Protective effects of dietary Ocimum basilicum and Thymus vulgaris essential oils on growth performance, immune response, and disease resistance following challenge with Aeromonas hydrophila in Nile Tilapia (Oreochromis niloticus)
摘要
Intensive farming of Nile tilapia (Oreochromis niloticus) heightens susceptibility to infectious diseases, including motile aeromonad septicemia caused by Aeromonas hydrophila, thereby necessitating sustainable alternatives to antibiotics. This study investigated the effects of dietary supplementation with Ocimum basilicum (sweet basil) essential oil (1% w/w) and Thymus vulgaris (thyme) essential oil (0.5% w/w) on growth performance, hematological parameters, serum biochemistry, innate immune responses, cytokine profiles, and resistance to experimental A. hydrophila challenge. A total of 180 juvenile Nile tilapia (initial weight 13.21 ± 0.16 g) were randomly assigned to three dietary treatment groups (three replicates of 20 fish per treatment) and fed for 60 days: (1) basal control diet, (2) basal diet supplemented with 1% O. basilicum essential oil, and (3) basal diet supplemented with 0.5% T. vulgaris essential oil. Fish then received intraperitoneal A. hydrophila challenge (0.1 mL of 1.5 × 108 CFU mL⁻1). Growth, hematological, serum biochemical, and innate immune parameters (lysozyme, nitric oxide, phagocytic index) were assessed at days 30, 60, and 75 (15 days post-challenge). Differential leukocyte counts and cytokine concentrations (TNF-α, IL-1β, IL-6, IL-2, IL-10) were assessed at day 75, and histopathological analysis of hepatic and cephalic kidney tissues was performed to evaluate the protective effects of dietary supplementation against A. hydrophila-induced tissue damage. Both essential oil supplements significantly enhanced growth performance (final body weight and weight gain), hematological indices (hemoglobin concentration and erythrocyte and total leukocyte counts), serum protein profiles (total protein, albumin, and globulin), and innate immune function (lysozyme activity, nitric oxide production, and phagocytic index) compared to the control group (P ≤ 0.05). Notably, the diet supplemented with 1% O. basilicum essential oil produced substantial responses than the diet supplemented with 0.5% T. vulgaris essential oil across several assessed parameters (P ≤ 0.05). Fish fed the O. basilicum-supplemented diet had the highest levels of both pro-inflammatory (TNF-α, IL-1β, IL-6) and anti-inflammatory (IL-10) cytokines, and the lowest overall mortality rate (2.2 ± 2.2%; relative percent survival [RPS] = 96.7 ± 3.3%). The T. vulgaris group had a mortality rate of 13.3 ± 3.9%; RPS = 82.1 ± 6.4%, and the non-supplemented control group had a mortality rate of 77.8 ± 5.9%. Histopathology confirmed markedly diminished renal and hepatic lesions, coupled with increased activation of melanomacrophage centers in both essential oil-supplemented groups. These results suggest that adding 1% O. basilicum essential oil to the diet of Nile tilapia promotes growth, boosts the immune system, and provides greater protection against A. hydrophila infection than adding 0.5% T. vulgaris essential oil. The findings support the potential use of these phytogenic additives as components of health-management strategies in Nile tilapia culture. However, additional studies under commercial production conditions, including dose-optimization, long-term safety assessments, and economic evaluations, are required before practical application can be recommended.