Algae have been consumed for millennia in several parts of the world as food, food supplements, and additives, due to their unique organoleptic properties and nutritional and health benefits. Algae are sustainable sources of proteins, minerals, and fiber, with well-balanced essential amino acids, pigments, and fatty acids, among other relevant metabolites for human nutrition. This review covers the historical consumption of algae in Europe, developments in the current European market, challenges when introducing new species to the market, bottlenecks in production technology, consumer acceptance, and legislation. The current algae species that are consumed and commercialized in Europe were investigated, according to their status under the European Union (EU) Novel Food legislation, along with the market perspectives in terms of the current research and development initiatives, while evaluating the interest and potential in the European market. The regular consumption of more than 150 algae species was identified, of which only 20% are approved under the EU Novel Food legislation, which demonstrates that the current legislation is not broad enough and requires an urgent update. Finally, the potential of the European algae market growth was indicated by the analysis of the trends in research, technological advances, and market initiatives to promote algae commercialization and consumption.

Aquaculture has been challenged to find alternative ingredients to develop innovative feed formulations that foster a sustainable future growth. Given the most recent trends in fish feed formulation on the use of alternative protein sources to decrease the dependency of fishmeal, it is fundamental to evaluate the implications of this new paradigm for fish health and welfare. This work intends to comprehensively review the impacts of alternative and novel dietary protein sources on fish gut microbiota and health, stress and immune responses, disease resistance, and antioxidant capacity. The research results indicate that alternative protein sources, such as terrestrial plant proteins, rendered animal by-products, insect meals, micro- and macroalgae, and single cell proteins (e.g., yeasts), may negatively impact gut microbiota and health, thus affecting immune and stress responses. Nevertheless, some of the novel protein sources, such as insects and algae meals, have functional properties and may exert an immunostimulatory activity. Further research on the effects of novel protein sources, beyond growth, is clearly needed. The information gathered here is of utmost importance, in order to develop innovative diets that guarantee the production of healthy fish with high quality standards and optimised welfare conditions, thus contributing to a sustainable growth of the aquaculture industry.

Aims This study used high‐throughput sequencing to evaluate the intestinal microbiome dynamics in rainbow trout (Oncorhynchus mykiss) fed commercial diets supplemented with either pre‐ or probiotics (0·6% mannan‐oligosaccharides and 0·5% Saccharomyces cerevisiae respectively) or the mixture of both. Methods and Results A total of 57 fish whole intestinal mucosa and contents bacterial communities were characterized by high‐throughput sequencing and analysis of the V3–V4 region of the 16S rRNA gene, as well as the relationship between plasma biochemical health indicators and microbiome diversity. This was performed at 7, 14 and 30 days after start feeding functional diets, and microbiome diversity increased when fish fed functional diets after 7 days and it was positively correlated with plasma cholesterol levels. Dominant phyla were, in descending order, Proteobacteria, Firmicutes, Actinobacteria, Acidobacteria, Bacteroidetes and Fusobacteria. However, functional diets reduced the abundance of Gammaproteobacteria to favour abundances of organisms from Firmicutes and Fusobacteria, two phyla with members that confer beneficial effects. A dynamic shift of the microbiome composition was observed with changes after 7 days of feeding and the modulation by functional diets tend to cluster the corresponding groups apart from CTRL group. The core microbiome showed an overall stability with functional diets, except genus such as Escherichia–Shigella that suffered severe reductions on their abundances when feeding any of the functional diets. Conclusions Functional diets based on pre‐ or probiotics dynamically modulate intestinal microbiota of juvenile trout engaging taxonomical abundance shifts that might impact fish physiological performance. Significance and Impact of the Study This study shows for the first time the microbiome modulation dynamics by functional diets based on mannan‐oligosaccharides and S. cerevisiae and their synergy using culture independent high‐throughput sequencing technology, revealing the complexity behind the dietary modulation with functional feeds in aquatic organisms.

This work aimed to evaluate the effects of dietary supplementation with β-glucans extracted from yeast (Saccharomyces cerevisiae) and microalga (Phaeodactylum tricornutum) on gene expression, oxidative stress biomarkers and plasma immune parameters in gilthead seabream (Sparus aurata) juveniles. A practical commercial diet was used as the control (CTRL), and three others based on CTRL were further supplemented with different β-glucan extracts. One was derived from S. cerevisiae (diet MG) and two different extracts of 21% and 37% P. tricornutum-derived β-glucans (defined as Phaeo21 and Phaeo37), to give a final 0.06% β-glucan dietary concentration. Quadruplicate groups of 95 gilthead seabream (initial body weight: 4.1 ± 0.1 g) were fed to satiation three times a day for 8 weeks in a pulse-feeding regimen, with experimental diets intercalated with the CTRL dietary treatment every 2 weeks. After 8 weeks of feeding, all groups showed equal growth performance and no changes were found in plasma innate immune status. Nonetheless, fish groups fed β-glucans supplemented diets showed an improved anti-oxidant status compared to those fed CTRL at both sampling points (i.e., 2 and 8 weeks). The intestinal gene expression analysis highlighted the immunomodulatory role of Phaeo37 diet after 8 weeks, inducing an immune tolerance effect in gilthead seabream intestine, and a general down-regulation of immune-related gene expression. In conclusion, the results suggest that the dietary pulse administration of a P. tricornutum 37% enriched-β-glucans extract might be used as a counter-measure in a context of gut inflammation, due to its immune-tolerant and anti-oxidative effects.