Adding an essential oil blend to the diet of juvenile Nile tilapia improves growth and alters the gut microbiota

In aquaculture, essential oils are considered promising supplements that can improve productive performance and modulate the fish's microbiota. Here we investigate how a blend of essential oils (carvacrol + thymol + cinnamaldehyde acid) affects the productive performance and the intestinal microbiota of juvenile Nile tilapia (Oreochromis niloticus, Thai strain). All fish were randomly distributed into 20 multifilament tanks (10-mm mesh and 2.4 m3 capacity). The experimental design comprised four treatments and five repetitions, with 20 individuals per experimental unit, for 60 days. Four diets were evaluated with increasing levels of essential oils (control and 3.3, 6.7, and 10 g kg−1 diet). Supplementation with 3.3 g kg−1 of essential oils improved growth performance compared to the control group. However, no differences were detected among the essential oil-supplemented groups (6.7 and 10 g kg−1). Survival was not different among the four groups. Using a Linear Response Plateau (LRP) model, we calculated maximum levels of 3.4, 3.5, 3.5 and 3.2 g kg−1 of the essential oils blend for final weight, weight gain, daily weight gain, and feed conversion, respectively. Verrucomicrobia, Firmicutes, Bacteroidetes, and Proteobacteria accounted for a high proportion of the species observed in tilapia's gut microbiota in the control and essential oil-supplemented groups. In both treatments, Candidatus xiphinematobacter (Verrucomicrobia) and Cetobacterium (Fusobacteria) were most predominant at the genus level. Cetobacterium somerae and Lactobacillus zeae were the most abundant species. At the species level, the Shannon index diversity value was higher in the control group than in the essential oil-supplemented groups (P = 0.046719; t = 2.0586). The bacterial community beta diversity analysis revealed an effect of diet on the tilapia's gut microbiota, demonstrating a distinct grouping among treatments. Linear discriminant analysis (LDA) associated with effect size (LEfSe) identified that microbiota's differential abundance was significant when comparing the control group and the 3.3 g kg−1 essential oil-supplemented group. The genera Candidatus xiphinematobacter, Staphylococcus, Caldilinea, and Synechococcus were more abundant in the microbiota of essential oil-fed juvenile Nile tilapia the control group. Pseudomonas, Acinetobacter, Enterococcus, and Lactobacillus were more predominant in the microbiota of fish from the control group. In conclusion, dietary the carvacrol + thymol + cinnamaldehyde acid blend (3.3 g kg−1) increased the growth performance and modulated the gut microbiota of juvenile Nile tilapia.