RESUMEN
Dynamics of development and morphology of hyperplastic skin lesions ("hoods") on the head of goldfish, which were bred using artificial selection for more than thousand years, were studied. During monitoring of hundred fishes, at the age of 6 months "hoods" were found in 39.5%, among 14 months-old fishes in 60,7%. Morphologic examination of "hoods" on various stages of development revealed epithelial hyperplasia with increased clear mucous cells number, dermis thickening and oedema. On later stages developed papillomatous outgrowth and areas of epithelial intrusion. The comparative oncology analysis allow to hypothesize these skin growth to be a genetically determined benign neoplasm. This is the first example of artificially selected neoplasm described in the literature. It supports our hypothesis of the possible evolutionary role of tumors.