Effects of dietary inclusion of crude or hydrolyzed Arthrospira platensis on intestinal microbiota in gilthead seabream (Sparus aurata) fry

Fish feed has traditionally relied on fishmeal and fish oil, but the industry is seeking sustainable alternatives, such as microalgae and cyanobacteria. This study evaluates the effects of dietary inclusion of crude or hydrolyzed Arthrospira platensis biomass on the growth and intestinal microbiota in gilthead seabream (Sparus aurata) fry. A 45-day feeding trial was conducted using four experimental diets containing 5% and 10% (w/w) crude or hydrolyzed A. platensis, alongside a control diet without cyanobacteria. None of the dietary treatments significantly affected fish size or growth. Diets including 5% crude or hydrolyzed biomass did not alter alpha or beta diversity, while the inclusion of 10% crude biomass significantly reduced alpha diversity and induced notable shifts in major ASVs compared to control fish. The 10% crude biomass diet increased the relative abundance of Ochrobactrum sp., Lactococcus sp., and Staphylococcus sciuri, while decreasing Vibrio sp. and Pelomonas aquapure. Despite these microbiota changes, fish fed the 10% crude biomass diet exhibited similar productive parameters to the control group, suggesting that this diet may promote a more beneficial gut microbiota without compromising growth. This approach could help reduce the use of fishmeal and fish oil in starter feeds while maintaining fish growth performance.