Abstract
Application of probiotics in aquaculture helps to improve the survivability, growth and immunity of aquatic organism in sustainable aquaculture practices. This study was conducted to evaluate the probiotic potentiality of Streptomyces antibioticus EW1 and Bacillus cereus EW5 isolated from the digestive tract of earthworm (Eisenia fetida) and also determine their effects as probiotic in juvenile catfish (Heteropneustes fossilis). The bio safety assay confirmed that the isolates were not pathogenic to the host fish. These strains were able to survive in acidic as well as alkaline conditions, higher tolerance to bile salt as well as gastric juice and high surface hydrophobicity to solvents and displayed extracellular enzyme activity and moreover susceptibility to various antibiotics. Their antimicrobial activity was assessed against two fish pathogens: Aeromonas veronii (MN602971) and Stenotrophomonas maltophilia (MN602972). Among two isolates, the EW1 confirmed good antimicrobial activity against fish pathogens. The isolated bacterial strains were identified and established on the basis of their colony morphology, biochemical characteristics and 16S rRNA sequencing which revealed that the isolates exhibited 99 % sequence homology with Streptomyces antibioticus EW1 (MH301104) and Bacillus cereus EW5 (MH301102). A 45-day feeding trial was conducted to examine the effect of probiotic inoculated fish diet for the freshwater catfish Heteropneustes fossilis. Among three isonitrogenous (30 % CP) diets: RD (reference diet), T1 (diet with Streptomyces antibioticus) and T2 (diet with Bacillus cereus), fish fed T1 diet showed significantly higher growth, digestibility and higher values of crude protein and lipid than fishes reared with T2 and RD. The result of present study suggest that diet supplemented with Streptomyces antibioticus (T1) can be perform as safe probiotic and alternative protein source in the formulation of diet for H. fossilis.
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