The use of probiotics in aquaculture enhances fish growth and sustainability, yet the role of prebiotics like molasses in optimising probiotic efficacy remains underexplored. This study investigated the effects of varying molasses concentrations (0%, 2.5%, 5.0%, and 7.5% v/v) in Sanolife Pro-W probiotic preparations on the growth performance of Nile tilapia (Oreochromis niloticus) juveniles. A completely randomised design was employed, with 180 juveniles (initial weight: 10-15 g) assigned to four treatment groups, each with three replicate 50-L tanks, over three weeks at TANLAPIA Company Ltd., Bagamoyo, Tanzania. Growth parameters (weight gain, feed conversion ratio, specific growth rate) were measured weekly, and water quality was maintained within optimal ranges (temperature 26-30°C, DO >5 mg/L). One-way ANOVA revealed significant differences in mean weights among groups (3, 8) =79.08, p<0.001), with the 5.0% molasses group exhibiting the highest average weight across time points. Trend analysis indicated consistent superiority of the 5.0% group, while the 7.5% group showed a weight decline at the final measurement. These findings suggest that 5.0% molasses optimises the efficacy of Bacillus-based probiotics, enhancing tilapia growth. However, weight gain trends suggest the 5.0% molasses group had the highest SGR, reflecting faster growth, and likely a better FCR due to enhanced nutrient utilization. The 5.0% concentration likely optimized Bacillus activity, improving gut health and feed efficiency, as supported by (Verschuere et al., 2000).This cost-effective approach could improve aquaculture profitability and sustainability in Tanzania’s blue economy. Further research is needed to elucidate the mechanisms underlying molasses-probiotic interactions and long-term impacts on fish health and water quality