdpi.com)

Why it matters: For veterinary and aquaculture professionals, the study adds practical evidence that alternative feed ingredients are moving beyond proof-of-concept and into formulations that could support fish health, performance, and fillet quality at commercial relevance. That matters as producers face continued pressure to reduce fishmeal dependence, manage feed costs, and document sustainability claims. Earlier rainbow trout studies have found similar performance with insect-based diets, while microalgae work suggests omega-3 targets and even feed-cost metrics can be maintained, though inclusion levels and ingredient combinations still need fine-tuning. The yellowtail data add a useful reminder that by-product-based replacements can also work well on growth and efficiency, but fatty-acid quality still needs monitoring when marine ingredients are reduced. (mdpi.com)

What to watch: The next step is whether these eco-efficient formulations hold up in larger commercial trials, with added scrutiny on gut health, welfare, economics, ingredient sourcing, regulatory acceptance across markets, and fillet fatty-acid profiles when by-product mixtures are used more aggressively. (mdpi.com)