The present study was carried out to determine the antibacterial effect of Streptococcus faecium isolated from the gut of freshwater fish Cyprinus carpio cummunis on Cirrhinus mrigala against Aeromonas hydrophila. The freshwater fish Cyprinus carpio cummunis was collected from Dal lake, Srinagar, Jammu & Kashmir. A total of 6 bacteria were isolated from the above collected fish intestine. The antibacterial activity of the isolated strains against Aeromonas hydrophila was screened by agar well diffusion method. Among the 6 strains, the best antibacterial activity was observed as 17mm in MC5 strain. This strains was identified as Streptococcus faecium by 16s rRNA sequencing. The S. faecium strain was supplemented with pellet feed at three different concentrations such as, 100, 250 and 500 mg per 100g feed. Then it was fed to Cirrhinus mrigala for 60 days and the growth performance such as weight gain, SGR, FCR was analyzed and observed good results. After feeding experiment, it was challenged with Aeromonas hydrophila and the mortality rate was observed daily up to14 days. The mortality of experimental groups were significantly (P< 0.05) decreased with increasing the concentration of probiotic strains than the control group. During the challenge experiment, the immunological parameters such as blood parameters, prophenoloxidase, respiratory burst activity and superoxide dismutase activity was analyzed at an every 7 days intervals. All the tested immunological paraters of experimental groups were significantly increased than the control. During the challenge experiment, the A. hydrophila load from skin and muscle tissues were also isolated and the result observed that, A. hydrophila load was significantly reduced, which depending on the concentration of probiotic strain.