<p>Probiotics, including beneficial bacteria and yeasts, are vital for maintaining a healthy gut and overall well-being of animals. Host-derived probiotics may provide a viable alternative to commercial probiotics, positively affecting the growth performance, immune response, and gut microbiome of the Giant Freshwater prawn, <i>Macrobrachium rosenbergii</i>. To explore this, the study was designed with four treatments: two for commercial probiotics (T1 and T2), one for host-derived probiotics (T3), and one control (without probiotics). A total of 264 post-larval prawns (PLs), each with an initial weight of (0.25 ± 0.05) g, were randomly distributed among 12 tanks and fed a commercial diet supplemented with probiotics at a target dosage of 1 × 10⁸ CFU/g for 127 days. Immune-related biochemical parameters and enzyme activities were significantly enhanced in the host-derived probiotic treatment (T3) compared with the control (<i>p</i> &lt; 0.05), whereas commercial probiotics showed only moderate improvements. Microbial community profiling was conducted using an amplicon sequence variant (ASV)-based approach. Alpha-diversity indices tended to be higher in probiotic-fed groups, particularly in T3. Ordination analyses revealed visually distinct but statistically nonsignificant differences in gut microbial community structure among treatments, likely due to limited replication. Differential abundance analysis identified members of the phylum Actinobacteriota as characteristic taxa associated with the host-derived probiotic treatment. Overall, the findings suggest that host-derived probiotics can enhance immune response and influence gut microbial composition in <i>M. rosenbergii</i>. While microbiome-level changes should be interpreted cautiously, the results highlight the potential of host-derived probiotics as a functional dietary strategy for improving prawn health and gut ecosystem stability in aquaculture.</p>