Which Novel Ingredient Should be Considered the “Holy Grail” for Sustainable Production of Finfish Aquafeeds?

The immense production of fishmeal and fish oil is dramatically intensifying the severe state of pelagic fisheries overexploitation. The latter in conjunction with the increasing demand for low-cost protein-rich food supply prompt aquaculture to employ new practice. Several novel dietary ingredients are currently under evaluation for potential incorporation in aquafeeds in an effort to shift the aquaculture sector toward a more sustainable and economic production. The present review aims to summarize the existing findings regarding the effects of studied alternatives to fishmeal and fish oil on the most valuable and commercially produced marine (Sparus aurata and Dicentrarchus labrax) and freshwater (Salmo salar and Oncorhynchus mykiss) finfish species in European aquaculture. Alternative protein sources, including macroalage (marine plants), krill (marine fishery), insects (terrestrial), terrestrial animal by-products (processed/rendered), and single cell ingredient (biotechnology), are discussed for their efficiency in promoting the growth and the welfare of both fry and adult cultured finfish species. Applicability of these ingredients is reviewed in terms of nutrient composition, dietary inclusion level, performance output, digestibility, and health benefits. In addition, a meta-analysis was conducted based on data from peer-reviewed scientific publications in order to assess whether novel ingredients meet the dietary protein (amino acid) and lipid requirements of finfishes. Aquafeed reformulation strategies should ensure the recommended daily nutritional requirements and additionally indicate the meta-analysis alternatives, such as microalgae, which are deficient in essential amino acids. The sustainable expansion of aquaculture is on the horizon, but which novel ingredients may be regarded as the key drivers to its establishment?