Edwardsiellosis in red tiger skin oscar (Astronotus ocellatus)

Objective: To determine cause of death in red tiger skin oscar (Astronotus ocellatus) with clinical signs of circling around the head and toward one side and unilateral exophthalmia and to investigate histopathologic injuries in the fish. Method & Materials: In October 2008, following heavy loss in oscar fish, 2 fish with clinical signs of circling around the head and toward one side and unilateral exophthalmia were referred to bacteriology lab of Artemia Institute of Urmia University. The fish autopsized aseptically and bacterial culture in culture media of BHA, TSA and MacConkey’s Agar from internal organs were performed aerobically and anaerobically in 28°C. Bacteriological tests using routine tests such as gram staining and differential tests identified type of bacteria growth on culture media. Pathologic samples from internal organs fixated in formalin 10% were sent for histopathologic evaluations. Results & Conclusion: Gram staining and differential biochemical tests showed the isolated bacteria were Edwardsiella tarda. In autopsy, a fibrin mass attached to liver and an abscess on the liver were seen. Histologic evaluation showed severe kidney haemorrhage and swelling of tubules and presence of haemosidrine bearing melanomacrophages in kidney. In the eye severe haemorrhage was evident in sclera and subretinal space. In gills secondary filaments were defected. Between the filaments violet particles (bacterial colony) were aggregated. In brain tissue, meningo encephalitis was seen. Haemosidrine bearing melanomacrophages and neutrophils were seen all over the spleen. A large part of liver had undergone necrosis and in vicinity of liver there were a fibrotic mass and an abscess attached to the liver. Microbial culture and histopathological evaluations indicated a bacterial septicemia in red tiger skin oscar.