A COMPARISON OF PATHOLOGICAL-CHANGES CAUSED BY VIBRIO-ANGUILLARUM ANDITS EXTRACELLULAR PRODUCTS IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

Some hematological parameters and histopathological changes in the liv er, spleen, kidney, gills, gut, skin, muscle and heart of rainbow trou t (Oncorhynchus mykiss) injected intraperitoneally with virulent Vibri o anguillarum or with V. anguillarum extracellular products (ECPs) wer e compared. The number of circulating red blood cells, the hematocrit and hemoglobin values decreased in the fish injected with either bacte ria or ECPs compared with controls. The erythrocyte sedimentation rate increased in both groups of injected fish; however, the serum protein levels were similar to those observed in control fish. Light and elec tron microscopic observations of samples obtained from fish injected w ith V. anguillarum cells or its ECPs revealed similar histopathologica l changes in most tissues. Both groups of fish showed degeneration and necrosis of hepatocytes, vasodilation of the glomerular capillaries, cloudy swelling and hyaline droplet degeneration of the epithelial tub ular cells, edematous gills, desquamation of the intestinal mucosa and necrosis of the muscle fibers at the site of injection. However, the bacterium multiplied extensively in the kidney and spleen where it cau sed more acute alterations than ECPs. Based on these results, it was c oncluded that the extracellular products play an important role in the virulence mechanisms of V. anguillarum.