Essential Oil of Bay Laurel (Laurus nobilis) Enhances Growth and Immunity in Cold-Stressed Nile Tilapia (Oreochromis Niloticus).

Bay laurel (Laurus nobilis) essential oil is known for its antimicrobial, anti-inflammatory, and antioxidant properties. This study examined the effects of L. nobilis oil (LN) on Nile tilapia (Oreochromis niloticus) under cold stress conditions (16°C). Tilapia (initial weight, 5.02 ± 0.02 g) were acclimatized to 16°C for 14 days before being fed diets containing 0, 0.5, 1.0, 1.5, 2.0, and 2.5 g/kg LN oil for 84 days. The 1.5 g/kg LN oil group exhibited the highest final body weight and weight gain (p ≤ 0.05), while survival rates peaked at 1 g/kg. Biometric indices and feed efficiency were significantly enhanced, particularly at 1.5 g/kg (p ≤ 0.05). Histological analysis revealed improved intestinal and hepatic structures in LN-supplemented groups, although mild alterations were observed at 2.0 and 2.5 g/kg. Blood biochemical analysis showed increased total protein and reduced cholesterol in supplemented groups. Immune responses, including serum lysozyme activity and bacterial inhibition, were significantly enhanced at 1.5 g/kg or higher (p ≤ 0.05). Antioxidant enzyme activities, including superoxide dismutase (SOD) and catalase (CAT), increased (p ≤ 0.05) with LN oil supplementation, while malondialdehyde (MDA) levels decreased, indicating reduced oxidative stress. Gene expression analysis demonstrated increased insulin-like growth factor 1 and glucose transporter 4 levels with 1.5 g/kg LN oil, and tumor necrosis factor-alpha expression decreased at higher dosages. Dietary LN oil, particularly at 1.5 g/kg, enhances growth, immunity, and antioxidant defense in Nile tilapia under cold stress. Future studies should optimize dosages and explore broader applications across species and conditions.