Modulatory Effects of Water Extract from Eleutherine americana on Intestinal Health: Insights from Growth, Morphology, Microbiota and Metabolomics in Plectropomus leopardus

This study evaluated dietary Eleutherine americana water extract (EAW, 0 [NC], 1 [LD], 5 [MD], and 10 [HD] mL/kg) in 480 juvenile leopard coral grouper (Plectropomus leopardus; initial body weight, 11.72 ± 0.34 g) over 8 weeks, with four replicate tanks of 30 fish per treatment. EAW did not significantly improve growth performance, but survival was higher in MD and HD than in NC (p < 0.05). Histological observations indicated more intact mucosal folds, greater crypt depth, and higher goblet-cell counts. Metabolomic analysis showed lower carnitine levels and higher phospholipid and prostaglandin metabolites, with annotated differences in bile acid biosynthesis, amino acid metabolism, and carbon metabolism pathways. Intestinal microbiota profiles showed lower relative abundances of Pseudomonadota and Basidiomycota in EAW groups, lower Actinomycetota in LD and MD, and higher Bacteroidota and Bacillota in MD. At the genus level, Bradyrhizobium, Microbacterium, and Sphingobium abundances were lower, and Afipia abundance was higher, in EAW groups. Functional profiles varied in carbohydrate, amino acid, and lipid metabolism categories. Microbiota–metabolite correlation networks identified Pseudomonadota, Actinomycetota, hexosylceramides, and carnitines as highly connected features. Network pharmacology identified pdgfra, pdgfrb, and sirt1 as candidate targets of the major EAW components eleutherol, eleutherin, and isoeleutherin. The survival and intestinal findings support further evaluation of EAW as a feed additive for intestinal health in leopard coral grouper.