A new study in Animals shows that fishmeal- and fish oil-free diets can sustain growth in rainbow trout. However, this shift brings new questions about product quality and real sustainability gains.
Researchers from Fondazione Edmund Mach, University of Florence and SPAROS tested multi-source diets using insects, microalgae, microbial proteins, yeasts and animal by-products. Within this context, the aim was to assess whether performance could be maintained without relying on marine ingredients.
The 97-day trial confirmed that removing fishmeal and fish oil does not reduce productive performance. Fish grew from 63 g to 335–353 g, with a feed conversion ratio close to 0.78 and almost no mortality.
Beyond growth, the study also examined fillet quality. Composition remained stable, with 65.8% moisture, 16.3% protein and 12.6% fat, and no clear differences in texture. However, colour emerged as a key variable linked to ingredient choice.
Specifically, diets without processed animal proteins produced more yellow fillets due to xanthophylls. In contrast, diets including these proteins resulted in paler fillets. This shift in colour may affect consumer acceptance, especially in markets that expect a pink or salmon-like appearance.
At the same time, the environmental analysis adds another layer to the discussion. Alternative diets reduced carbon footprint compared to the control, particularly those including processed animal proteins. Even so, these gains were not consistent across all formulations.
In fact, the origin and type of ingredients played a critical role. Microalgae and microbial proteins increased emissions in some cases, contributing up to 20% of total impact. Meanwhile, in the conventional diet, soy protein concentrate remained one of the main contributors.
Taken together, the results show that sustainability in aquaculture is not a simple substitution exercise. Replacing fishmeal is now technically viable, but it creates new trade-offs between performance, environmental impact and product perception.
Reference:
Faccenda, F.; Ciani, E.; Rossi, L.; Vale-Pereira, G.; Secci, G.; Dias, J.; Conceição, L.E.C. (2026).
Practical Aquafeeds Incorporating Insect and Algae Meals Achieve Quality and Growth Standards Comparable to Traditional Feeds in Rainbow Trout (Oncorhynchus mykiss).
Animals, 16(7), 1000. https://doi.org/10.3390/ani16071000
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