Fish diseases constitute one of the most important problems and challenges confronting fish culturists. Diseases don't occur as a single caused event but are the end result of interactions of the pathogens, fish, and the environment. It has been estimated that 10% of fish loss in aquaculture is due to disease and more than 50% of these losses are due to bacterial agents. Not all V. parahaemolyticus strains have the same pathogenic potential. Vibrios are among the most common surface organisms in surface waters of the world. They occur in both marine and fresh water habitats and in associations with aquatic animals. Some species are pathogens of fish, eels and frogs as well as other vertebrates and invertebrates.