Neurogenic tumors in coho salmon (Oncorhynchus kisutch) reared in well water in Japan.

Neurogenic tumors were found protruding from various parts of the body of 23 coho salmon. The tumor-bearing fish were first- or second-generation fish derived from eggs imported at the eyed stage to Japan from the United States. Twenty-two of the tumors were in young adults and varied from 14 to 80 mm in maximum diameter. Histologically, the tumors were composed of spindle-shaped cells with abundant fibrous stroma. One tumor showed typical nuclear palisading. All tumors in young adults invaded locally muscle and adipose tissues. These tumors were similar in histologic appearance to malignant schwannomas in humans. One tumor found in a fingerling coho salmon was identified as an ependymoblastoma. The Vectstain avidin-biotin-peroxidase complex immunoperoxidase staining procedure for S-100 protein revealed that the S-100 protein existed in an ependymoblastoma and in areas of typical nuclear palisading in a malignant schwannoma in coho salmon. The occurrence of soft tissue tumors in coho salmon was first recorded in Japan. The morphology and etiology of the present cases were compared with those of the tumors in salmon reported from the United States. Judging from the conditions in which the fish were reared, the development of these tumors was not related to halogenated compounds formed during water chlorination, as suggested previously. The environmental factor(s) responsible for their development has not yet been identified, and genetic influences may have been a contributory factor.