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iphophorus is a freshwater fish genus comprised of 23 species. These fishes live in eastern drainages in Mexico, Guatemala, Belize and Honduras, with most of the described species living in Mexico. The taxa make up 3 groups, the Northern Swordtails, the Southern Swordtails and the Platyfish. If these names are familiar to you, there is a good chance that you have seen these fish at pet stores, as they are very popular with hobbyists.

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t was realized as early as the 1920's that one could make hybrids between the different species. These hybrids were normally viable and could produce subsequent generations of offspring. In some cases, one simply had to place one Xiphophorus species next to another in an aquarium, and they would reproduce. In many situations, the resulting hybrid fish that were produced would show traits from both parent species, and were intermediate in appearance. For example, several dominant pigment patterns derived from two fish strains would appear within F₁ hybrids giving them characteristics of both species. In other cases, the hybrid fish were quite different from either parent, such as when fish developed beautiful red or yellow colors. In such situations, pigment patterns were derived from one of the species and became enhanced in the hybrid offspring. It was also realized by scientists in Germany and the United States, that hybrid fish sometimes also developed melanoma, one of deadliest skin cancers. These melanomas were derived from improperly regulated melanistic pigment patterns. Scientists immediately began to study Xiphophorus hybrids, since they realized that they had discovered an animal model that could be useful in the study of cancer.

Genetic cross between two Xiphophorus species that leads to the development of melanomas:

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oday, we continue the work that was begun by the scientists in the 1920's and pursued by other researchers for the last 70 years. Our work focuses on studying melanoma and other cancers that form in hybrid fish.

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