This study aimed to evaluate the supplementation of peppermint essential oil (Mentha piperita; PEO) in diets for juvenile Nile tilapia (Oreochromis niloticus). A feeding experiment with diets containing graded levels (0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 g kg⁻¹) of PEO was carried out with fish of 0.58 ± 0.08 g. The inclusion of graded levels of PEO in the diet improved the weight gain (0.52 g kg⁻¹), feed intake (0.51 g kg⁻¹), and feed conversion (0.51 g kg⁻¹) of juvenile Nile tilapia in a quadratic pattern. Increasing levels of PEO also led to a linear decrease in body lipid content. The gut activity of the digestive enzymes amylase (0.54 g kg⁻¹) and protease (0.39 g kg⁻¹) increased quadratically, whereas lipase activity increased linearly. PEO increased the activity of the antioxidant enzymes catalase (CAT; 0.52 g kg⁻¹) and superoxide dismutase (SOD; 0.58 g kg⁻¹) while reducing the production of malonaldehyde (MDA; 0.40 g kg⁻¹) and nitric oxide (NO; 0.63 g kg⁻¹) in the liver. The results of this study provide evidence of the beneficial effects of PEO on the growth and health of Nile tilapia and recommend a dose of 0.6 g kg⁻¹ as the optimal level of supplementation.

Objective: The continuous use of antibiotics in aquaculture is increasingly discouraged, making natural antimicrobials such as dietary acidifiers and essential oils more attractive alternatives. However, the underlying mechanisms of dietary acidifiers and cinnamaldehyde on oxidative stress and gut bacteriome of Nile Tilapia Oreochromis niloticus remain poorly understood. The purpose of this study was to examine the growth performance, plasma biochemistry, antioxidant status, intestinal digestive enzyme activities, apparent digestibility coefficients, short-chain fatty acid production, histomorphometry, and bacteriome of Nile Tilapia that were fed diets that were supplemented with organic acids and cinnamaldehyde. Methods: Fish (n = 252; weight = 6.4 ± 0.6 g [mean ± SD]) were distributed into three groups. The first group was fed a basal diet (351.8 g/kg, crude protein) without organic acids or cinnamaldehyde supplementation (control [CON]), and the second and third groups were fed with the basal diet supplemented with either butyric acid (1 g/kg; BUT) or a blend of lactic acid, formic acid, and cinnamaldehyde (1 g/kg; LFC), respectively. Each group consisted of four replicates of 21 fish per aquarium. The fish were distributed into 12 aquaria of 60 L each in a recirculating aquaculture system and hand-fed six times daily for 8 weeks. Results: The fish that were fed with the BUT diet showed a trend toward higher body weight gain (+9%) and significantly higher (P = 0.037) whole-body ash (+10%) than those in the CON group. There were no significant differences in plasma biochemical responses between experimental groups (P > 0.05). The activity of the antioxidant enzymes superoxide dismutase and glutathione-S-transferase tended to be higher, whereas lipid peroxidation, assessed through malondialdehyde concentration, was lower (P = 0.032) in the fish that were fed with the LFC diet than those that were fed with the other diets. The activity of amylase (P = 0.012) and total proteases (P = 0.024) were higher in the fish from the LFC group, whereas the apparent digestibility coefficients of dry matter (P < 0.001), gross energy (P < 0.001), and crude protein (P = 0.003) were greater for fish that were fed with the BUT and LFC diets relative to those that were fed with the CON diet. Intestinal pH and short-chain fatty acid production were not different between treatment groups (P < 0.05). Relative to the fish in the CON group, the fish in the LFC group showed enhanced villi height (+60%; P = 0.008) and villi height-to-width ratio (+78%; P < 0.001). Bacteria of the phylum Firmicutes was the most prevalent in digesta across all the experimental groups. Notably, the fish in the BUT group exhibited higher abundance of Cetobacterium sp. and Roumboustia sp., whereas the fish that were fed with the BUT and LFC diets exhibited reduced (P < 0.05) abundance of Staphylococcus sp. in the fish gut. Conclusions: The combined supplementation of lactic acid, formic acid, and cinnamaldehyde markedly enhanced intestinal histomorphometry, as well as promoting beneficial bacterial abundance in the gut of Nile Tilapia. This synergistic blend shows a sustainable potential alternative to chemotherapeutics for in Nile Tilapia farming.