Detection of Aeromonas hydrophila from fingerling stage of Rutilus rutilus in rearing earthen ponds in north of Iran

Objective: Aeromonas hydrophila bacterium is found in all freshwater environments and in brackish water. It is a Gram negative rod that has polar flagella and is a facultative anaerobe. The etiologic agent is transmitted horizontally but not vertically. Aeromonas hydrophila causes disease in fish known as Hemorrhagic Septicemia, Motile Aeromonas Septicemia, Ulcer Disease, or Red- Sore Disease. The many synonyms of this disease relate to the lesions caused by this bacterium which includes lesions of septicemia when the bacteria or bacterial toxins are present within numerous organs within the fish, and skin ulcers. Method & Materials: In winter (2008), 200 Rutilus rutilus fingerlings (A.b.w. =5-7 gr) were collected from an earthern pond in north of Iran. The prevalence of skin ulcer in this species from mentioned area was 40%. Chemical test; some culture media (blood agar& Mac) and histopathological examination were utilized for diagnosis. Gram staining and KOH test (for differentiation of Gram diagnosis test) also were used. S.C. culture medium using for fungus detection was used too. Results & Conclusion: After sampling of moribund fish which had skin ulcer, bacteria isolated and identified biochemically to provide a definitive diagnosis. Gram staining and bacterial culture carried out. Based on these tests Aeromonas hydrophila like bacteria in this species was detected. Occurrence of superficial ulcers in mild cases and deep ulcers in acute cases were observed. Acute ulcers penetrate the muscle and in some cases scoliosis was observed due to muscle involvement. In our cases outbreak of disease are usually associated with a change in environmental conditions. Stressors, rearing condition, a sudden change of temperature, transfer of fish, low dissolved oxygen, poor nutritional status, contribute to physiological changes and heighten susceptibility to infection.

کلیدواژه ها:

Rutilus rutilus ، Aeromonas hydrophila ، skin ulcer