Alternative protein sources in aquafeeds for rainbow trout: overview on fillet quality modifications

Aquaculture has been facing the major challenge to answer the growing demand for fish to feed the world population, mitigating its pressure on finite natural resources. Since aquaculture highly depends on marine and vegetable materials as ingredients for aquafeeds, namely fishmeal (FM) and soybean meal (SBM), many studies aimed to design a sustainable and eco-friendly fish production chain by cutting down FM and SBM incorporation rate in aquafeed. Novel ingredients, such as insect meals or poultry by-products, are the most promising strategies for the aquaculture sector. Nevertheless, several impairments of fish fillet quality, such as the decreased content in polyunsaturated fatty acid, are the main weaknesses which need to be minimised while proposing new ingredients for feed formulation. The present trial aimed to compare the use of poultry by-products (P60) and Hermetia illucens larvae meal (H60), as single or in the blend (H10P50), to substitute plant protein in a vegetable-rich based diets (CV) for rainbow trout (Oncorhynchus mykiss). After 27 weeks of the feeding trial, 27 fish for each group were slaughtered and fillet yield, color (lightness, L*; redness index, a*; yellowness index, b*), hardness, and fatty acid (FA) profile of the fish fillets were analysed. A consumer test with 80 people was assessed to evaluate liking and intention of re-consumption. Fillets yield and hardness were unaffected by the dietary treatment. Fillet L* value was significantly higher in H10P50 than CV, being 49.08 and 46.95, respectively. P60 and H60 fillets showed intermediate L* values. Diet did not affect a* and b* values. Noticeably, the formulated diets were able to mitigate the differences in fillet FA profiles, in particular, the addition of animal-derived protein did not increase saturated FAs and the n-3/n-6 ratio was equal to 1.4. Consumers’ liked trout fillets regardless of the dietary treatment, however, the H60 group was described as more fibrous and less juicy than the others. Despite this, 78% of respondents declared their intention to re-consume the product. In conclusion, considering fish fillet quality characteristics, the formulated diets were suitable and valuable alternatives to reduce plant-protein ingredients in feed for rainbow trout. Improving the n-3/n-6 ratio remains a priority to support human health that deserves further investigations.