Outbreak of a novel disease associated with Citrobacter freundii infection in freshwater cultured stingray, Potamotrygon motoro

An outbreak of a novel disease characterized by serious hemorrhage in the abdomen, ascites and bleaching of the liver was recorded in the freshwater cultured stingray Potamotrygon motoro, which is a cartilaginous fish related to sharks, in Panyu, Guangdong province of South China. The bacterial isolates from the lesions of diseased P. motoro exhibited the same phenotypic traits and biochemical characteristics and were identified for the first time as Citrobacter freundii according to biochemical characteristics and molecular identification with the 16S rRNA gene. In challenge trials, P. motoro injected intraperitoneal with the C. freundii P2 developed similar pathological signs to the naturally diseased fish. Furthermore, histopathology of diseased fish infected with C. freundii showed moderate lipid degeneration in the liver, macrophage aggregations of the lymphoid tissue in the spleen, and microglia aggregation in the brain.