Pathological Findings in Rainbow Trout (Oncorhynchus mykiss Walbaum, 1792) Experimentally Infected with Yersinia ruckeri


Abstract: The aim of this study was to evaluate the pathological findings in rainbow trout experimentally infected with Yersinia ruckeri. For this purpose, 42 [1 control group (10 fish) and 1 experimental group (32 fish)] of rainbow trout were used. Yersinia ruckeri serotype I (R0072) at a concentration of 3 x 10^6 cfu/ml (0.1 ml per fish) was intraperitoneally injected into the experimental group, whereas the control group was subjected to the same volume of sterile saline. Following the intraperitoneal injection, between 4 and 26 days, fish that died due to natural infection and those killed were necropsied and macroscopic and microscopic findings were determined. Macroscopically, in the acute form, hyperemia and hemorrhages were observed, especially at the base of the fins, around the anus and eyes, on the swim bladder and in the gills. In the chronic form, dark pigmentation or depigmentation of the skin and yellow-grayish discoloration in the liver were noted. In addition, the kidney and spleen were dark in color and smaller than those observed in the control fish. Microscopically, in the acute form, edema, hyperemia, hemorrhage and desquamation of the epithelial cells in the secondary lamellae and a significant decrease in the numbers of lymphoid cells in the kidney were seen. In the spleen, focal necrosis was the most important microscopic finding. In the chronic form, hyperplasia of the interlamellar cells of the primary lamellae, fatty changes in the liver and many large mononuclear cell proliferations with slightly incised nucleus in the hemopoietic tissue of the kidney were observed. This is the first pathological study on rainbow trout experimentally infected with Yersinia ruckeri in Turkey.

Keywords: Yersinia ruckeri, rainbow trout, pathological findings

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