Shewanella algae is a gram-negative, rod-shaped, motile bacillus with a single polar flagellum. S. algae is found in warm marine environments throughout the world, and is isolated from seawater.1 The tiger shovelnose catfish (Pseudoplatystoma tigrinum) is the member of the genus Pseudoplatystoma and the family Pimelodidae which belongs to the class Actinopterygii. Pseudoplatystoma species are all large, boldly striped or spotted catfishes, they are familiar due to their distinctively marked color patterns.2 Here we described the histopathologic lesions of fibrinous peritonitis caused by S. algae in tiger shovelnose catfish.
A male, tiger shovelnose catfish raised in Hanwha Aqua Planet Jeju was submitted to the Pathology Department of Veterinary Medicine, Jeju National University. Necropsy was performed and visceral organs were fixed with 10% neutral buffered formalin and prepared into paraffin sections and stained with hematoxylin & eosin for light microscopy. Fibrinous materials of visceral surface were aseptically collected for bacterial culture, and were inoculated on sheep blood agar and anaerobically incubated for 48 h at 37°C. Isolated bacteria were confirmed using VITEK 2 system.
Grossly, the catfish had severe damage on the fin and tail. A turbid, sticky, dark-red fluid was found in the abdominal cavity. Histopathologically, diffuse fibrinous peritonitis in the serosa of the spleen and kidney was observed. Diffuse, fibrinous epicarditis was presented in the heart. Large amount of the intra-lesional bacterial colonies were adhere on the serosa of the spleen, kidney, and pericardium of the heart. In bacterial examination, gram-negative rod shaped bacterial colonies were successfully isolated from blood agar plate. The isolated bacteria were mucoid colonies with β hemolysis on blood agar. These bacteria were confirmed as S. algae by the VITEK 2 system.
The etiology of S. algae infections to freshwater fish (tiger shovelnose catfish) is unknown.2 According to literature, S. algae could cause an infection to both marine animals3 and freshwater fish. Based on the gross findings and histopathology, this tiger shovelnose catfish was diagnosed with fibrinous serositis caused by S. algae infection.
* Presenting author
1. Holt HM, Gahrn-Hansen B, Bruun B. Shewanella algae and Shewanella putrefaciens: clinical and microbiological characteristics. Clin Microbiol Infect. 2005;11:347–352.
2. Buitrago-Suárez UA, Burr BM. Taxonomy of the catfish genus Pseudoplatystoma Bleeker (Siluriformes: Pimelodidae) with recognition of eight species. Zootaxa. 2007;1512:1–38.
3. Mulvany E, Lawler DF, Evans RH. Peritonitis secondary to multiple, full-thickness jejunal wall perforations in a California Sea Lion. PMMC Case Rep Mar Mamm Pathol. 2010;1:1–9.