Probiotics play vital roles in improving growth, survival, and immune responses and inhibit the growth of pathogenic bacteria in freshwater fish. This study was conducted to isolate potential probiotics from Channa punctatus and Channa striatus and to evaluate their effect on Labeo rohita fingerlings. Among the isolates, Bacillus paramycoides PBG9D and BCS10 (1) exhibited antimicrobial activity against the fish pathogen Aeromonas hydrophila. Both strains showed tolerance to acidic and alkaline pH (2, 3, 4, 7, and 9) and bile salts (0.3%) and exhibited strong adhesion capacity. After in-vitro assessment, these strains were evaluated on the growth performances of rohu fingerlings challenged by Aeromonas hydrophila for 4 weeks. The study consisted of six groups, each containing 6 fish. Group (I) was the control, fed a basal diet; group (II) contained a pathogen and was also fed a basal diet; group (III & IV) was given a probiotic supplemented experimental diet; Fourth group (V & VI) contained a pathogen and was given a probiotic supplemented experimental diet. After the 12th day of experiment, rohu fingerlings of pathogen (II) and probiotic + pathogen (V & VI) groups were intraperitoneally injected with 0.1 mL of Aeromonas hydrophila. After 4 weeks, no significant differences in weight gain, weight gain %, and feed conversion ratio were observed in probiotic (III & IV)- fed groups compared to control. However, the specific growth rate was significantly improved in probiotic fed groups compared to other groups. Survival rate and condition factor were significantly similar in all groups. After injection, abnormal swimming, loss of appetite and weight loss were observed in the pathogen (II) group, while no such symptoms were found in the probiotic + pathogen (V & VI)- groups, confirming the effects of probiotics. The overall results of the study revealed that dietary supplementation with Bacillus paramycoides strains could improve the specific growth rate and disease resistance against Aeromonas hydrophila in Labeo rohita.
Keywords: Aeromonas hydrophila; Bacillus paramycoides; Labeo rohita; antimicrobial activity.