Abstract. Dermal sarcoma is a benign skin tumor of adult walleyes (Stizostedion vitreum vitreum) with a suspected viral etiology. A laboratory study was initiated to determine if the tumor could be experimentally transmitted by inoculating young walleyes with materials prepared from tumors from adult fish. Eighty walleye fingerlings were divided into four groups of 20 fish each. Two groups were inoculated intramuscularly at 4 months of age either with live tumor cells or with cell-free filtrates of sonicated tumor cells. The two other groups were used as controls and were inoculated either with cultured cells from normal walleye fry or with tissue culture media. Neoplasms, similar to the dermal sarcoma affecting adult walleyes, were observed after 4 months only in fingerlings inoculated with cell-free filtrates of sonicated tumor cells. Like the tumor affecting wild adult walleyes, the transmitted tumors were restricted to the dermis and originated from the superficial surface of scales. They-never invaded locally and never metastasized. The transmitted tumors differed from tumors of adult walleyes in their severity and the absence of osteoid. The multicentric origin of transmitted walleye dermal sarcoma suggests that the virus spreads systemically and that tumor cells are polyclonal. This successful transmission of the lesion, along with the presence of C-type virus particles budding from tumor cells in two of seven tumor-bearing fingerlings, supports a retroviral etiology.Key words: Fish; neoplasm; retrovirus; transmission.Walleye dermal sarcoma is a benign skin tumor of adult fish diagnosed in adult walleyes from a number offish populations throughout North Amefica.g-ll The tumor has been most often observed during the spring removed from some of the fish at the hatchery and stored at -90 C until used. Other tumor-bearing walleyes were transported to Cornell University, where they were maintained in temperature-controlled holding Units (Frigid Units, Inc., Prevalence of the lesion is seasonal; it is common size (75 mm). Fingerling walleyes were obtained for this study in the spring and fall, but rare in the summer.' Walleye from the NYSDEC South Otselic Fish Hatchery on 22 June dermal sarcoma is also age-related; it is not observed 1988. Upon arrival in our laboratory, the fish were placed in sexually immature fingerlings. I in temperature-controlled holding units where they were kept In order to demonstrate the viral etiology for this without treatment during an acclimation period of 6 weeks. neoplasm and to provide a model for studying the During the entire holding period, the fish were provided a seasonal prevalence of dermal sarcoma, transmission ration of swim-up fathead minnow (Pimephales P o m e h )
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