World Aquaculture Magazine - June 2020

68 JUNE 2020 • WORLD AQUACULTURE • WWW.WA S.ORG The nutritional characteristics of BSF are highly plastic and dependent on characteristics of the growth substrate. In this regard, rearing BSF larvae can be enriched with desirable omega-3 fatty acids if reared on a substrate based on organic by- products containing desirable omega-3 fatty acids. This is the framework in which the Nutrifish project is focusing its research activity. Nutrifish is a three-year, Italy-based research project, founded by Cariverona Foundation in 2017, aiming to investigate the use of insect meal as a novel and sustainable ingredient for aquafeed formulation. The approach is to start with results obtained with a laboratory experimental model like zebrafish and then apply in a field setting with a commercial species like sturgeon. The first project step was to identify an environmental- friendly BSF growth substrate among those by-products which production is rising with the increasing food demand and unsustainable food production practices. In this regard, Nutrifish focused its attention on recycling coffee silverskin, the waste product of coffee roasting. It is a waste with widespread production worldwide, rich in bioactive compounds and characterized by antioxidant and potential probiotic properties. To address one of the most critical aspects of the nutritional profile of BSF, represented by low PUFA content, the growth substrate was enriched with several percentages (w/w) of the microalga Schizochytrium sp. (Alghitaly S.R.L.) to improve the fatty acid profile of BSF. Marine microalgae have medium to high levels of good-quality protein with high omega-3 and omega-6 PUFA content, making them ideal, ecologically-sound ingredients for improvement of BSF growth substrate. A 10 percent addition of microalgae to the growth substrate was the best compromise between costs and nutritional improvement of the insect biomass. After this important step, enriched BSF prepupae were produced in large quantities for incorporation into five experimental diets with 0, 25, 50, 75 and 100 percent BSF inclusion with respect to FM (Fig. 1). The enrichment procedure of the insect biomass caused an increasing trend in dietary PUFA content. Thus, the enrichment method represented an innovative approach to enrich an agricultural byproduct (coffee silverskin) and bioconvert it into a valuable ingredient biomass for aquafeed. Test diets were administered to fish to study the biological responses of fish. The first fish trial was performed in an aquatic experimental model organism, the zebrafish Danio rerio , from larval phase to adulthood, to select the best BSF-based diet (Fig. 2). Zebrafish represents an ideal organism to better understand fish physiological responses to new ingredients. In this case, a comprehensive multidisciplinary study was applied that integrated biometric, histological, gas chromatographic, microbiological, spectroscopic, molecular and behavioural analyses. Zebrafish growth was positively affected by increasing inclusion levels of enriched BSF prepupae meal in the diets at larval and juvenile stages, although there was no effect in adults. A 50 percent BSF meal inclusion was the best compromise between fish growth, welfare, fillet quality and sustainability. Laboratory analyses revealed that 75 and 100 percent replacement of FMwith BSF meal caused a stress response in fish leading to a reduction of fish welfare, lipid accumulation in the liver (steatosis) and a strong reduction of the PUFA content of fish fillets. BSF meal inclusion level higher that 50 percent negatively affects both fish welfare and the potential health benefits of fish consumption. The Nutrifish project also aimed to test these new diets directly on a commercial species. For that reason, the diet characterized by 50 percent of FM substitution with BSF meal was selected for a feeding trial at a commercial-farm scale with juvenile Siberian sturgeon Acipenser baerii to elucidate fish biological responses and understand possible implications on human health benefits (Fig. 3). The sturgeon feeding trial was performed in an aquaponics system (MjEnergy, Treia, Italy; Fig. 4). In light of the circular economy concept, combining farmed fish and plant production in a cost-efficient and environmental-friendly way represents an additional important step for the development of a sustainable aquaculture. The choice of an aquaponic system represented an additional important step in Nutrifish project in light of a future zero-waste generation development. Specifically, the fish trials performed on sturgeon represent an example of how aquaculture could be implemented with the re-use of by-products (the substitution of FM and FO with more sustainable and eco-friendly ingredients — insects) while sustaining the production of quality food (fish and plants) and reducing FIGURE 2. Adult zebrafish. Photo: Matteo Zarantoniello. FIGURE 3. Juvenile sturgeon. Photo: Sergio Ciriaco.

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