Inclusion of algae blend in European seabass diets: Impacts on intestinal histomorphometry and microbiota

The increasing interest in the aquaculture industry and the functional feeds market has brought natural added-value products, such as algae, into the spotlight. Moreover, within the aquaculture community, there is a growing focus on maintaining intestinal health through dietary interventions, as it significantly impacts fish performance. In this study, we evaluated the impact of an algae blend-supplemented feed on the intestinal histomorphometry and microbial communities of European seabass. Our study involved a control group (CTRL) and three blend diets (Blends 2, 4, and 6) with 2%, 4%, and 6% algae inclusion, respectively. The results revealed that blend-fed fish displayed increased muscularis thickness, villi length, and a higher number of acid goblet cells compared to the CTRL group, suggesting that this algae blend can positively affect intestinal motility, nutrient absorption, and mucosal immunity. The microbial composition of the intestine of European seabass showed a robust dominance of Proteobacteria, with varying second-most prevalent phyla among dietary groups. Delftia emerged as the most prevalent genus, indicating the intricate dynamics of the seabass gut microbiota. Although microbial diversity remained relatively stable across groups, the intestine of fish fed the Blend 2 diet exhibited significant alterations in specific bacterial genera compared to the other experimental diets, including Burkholderia, Streptococcus, Acinetobacter, Enterobacter, Corynebacterium, Brevundimonas, Rhizobium, Tepidimonas, Anoxybacillus and Plesiomonas. In summary, our study demonstrates the significant impact of the algae blend on seabass intestinal structure and microbial composition. However, the extent of these effects is closely tied to inclusion levels, and specific bacterial group alterations may not align with changes in intestinal structure, growth, and immune responses. This highlights the importance of employing advanced techniques to comprehensively study the gut microbiota and understand the intricate interactions between intestinal bacterial communities and overall fish performance and health.