Dietary lemongrass essential oil, growth and gut bacterial communities of red tilapia: An exploratory eight-week trial

An eight-week feeding trial evaluated the effects of dietary lemongrass ( Cymbopogon citratus ) essential oil (LEO) on growth and gut bacterial communities of red tilapia ( Oreochromis sp. ). One hundred twenty fish were assigned to 12 independent 70-L tanks by initial weight strata, with 10 fish per tank and three replicate tanks per dietary treatment. A commercial tilapia diet was supplemented with nominal LEO concentrations of 0, 200, 300, or 400 mg/kg; all diets, including the control, received 100 mL absolute ethanol/kg feed as the carrier. Fish were weighed individually, and tank means were used as the experimental observations for growth analyses. Permutation ANOVA detected no dietary effect on initial body weight, final body weight, weight gain, or specific growth rate (all p≥0.743). Analysis of covariance of final tank weight, adjusted for initial tank weight, showed no significant treatment effect (p=0.784). Midgut digesta and mucosal material from three fish per tank were pooled to produce one sample per experimental unit for 16S rRNA gene amplicon sequencing. After standardization to 21,356 reads per sample, none of the evaluated alpha-diversity indices differed significantly among diets (Kruskal–Wallis p=0.070–0.589). Omnibus PERMANOVA indicated differences in bacterial-community composition based on Bray–Curtis (pseudo-F=2.615, p=0.002) and Jaccard distances (pseudo-F=1.939, p<0.001). However, no pairwise comparison remained significant after false-discovery-rate adjustment, and dispersion differed among treatments for the Jaccard metric (PERMDISP p=0.044). Under the conditions of this study, nominal dietary LEO supplementation (200–400 mg LEO/kg feed) did not affect red tilapia growth. The observed community-level bacterial patterns should be considered exploratory and require confirmation in larger trials with chemically verified diets, greater tank-level replication, and measurements of feed intake and feed utilization.