This study delved into the impact of the probiotic and immunostimulant complex, Vimolert®, on the immune response of the Nile tilapia fish challenged with Aeromonas hydrophila. The investigation encompasses an in-depth analysis of hematological and immune parameters within the context of fish diets enriched with Vimolert®. The experimental setup entailed the involvement of 150 Nile tilapia fish, thoughtfully partitioned into five equitable groups. Among these, groups 1 and 2 functioned as control-negative and control-positive entities, respectively. Meanwhile, groups 3, 4, and 5 were subjected to varying doses of Vimolert® (2.5, 3, and 3.5g/ 100g of feed, respectively) as a prophylactic measure. At the culmination of the four-week feeding regimen, the fish in groups 2- 5 encountered a challenge with A. hydrophila. In the initial four weeks of the experiment, groups 3, 4, and 5 witnessed a noteworthy surge in red blood cell (RBC) count and hemoglobin (Hb) concentration, while other hematological parameters like hematocrit (Ht) value, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) remained unchanged. Concurrently, there were substantial elevations in total leukocyte and neutrophil counts across all groups, underscoring a strengthened immune response. Notably, phagocytic percent and phagocytic index exhibited significant enhancements in groups 3, 4, and 5 compared to the control group. After a six-week interval, a slight decrement was observed in RBC count, Hb concentration, and Ht, while MCV exhibited significant augmentation in groups 2, 3, 4, and 5. Lymphocyte and monocyte counts experienced modest increases, while eosinophil and basophil counts remained unaltered. Nevertheless, the six-week period witnessed a highly significant augmentation in all leukocyte subtypes across all groups, with group 4 demonstrating the most substantial increase and group 2 the most restrained. Group 2 displayed a significant decline in phagocytic percent and phagocytic index in comparison to the control group, whereas groups 3, 4, and 5 demonstrated remarkable improvements in these parameters relative to group 2. In summation, this study culminates in the assertion that the probiotic and immunostimulant complex, Vimolert®, at a dosage of 3g/ 100g of feed, stands as an efficacious prophylactic agent against A. hydrophila infection in the Nile tilapia fish. These findings contribute to a deeper understanding of the potential of Vimolert® in fortifying the immune responses of fish and, by extension, elevating their resilience against pathogenic challenges, offering promising implications for aquaculture practices.