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Aquaculture is a growing wide industry, that until now and in the future represents a sector with enormous potential. Despite that, it is still correlated with environmental issues and ambiental impacts. For several years, both the scientific community and the industry have been working together to make this sector increasingly sustainable and resilient. This doctoral thesis deals with the study and valorisation of alternative ingredients chosen for their nutritional characteristics and potential, with the final aim of giving new inputs to aquaculture to become more sustainable. In particular, this study was focused on: -Evaluation of green technologies applied to production of microalgae biomass. Renewable energy sources, such as geothermal, can reduce the environmental impact of aquafeed production. - The use of by-products from fishery and aquaculture in order to replace fish meal fish oil and soybean meal with microalgae. -Evaluate the effect of experimental diets on different life stages of a commercial species widely distributed in the Mediterranean Sea, European Seabass. - Among two Mediterranean species considered, Meagre is an emerging species, considered a valid substitute for the most widespread commercial species such as Gilthead Seabream and European Seabass. Emerging species are a very powerful tool to reduce pressure on those species already heavily bred. - Organic diets were tested on an emerging species, relating both the sustainability of organic diets and the sustainability of emerging species.

The recent fast development of the microalgae-related biotechnologies has enabled the availability of sustainable and nutrients-rich raw materials to be used as substitution of conventional sources in aquafeed formulation. However the cost of energy of the photobioreactors used to produce these microorganisms still constrained their wider inclusion into aquafeed compounds. By exploiting industrial waste outputs, Nannochloropsis sp. and Spirulina sp. were produced and utilised to formulate two experimental enrichments (LM1 and LM2). During a 60 days trial, their efficacy have been tested as Artemia metanauplii enrichments in the diet of European seabass (Dicentrarchus labrax) larvae, in comparison to a commercial control. Larvae were fed with isonitrogenous and isolipidic dietary treatments. Each dietary treatment presented a specific profile for the long chain polyunsaturated fatty acids ARA, DHA and EPA. Ratio of DHA/EPA in enriched Artemia of 4:1 as in the case of LM1 and LM2 in the presence of 1.4% of ARA (as a % on total fatty acid) guaranteed equal results to the control which displayed a ratio of DHA/EPA of 2:1 with 2.2% of ARA. No significant effects of the dietary treatments were detected in final survival, growth performance and incidence of skeletal anomalies. Regarding oxidative status, larvae fed with LM2 enrichment presented lower catalase activity than control larvae with no signs of oxidative damage, suggesting a potential antioxidant effect of LM2. The present study contributes to expanding the existing literature on successful utilisation of microalgae and cyanobacteria, used to produce valuable nutrients, in a perspective of circular nutrients economy