Bacterial fish pathogens are pervasive in aquaculture. Control of bacterial fish pathogen is a difficult task among aquaculture practitioners. A large number of antibiotics are used for the control of prevalent bacterial pathogens in aquaculture. This may lead to drug resistance among pathogens and further treatment will be ineffective. Here, we can use probiotic bacteria as a biocontrol agent in fish disease and it is a novel field. In this study, antimicrobial potential of the bacterium Bacillus coagulans (MTCC-9872) has been evaluated through in vitro antagonistic activity of cellular preparations/components against potent pathogens. The cellular preparations/components such as Ethyl acetate extract, whole-cell product, heat-killed whole-cell product, and filtered broth were exhibited bactericidal activity against the tested pathogens. Bactericidal activity varied among different cellular preparation/components. The tested bacterium effectively produced biofilm as significant as tested positive control in a microtitre plate and effectively adhered on to the glass slide. In addition, the bacterium was capable of producing extracellular enzymes necessary for the digestion of food materials and was capable to grow in fish mucus from Oreochromis niloticus. The bacterium tolerated bile juice secreted by the host. Moreover, intraperitoneal injection of the bacterium did not induce any pathological signs, symptoms or mortalities in Oreochromis niloticus and revealed the safety of this bacterium in the fish.