Rhodotorula mucilaginosa effect on Seabream microbiome

The pigmented yeast Rhodotorula mucilaginosa has the potential to improve fish health through its probiotic and antioxidant properties. This study aimed to evaluate the use of lyophilized R. mucilaginosa as an additive for gilthead sea bream (Sparus aurata) diets. Four experimental diets containing different inclusion levels (C:0%, RM1:1%, RM2:2%, RM3:3%) were formulated and tested in a 3-month feeding trial using gilthead sea bream. Each diet was randomly assigned to triplicate groups of ?sh (initial body weight 199.8 ± 1.56g). Fish were hand-fed twice daily at a rate of 1.2% BW. At the end of the trial, the growth indices, blood biochemical parameters, gut gene expression, and microbiome were assessed. Also, the interaction between the host's gut gene expression and microbiome was evaluated. Results indicated that R.mucilaginosa did not significantly affect growth, but it influenced several metabolic and physiological factors. Blood biochemical analysis revealed changes in cholesterol (CHOL) and alkaline phosphatase (ALP) levels, suggesting potential benefits in liver function and lipid metabolism. Gene expression showed upregulation of key genes involved in lipid biosynthesis and metabolism, while microbiome analysis indicated enrichment of beneficial gut bacteria, supporting improved gut health and metabolic regulation. R. mucilaginosa supplementation altered gut microbiota interactions in host fish gene expression that were not observed in the control group, related to potential benefits in immune regulation, and the metabolism of carbohydrates and lipids. These results suggest that R. mucilaginosa inclusion may promote healthier metabolic profiles and enhanced immune responses in gilthead sea bream.