Isolation and Selection of Probiotic Bacteria from Nile Tilapia (Oreochromis niloticus) as Probiotics for Promoting Fish Growth

Bacillus spp. and lactic acid bacteria (LAB) were isolated from samples of Nile tilapia body (gastrointestinal tract, mucus, and fish scales) and fishpond water in Songkhla province, Thailand. Fifty-one bacterial isolates were obtained, and only 44 Gram-positive isolates were tested for their probiotic properties. These isolates were selected based on the ability to inhibit serious pathogens in tilapia, namely Streptococcus agalactiae and Aeromonas hydrophila; only isolated bacteria that can inhibit both fish pathogens were selected. Hence, 6 selected bacteria were further tested for their nutrient digestion, adhesion, and tolerance to acids and bile salts. It was found that only5 isolates passed those tests. There were three isolates of bacilli and two isolates of LAB. The five isolates were identified using the 16s rRNA gene method and API test kits, and only two isolates (Bacillus subtilis HW3B and Lactiplantibacillus plantarum DW5L) that could be safe for fish and humans were selected for further studies as probiotics for fish cultivation.