The aim of the study was to determine the effect of different levels of BioAcid Ultra on growth performance, survival, enzymatic activity, hematological and biochemical parameters of fingerlings rainbow trout. For this purpose, 900 fish were stocked in three treatments at the Concrete pools and fed 4 times a day by 0.1% and 0.2% of BioAcid Ultra (T1 and T2) for 60 days. After 60 days feeding on the experimental diets, there were no significant difference (P>0.05) was observed in survival of fish. Groups of fish which were fed diet supplemented with 0.1% and 0.2% Bio Acid Ultra displayed improved (P<0.05) growth performance, including GBM and SGR. No significant differencein enzymatic activity (Alkaline Phosphatase (ALP), Alanine aminotranferase (ALT) and Asparatate aminotransferase (AST)) and hematological parameters (Red blood cells (RBCs), white blood cells (WBCs), hemoglobin (Hb) and Hematocrit (Hct)) was observed between T1, T2 and control group (P>0.05). No significant difference (P>0.05) in serum Glucose, Triglyceride and TP was observed in treatments and control group. The results of the present study showed a significant (P<0.05) decrease in Globulin in T1, whereas serum albumin was higher in T1 when compare with control group (P>0.05). In the present study, the best performance of fish in terms of growth performance in fingerlings rainbow trout, was recorded at organic acids at a 0.1% dose.