This research aimed to assess the impact of integrating synbiotic (A-Pro Aqua®, SYN; 0.05 and 0.1%) and hydrolyzed yeast extract (Nutri Yeast-Aq®, HYE; 0.05 and 0.1%) as a factorial experiment 2×2 in a completel randomized design in the diet on growth performance, hemato-immunulogical responses, and digestive enzyme activities of Nile tilapia (Oreochromis niloticus) fry with intial weight 4 ± 0.2 g for 63 days. Three hundred fish was stocked in fifteen 120-L glass containers (20 fish per each unit) and fed with five diets containing control diet, 0.05% synbiotic + 0.1% yeast, 0.05% synbiotic + 0.05% yeast, 0.1% synbiotic + 0.1% yeast, and 0.1% synbiotic + 0.05% yeast. The findings indicated that elevated SYN and HYE levels significantly (P<0.05) increased final weight, specific growth rate, volountary feed intake, survival rate, protein productive value, and protein efficiency ratio. Additionally, higher SYN and HYE levels resulted in a significant decrease in feed conversion ratio and hepatosomatic index (P<0.05), while the activities of digestive enzymes such as protease, lipase, and amylase were considerably increased (P<0.05). The synergistic application of SYN and HYE in the diet markedly enhanced alternative complement activity and triiodothyronine, immunoglubolin, and lysozyme concentrations in the plasma of test fish (P<0.05). Moreover, the dietary supplementation SYN and HYE significantly elevated high-density lipoprotein concentation in the plasma of test fish, while concurrently reducing low-density lipoprotein, very low-density lipoprotein, and triglycerides concentrations (P<0.05). In summary, based on the growth parameters and hemato-immunological responses, dietary supplementation with 0.1% SYN in conjunction with 0.1% HYE was recommended.

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