Fishmeal-free diets work in rainbow trout, but raise new challenges in fillet colour and sustainability

Italy, 26 March 2026 | Additionally, the use of alternative raw materials in aquaculture may shift environmental impact rather than reduce it

Furikake de Porto Muiños

A recent study published in Animals shows that formulating diets without fishmeal and fish oil can maintain rainbow trout growth, but requires closer attention to fillet sensory quality and the real emissions associated with certain ingredients.

Researchers from Fondazione Edmund Mach, the University of Florence and SPAROS evaluated multi-source diets based on insects, microalgae, microbial proteins, yeast and animal and fish by-products. The 97-day trial confirmed that replacing marine ingredients does not compromise productive performance.

Fish grew from an initial weight of 63 g to between 335 and 353 g, with a stable feed conversion ratio around 0.78 and negligible mortality.

In terms of product quality, fillet composition remained consistent (65.8% moisture, 16.3% protein and 12.6% fat), with no significant differences in texture.

However, fillet colour varied: diets without processed animal proteins produced a more yellow hue due to xanthophyll pigments, while diets including these proteins resulted in paler fillets. This shift, although not affecting nutritional value, may influence consumer acceptance in markets where a pink colour is preferred.

From an environmental perspective, alternative diets reduced carbon footprint compared to the control, particularly those based on processed animal proteins.

However, impact strongly depended on ingredient origin and production systems. Microalgae and microbial proteins, for instance, can increase emissions, accounting for up to 20% of total impact in some formulations. In contrast, soybean protein concentrate was a major contributor in the conventional diet.

The study highlights that sustainability in aquaculture is not linear. Replacing fishmeal is now technically feasible, but the next challenge lies in balancing performance, real environmental impact and consumer 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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