The diet supplemented with raw and hydrolyzed Microchloropsis gaditana and Arthrospira platensis blend modulates intestinal microbiota and metabolomic profiles in Sparus aurata.

The transition toward sustainable aquaculture has prompted the search for alternative feed ingredients that support fish health while reducing dependence on fishmeal. Microalgae such as Microchloropsis gaditana and Arthrospira platensis are rich in bioactive compounds with potential functional benefits. This study evaluated the effects of supplementing gilthead seabream (Sparus aurata) diets with a 10% blend of raw or enzymatically hydrolyzed M. gaditana and A. platensis on intestinal microbiota composition and metabolomic profiles. Over a 41-day feeding trial, fish were fed either a control diet or diets supplemented with raw or hydrolyzed microalgae. Microbial communities were assessed via 16S rRNA gene sequencing, and intestinal metabolites were profiled using UPLC-QTOF and GC-MS. The hydrolyzed microalgae diet induced a marked shift in microbial composition, characterized by a significant increase in Proteobacteria and reduced alpha diversity, particularly in the anterior intestine, whereas the raw diet preserved microbial diversity and promoted the presence of beneficial taxa such as Fusobacteria. Both supplemented diets led to a reduction in inflammation-related metabolites, including 12-keto-leukotriene B4 and 15-keto-prostaglandin E2, and facilitated the accumulation of beneficial long-chain fatty acids, such as oleic and stearic acids. Overall, these findings indicate that dietary inclusion of M. gaditana and A. platensis, particularly in hydrolyzed form, can modulate gut microbiota and intestinal metabolic responses in S. aurata, supporting their potential use as functional and sustainable aquafeed ingredients.