nile tilapia fry with approximately 3 g in body weight and 3.5 cm in body length were purchased from khon kaen inland fisheries research and development center, khon kaen, thailand.
fish were acclimatized and fed with commercial fish food pellet in aquarium contained declilorinated tap water with continuously aeration for 10 day the 2-3 fish were randomly collected to perform bacterial isolation from the kidney to ensure there was no pxeexistent a. hydrophila