Dietary tea tree (Melaleucae Aetheroleum) oil fortifies growth, biochemical, immune-antioxidant trait, gene function, tissue reaction, and Aeromonas sobria resistance in Nile tilapia (Oreochromis niloticus)

Abstract

The current study had aimed to assess the long-term dietary supplementation with Melaleucae aetheroleum, tea tree essential oil (TTO). The impact on growth performance, biochemical indices, immune function, oxidant/antioxidant activity, gene expression, histopathology, and resistance against Aeromonas sobria in Nile tilapia (Oreochromis niloticus) was investigated. Four groups (with five replicates; G1 (control group, G2, G3, and G4) of Nile tilapia received diets enriched with TTO (doses of 0.0, 0.5, 1.0, and 2.0 mL/kg diet) for 60 days, then fish were challenged by A. sobria. Outcomes indicated an extensive elevation in growth metrics (final body weight, weight gain, SGR, feed intake and fish body protein). Similarly, the total blood protein, albumin, total globulin levels, Serum complement-3 levels, lysozyme activity, immunoglobulin M (IgM), nitric oxide, and phagocytic activity were significantly enhanced in all treatments, notably in the 2.0 mL TTO/kg fed groups compared to the control. Lower levels of urea, creatinine, AST, ALP, ALT, cortisol, glucose, triglycerides, cholesterol and body crude lipids were observed in the fish that were fed a 2.0 mL TTO/kg diet. Supplementing TTO at 2.0-mL /kg diet revealed the best results for elevating CAT, SOD, and GSH activities plus declining MDA value in hepatic homogenate. Additionally, dietary 2.0-mL TTO/kg showed the best outcomes for the intestinal morphometry plus maintaining the histological picture in spleen and liver. Concurrently, fish that were fed a 2.0 mL TTO/kg diet exhibited a substantial upregulation of TNF-α, IL-1β, IL-10, TFG-β, IFN-γ and BCL-2 genes in the liver, while, caspase-3, and BAX were downregulated. Furthermore, TTO-enriched diets enhanced the relative percentage survival post-A. sobria challenge plus enhanced the clinical picture in a dose-dependent manner. Taken together, the findings revealed that long-term exposure to dietary TTO fortified the physiological performance, oxidant/anti-oxidant stability, immune function, gene expression, histological picture, and resistance of Nile tilapia against A. sobria.

Keywords: Aeromonas sobria; Melaleucae Aetheroleum oil; Growth trait; Histo-biochemical indices; Nile tilapia.

Fig. 1

Effect of TTO dietary supplementation on innate immune parameters of O. niloticus for 60 days. Data expressed as mean ± SE, N = 10 for each group. Columns bearing different letters are significantly different at p < 0.001

Fig. 2

Effect of TTO dietary supplementation on antioxidant biomarkers in the liver tissues of O. niloticus. Data expressed as mean ± SE, N = 10 for each group. Columns bearing different letters aresignificantly different at p < 0.001

Fig. 3

Effect of TTO dietary supplementation for 60 days on mRNA expression of tumor necrosis factor alpha (tnf-α), transforming growth factor-beta (TGF-β), interferon- gamma (IFN-γ), interleukin 10 (IL-10), and interleukin 1 beta (i1- β) genes in the liver of Oreochromis niloticus. Data expressed as mean ± SE, N = 10 for each group. Each bar carrying different letters (a, b, and c) was significantly different at p < 0.001

Fig. 4

Effect of TTO dietary supplementation for 60 days on mRNA expression of caspase-3, apoptosis regulator BAX, BCL-2-like protein in the liver of Oreochromis niloticus. Data expressed as mean ± SE, N = 10 for each group. Each bar carrying different letters (a, b, and c) was significantly different at p < 0.001

Fig. 5

Representative photomicrograph of H&E-stained sections from liver (Scale bar 100 μm) showing: A normal histological structures of hepatic cells (stars) around a central vein and groups of pancreatic acini (arrows) around branches of the portal vein (PV) in all groups (A, B, C, D). Melanomacrophage centers adjacent to pancreatic acini particularly in control group (arrowhead) (A)

Fig. 6

Representative photomicrograph of H&E-stained sections from spleen (Scale bar 100 μm) showing: A: Preserved structures of red pulps, white pulps and sinusoids in all groups (A, B, C, D) with numerous foci of melanomacrophage deposits (arrows) around ellipsoids arterioles in group fed 0 ml TTO /kg diet (A). Gradually decrease melanomacrophage centers (arrows) at group received 0.5 ml TTO /kg diet (B) followed by group received 1.0 ml TTO /kg diet (C) then group received 2.0 ml TTO /kg diet (D)

Fig. 7

Representative photomicrograph of H&E-stained sections from intestine (Scale bar 100 μm) showing: normal configurations of simple columnar enterocytes lining mucosal villi (V), submucosal layer and muscular layer (M) in all groups (A, B, C, D)

Fig. 8

Intestine morphometry of O. niloticus, fed with diets enriched with different levels of TTO for 60 days. Bars assigned by different letters are significantly different at P < 0.001

Fig. 9

Clinical observation of O. niloticus after 14 days of A. sobria challenge, following a 60-day diet supplemented with TTO showing: control fish which received 0 ml TTo/Kg exhibited sever body hemorrhages (star) (A) and fin rot (arrow head), and skin ulcers (red arrows) (B). Fish received 0.5 ml TTo/kg diet exhibited mild fin rot (blue arrow) (C). Fish received 1.0 ml TTo/kg diet exhibited mild fin hemorrhage (D). Fish received 2.0 ml TTo/kg diet exhibited normal appearance (E) and (F)