First report of Citrobacter freundii infection in Exotic Tropheus spp.

Abstract

The ornamental fish industry has spread globally and it involves many different species of freshwater and marine fish. It is important to detect infectious diseases in aquarium fish due to their economic value and for the welfare of these animals. A case in which there was mass mortality of valuable exotic aquarium fish, Tropheus spp. was determined in July 2021, and the causative agent of infection was studied. The clinical and pathological symptoms of the disease were determined and the mortality rate recorded. After bacteriological examination, pure colonies were found to be present in tryptic soy agar (TSA) from bacterial isolations of the kidney, liver and spleen of the diseased fish. Gram stain, motility, oxidase and catalase activity of the isolated bacteria were determined and API 20E tests were used to provide the biochemical profile of the strain. Both juvenile and adult Tropheus spp. individuals were affected and 100% mortality was observed. Erratic swimming, inappetence, darkened skin, exophthalmus, abdominal distention, petechial hemorrhages on the skin, and hemorrhages on the fin bases and around the anus and mouth were found. Enteritis, gronulomas in the kidney, spleen, and pale liver were observed at necropsy. Gram-negative motile rods were identified as Citrobacter freundii by biochemical and 16s rRNA sequence analyses. To our knowledge, this is the first report of C. freundii infection in Tropheus spp., which is one of the valuable aquarium cichlid species.