Dietary supplementation of Nile tilapia (Oreochromis niloticus) diets with bay laurel (Laurus nobilis): alleviation of oxidative stress and amelioration of immune response, serum biochemistry, and resistance against Aeromonas hydrophila.

Herbal plants can enhance immunity and alleviate oxidative stress in fish. Therefore, the present work was performed to evaluate the effects of bay laurel (Laurus nobilis) on growth, immunity, antioxidant activities, disease resistance, and hematology in Nile tilapia (Oreochromis niloticus). A total of 225 Nile tilapia fingerlings (average weight 15.36 ± 0.04 g) were divided into five treatment groups and fed with bay laurel at 0, 10, 15, 20, and 25 g/kg diet for 90 days. A completely randomized design with three replications was applied. The significantly (p < 0.05) improved weight growth (WG), food conversion ratio (FCR), average daily growth (ADG), protein efficiency ratio (PER), and survival rate were observed in fish fed with bay laurel-supplemented diet at the rate of 15 g/kg. Significantly improved red blood cells (RBCs) count, white blood cells (WBCs), hemoglobin (Hb), and significantly declined alanine aminotransaminase (ALT) and aspartate transaminase (AST) were found in the same diet-fed group. The immune response parameters such as nitro blue tetrazolium (NBT), lysozyme activity, phagocytic activity, total serum protein, serum albumin, serum globulin, and albumin-globulin ratio were found significantly improved at 15 g/kg bay laurel supplemented diet. The improved antioxidant response (catalase, glutathione peroxidase, malondialdehyde, total antioxidant activity) was also observed in the same diet-fed group. Relative percent survival after the fish challenged against Aeromonas hydrophila was significantly (p < 0.05) different. Overall, bay laurel supplementation at a 15 g/kg diet improved the nutritional physiology and immunity and, therefore, could be a potential growth-promoting feed additive for aquaculture development.