Increasing farming intensification combined with climate-related environmental stressors, including reduced dissolved oxygen and elevated water temperatures, presents major challenges in tilapia cage aquaculture. This commercial field trial evaluated the efficacy of a Bacillus-based direct-fed microbial (DFM) wafer, Sanolife™ PRO-TAB, on the performance of red tilapia (Oreochromis niloticus) during nursery and pre-grow-out stages in floating river cages in Thailand. Fingerlings (initial mean weight 25 g) stocked at 1,600 fish per cage were assigned to control or treatment groups (n = 2 cages per group). PRO-TAB was supplemented daily at 3% of total feed ration over a 34-day period. Supplementation significantly improved all key performance indicators: feed conversion ratio (FCR) improved by 20.7% (1.34 vs. 1.69 in controls), and growth performance increased by 12.6%. Kaplan-Meier survival analysis demonstrated a statistically significant increase in cumulative survival (92.63% in PRO-TAB vs. 79.81% in controls; p < 0.0001), representing a 63.4% reduction in overall mortality. These results demonstrate that Sanolife PRO-TAB substantially improves productivity, growth, and disease resilience under commercial cage culture conditions.