||Caption: Aeromonas hydrophila - Gram-negative, facultatively anaerobic, oxidase positive, rod bacterium (prokaryote). Aeromonas hydrophila is a bacterium that occurs in all types of aquaticenvironments. It is motile by polar flagella and can survive in aerobic and anaerobic environments. A. hydrophila causes diseases (infections) especially in fresh water fish including tail rot, fin rot, red fin disease and hemorrhagic septicemia. Hemorrhagic septicemia in fresh water fish is characterized by the presence of small surface lesions, often leading to sloughing off of the scales, hemorrhaging in the gills and anus, ulcers, abscesses, exophthalmia (bulging eyes), and abdominal swelling (dropsy). It also causes infections in other aquatic animals such as amphibians. When A. hydrophila enters the body, it travels through the bloodstream to the first available organ. It produces Aerolysin Cytotoxic Enterotoxin (ACT), a toxin that can cause tissue damage. In humans Aeromonas hydrophila causes gastroenteritis. It is also associated with cellulitis, an infection that causes inflammation in the skin tissue and can cause diseases such as myonecrosis and eczema in immunocompromised patients. It is also very hard to kill, because it is a resistant bacterium to certain antibiotics and chemotherapeutic agents. Chloramphenicol, florenicol, tetracycline, sulfonamide, and nitrofuran derivatives are used to eliminate and control the bacterial infection.