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- 04/21/2021

Rainbow Trout (Oncorhynchus mykiss) Skin as Potential n-3 Fatty Acid Source

AgroFOOD Industry Hi Tech

Omega-3 fatty acids, as food science has long documented, are an important ally of our health. These polyunsaturated fatty acids help maintain certain metabolic functions and resolve inflammatory processes of various kinds. The human body only synthesises a small proportion of them, which is why a diet containing, for example, fish or fish products in general, is needed to meet our needs.

New findings in this field come from a study on rainbow trout skin, published in Waste and Biomass Valorization by the Aquaculture research group of the Department of Agricultural, Food, Environmental and Forestry Sciences and Technologies (Dagri) of the University of Florence, in collaboration with the University of Udine.

The study was conducted as part of the SUSHIN (SUstainable fiSH feeds INnovative ingredients) Project, funded by Ager (AGER2-SUSHIN Cod 2016-0112). The team discovered that rainbow trout skin contains a higher percentage of omega-3 than the fish fillets themselves and could be re-evaluated for food purposes.

World health authorities recommend that adults consume about 500 mg per day of omega-3, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA): the equivalent of 3.5 g per week. This amount is generally associated with the consumption of about 2-3 portions of 100 g of fish.

Many species of fish are unable to produce EPA and DHA fatty acids from scratch and therefore have to take them into their diet and store them in their tissues. About 60 per cent of the total amount of fish products produced for human consumption comes from aquaculture, which in turn depends on natural resources for the supply of the noblest feed ingredients, fishmeal and fish oil, the main source of omega-3 in the diet of farmed fish.

Over the last 30 years, due to the depletion of natural fish stocks, ingredients of marine origin have been greatly reduced and replaced with protein sources (flours) and oils of vegetable origin. This change in feed has meant that the omega-3 content of farmed fish has declined over time: in the near future, not only will we have to cope with the demand for food of animal origin (especially fish) from a growing world population, but we will also end up with food of lower nutritional quality.

To increase the supply of EPA and DHA, the way forward seems to be to make the most of by-products and prevent food waste. The aim of this study was to characterise the fatty acid profile of rainbow trout (Oncorhynchus mykiss) skin fed with alternative protein sources (larvae meal from the insect Hermetia illucens).

Trout skin is a valuable source of omega-3: the average omega-3 content found in it amounts to 25% of total fatty acids, compared to 15% in fillets from the same animals. Most importantly, this percentage of omega-3 tends to remain constant in the skin, regardless of the diet fed to the animals.

So we need to review our eating habits and value this ‘non-noble’ but extremely rich part of the fish, to avoid throwing essential nutrients such as fatty acids in the bin, as well as the daily work of those committed to increasing the sustainability of the aquaculture sector.