Abstract
The present authors histopathologically examined renal tumors of two 3-year old rainbow trouts, which were reared in Samegai trout culture station in 1974. The tumors were as large as the size of a hen's egg in the posterior part of the kidney. The tumor consisted of a large number of neoplastic nodules and around which neoplastic islets were scattered in the hematopoietic tissue. The histopathological examination revealed that they were nephroblastoma (known as Wilms' tumor) with two different characteristics.
Type I; Neoplastic nodules were composed of a large number of smooth muscle cells in differentiations, well-differentiated renal tubular epithelial cells and a small number of undifferentiated messenchymal cells with argyrophiric fine fibers. Mitotic figures were frequently observed in smooth muscle fibers and messenchymal cells.
Type II; Neoplastic nodules were composed of a large number of undifferentiated messenchymal cells and islets of immature renal tubular epithelial cells. Mitotic figures were numerous in both types of cells.
Metastatic lesions were not observed in both cases.
