Prawn samples: For histopathological and bacteriological analysis, diseased freshwater prawn, (Macrobrachium rosenbergii) measuring 6 to 8 cm in length were collected from commercial hatchery in Behera Governorate, Egypt, in June 2006 and July 2007. The collected samples were transferred alive to the laboratory then placed in glass jars containing water from the natural habitat. Jars were maintained at temperature of 26-28 °C and aeration was supplied by compressed air with diffusers.