Pigment Cell Neoplasms in Amazon Mollies

Approximately 5% of the Amazon mollies in a clone (M-clone) predisposed to cutaneous pigment cell neoplasms develop tumours (Schartl et al., 1997). Clones occur in this gynogenetic species because descendants from a given female usually contain only maternal DNA. Embryogenesis of diploid eggs occurs after insemination by males of related species, but paternal DNA is not usually contributed to offspring. However, in rare matings paternal microchromosomes enter the egg, resulting in a new clone. Fish of the M-clone have macro-melanophores, the cell type giving rise to melanoma in the related genus Xiphophorus, but the oncogene involved in melanoma of Xiphophorus does not appear to be involved with the pigment cell tumours of Amazon mollies.

Although M-clone Amazon mollies are genetically uniform, there is considerable variation in the pigment cell neoplasms of these fish (Schartl et al., 1997). There is variation in the growth, invasiveness and age of onset; and yellow pigment occurs in addition to the more common melanin. Schartl et al. (1997) consider these neoplasms to be chromatoblastomas.

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