Effects of dietary β-cyclodextrin-encapsulated lemongrass essential oil (βCD-LGEO) on gut microbiota, intestinal health, and disease resistance of saline tilapia hybrid (Oreochromis spilurus × Oreochromis niloticus) fry.

The effects of dietary β-cyclodextrin-encapsulated lemongrass essential oil (βCD-LGEO) were investigated in the early fry stage of saline-tolerant UPV SpiN tilapia hybrid (Oreochromis spilurus × Oreochromis niloticus), focusing on growth performance, resistance to Aeromonas hydrophila, gut health, innate inflammatory responses, and gut microbiota composition. The fish were fed diets containing 0, 0.5, 1, or 2% βCD-LGEO for 30 days. Growth did not differ significantly between control and treated groups. However, survival following A. hydrophila infection increased from 50% in the control group to 90% in fish receiving 0.5% βCD-LGEO. The treatment also reduced culturable gut bacteria by tenfold relative to the control. Consequently, the intestines of fish from the control and 0.5% βCD-LGEO groups were subjected to gene expression analysis of inflammatory cytokines, histomorphometry, and 16S rRNA gene sequencing. Expression of TNF-α, IL-6, and IL-1β in the 0.5% βCD-LGEO group was reduced to 18%, 62%, and 28% of control levels, respectively, while villus length was significantly increased. Dietary supplementation also altered gut microbial composition with differential abundance analysis identifying significantly enriched and reduced taxa in treated fish, whereas predicted microbial functional profiles remained unchanged. These findings demonstrate that dietary βCD-LGEO at 0.5% promotes intestinal health and enhances resistance to A. hydrophila infection in UPV SpiN tilapia fry. These beneficial effects were associated with a reduced intestinal bacterial load, suppression of inflammatory responses, and modulation of gut microbial communities, supporting the potential of βCD-LGEO as a sustainable phytogenic alternative to antibiotics in tilapia aquaculture.