Characterization of Lesions in Diseased Fishes; Isolation and Identification of Edwardsiella Tarda from Selected Lakes and Ponds Of Central Ethiopia

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Addis Ababa University


Fish is a nutritious animal rich in protein and consumed by many peoples throughout the world. A cross-sectional study with purposive sampling was conducted from December 2020 to May 2021 with the objectives of lesion characterization in diseased fishes, isolation, and identification of Edwardsiella tarda. From Batu, Langano, and Babogaya lakes and ponds in Bishoftu, a total of sixty fishes were examined for gross lesions. Skin, muscle, gill, liver, kidney, spleen, and heart were collected for microscopic lesion characterization and Edwardsiella tarda isolation. Grossly, few lesions were observed. Out of 60 samples, 25% (n=15) were positive for Edwardsiella tarda by conventional PCR. A statistically significant difference (P<0.05) was observed in the frequency of identifying E.tarda between the three study areas and four fish species. After the histopathological process and staining, tissues were divided into two based on E. tarda confirmation. Gills from Edwardsiella tarda positive fishes revealed hyperplasia, focal necrosis, and swelling of the lamellar epithelium. Microscopic lesions in the liver include nuclear condensation, cytoplasmic vacuolation, and swelling of hepatocytes. Lesions in the hepatic blood vessels comprise severe hyperplasia of the endothelium, hyperemia, and elastic fibers in the intima of hepatic artery. Kidneys of Edwardsiella tarda positive fishes had suppurative interstitial nephritis, melano-macrophage deposition in interstitium, and interstitial hemosiderin deposition. Examination showed infiltration of inflammatory cells and focal area necrosis of the epidermis, lymphocyte infiltration in muscle, and accumulation of hemosiderin pigments in spleen. Microscopic lesions in Edwardsiella tarda negative fishes indicated significant changes like lamellar epithelial degeneration with vacuolation, and total necrosis of structure in gill, periportal hepatitis, and hepato-necrosis with vacuolation of liver, glomerulitis, multifocal tubulointerstitial nephritis, epithelial cells degeneration and cloudy swelling in kidney, dermal edema in skin and myocarditis with fibrosis of heart. Based on the study several lesions were identified from diseased fishes. Thus, further studies on lesion characterization in diseased fishes of different species with large sample sizes and study area should be conducted.



Edwardsiella tarda, Fish diseases, Lesion, Lakes