Morphologic and immunohistochemical investigations in rainbow trout (Oncorhynchus mykiss Walbaum, 1792) experimentally infected with vibrio anguillarum

In this study, experimental vibriosis caused by Vibrio anguillarum O1 (ATTC 43305) was constituted in rainbow trout using intraperitoneal route and immersion method. For this purpose, 56 rainbow trout (weight 80 ± 10 g and 10-12 cm in size) were divided into four groups [two experimental (Intraperitoneal Group (IP), n: 20 ? Immersiyon Group (IM), n: 20) and two control (Intraperitoneal control (CIP), n: 8 - Immersiyon control (CIM), n: 8)]. Vibrio anguillarum at a concentration of 5.5x108 cfu/ml (0,1 ml per fish) was injected intraperitoneally to the IP Group. The IM group were immersed into 30 l water inoculated with 50 ml of bacterial inoculum (5.5x105 cfu/ml) for thirty minutesThe first death was observed on the 3th day of application in the IP, and on the 5th day of the IM group. Dead or killed fish were necropsied, tissue samples collected, fixed in 10 % neutral-buffer formalin solution, embedded in paraffin wax, sectioned at 5 µm and stained with hematoxylin and eosin (H&E) and immunoperoxidase techniqueThe lesions were different in location depending on the inoculation routes. Irregular swimming, hyperemia in the fins and around the anus, hemorrhage in the muscle, liver and gill and enlargement in the spleen were observed macroscopically in the IP group. In microscopic examination, the muscle, liver and spleen showed hemorrhage and necrosis with no inflamatory response. In the gills, there were odema, telangiectasi, necrosis of epithelium and an increas in the number of eosinophilic granuler cells (EGC). Activation of the ventricular endothelial macrophages and epicarditis in the heart, eosinophilic hyalin droplets in the tubular epihelium of the kidney and an increas in the number of EGC in the stomach were determined. With immunoperoxidase staining, bacterial antigen was seen in the muscle, liver, spleen, gills and swim bladder. In the IM group, macroscopically, paleness and haemorrahages in the gills and discolaration in the liver were determined. The swim bladder were also opaque. At the microscopic examination, there were odema, desqumation of the epithelial cells, telangioectasie and an increas in the number of the EGC. In the liver, hemorrhage, fatty changes and necrosis were observed. Odema and hemarrhages were generally found in serosa of the swim bladder. Immnunohistochemically, positive reactions were particularly observed in the gills and to a lesser extent in the heart, liver, spleen, pyloric seceae and intestinesIn conclusion, pathological findings seen in the experimental vibriosis were comparatively examined and distrubution of the bacterium in tissues were evaluated immunohistochemically.Key Words: Immunohistochemistry, Vibrio anguillarum, pathological findings, rainbow trout