Investigating the effects of wild olive Olea europaea leaf extract on growth, body composition, digestive enzyme activity, hematological parameters, and immune function in Nile Tilapia

Objective: This study investigated the effects of supplementing Nile Tilapia Oreochromis niloticus diets with wild olive Olea europaea leaf extract (WLE) on growth performance, digestive enzymes, and antioxidant and immunological parameters. Methods: Wild olive leaf extract was added at different concentrations (WLE 0.0 [control], 1.0, 1.5, and 2.0%) and fed to triplicate fish groups for 12 weeks. At the end of the trial period, growth performance, body composition, digestive enzyme activities, and hematological, biochemical, antioxidant, and immunological parameters were evaluated. Result: According to the results, fish that were fed with WLE 1.5% and WLE 2.0% exhibited significantly improved weight gain, specific growth rate, and feed intake. The feed conversion ratio (FCR) was significantly reduced in fish supplied with WLE 1.5% and WLE 2.0%. Additionally, weight gain and FCR showed significance at both the linear and quadratic levels, as indicated by polynomial contrasts. However, the experimental diets did not impact fish body composition, digestive enzyme activity, or survival rate. Fish that received WLE 1.5% and WLE 2.0% showed significantly higher levels of white blood cells, red blood cells, hemoglobin, and hematocrit compared with the WLE 1.0% and control groups. Moreover, significant enhancements were observed in serum parameters, including total protein, albumin, globulin, lysozyme, catalase, superoxide dismutase, and total immunoglobulins, for the WLE 1.5% and WLE 2.0% groups compared with the control. Fish that were fed WLE 1.5% exhibited the lowest serum cortisol level. Conclusion: In conclusion, experimental diets with WLE levels of 1.5% and 2.0% effectively enhanced both the growth and immunological parameters of Nile Tilapia.