See text Xiphophorus is a genus of euryhaline and freshwater fishes in the family Poeciliidae of order Cyprinodontiformes, native to Mexico and northern Central America.

The name Xiphophorus derives from the Greek words ξίφος (dagger) and φόρος (bearer), referring to the gonopodium on the males.

All are relatively small fishes, which reach a maximum length of 3.5–16 cm (1.4–6.3 in) depending on the exact species involved.

In addition to those, Mexican authorities recognize the yellow swordtail (X. clemenciae) and Catemaco platyfish (Xiphophorus milleri) as threatened.

[10] The Xiphophorus Genetic stock center, founded by Myron Gordon in 1939, is an important source of these fish for research.

In particular, studies in Xiphophorus provided some early evidence that recombination controlled patterns of ancestry in hybrid genomes.

[17] For example, in the well-studied Gordon-Kosswig cross between X. maculatus and X. hellerii, hybrids develop spontaneous melanoma due to an interaction between the oncogene xmrk and a repressor locus on a distinct chromosome.

More recently, researchers have identified specific genes and even mutations causing pigment pattern variation (for instance, a spot allowing males to mimic females[20]) and investigated selective mechanisms on these traits.