Screening of bacterial flora isolated from the gastrointestinal tract of silver carp broodstocks (Hypophthalmichthys molitrix) as probiotics

This study was conducted to screen 7 species of the broodstocks silver carp (Hypophthalmichthys molitrix) digestive tracts bacterial flora including Bacillus subtilis, Enterobacteriaceae, Corynebacterium jijicum, Staphylococcus, Pseudomonas, Micrococcus luteus, Aeromonas, and Unidentified. Antibacterial activities of these candidates bacterial flora were conducted under disc diffusion, well diffusion, and cross streak methods. The tree probiotics candidates (Bacillus, Corynebacterium, and Micrococcus) were shown antibacterial activity against pathogenic bacteria. Candidate Bacillus showed a significant inhibition zone (20 ml) against the pathogen in the disk diffusion method. On the other hand, the addition of 10 ml of Bacillus supernatant to Aeromonas pathogenic species leads to killing them completely at 12 hours. The pH 8 and temperature 30 o was found optimum to grow candidates bacteria and produce antibacterial bio-components. There are significant differences between 8 treatments under different dosages of candidates bacteria and control (without bacteria of beaker included silver carp larva) in fish survival (P<0.05). From this, we can conclude that the candidate Bacillus subtilis maybe can be probiotics for silver carp culture.