Last updated: 07/14/24
The XFins site includes images and information that I hope will be useful to both beginners and advanced hobbyists. My primary focus as a hobbyist is the development of colorful fancy finned swordtails including hifin and lyretail varieties. Many of the beautiful fancy finned fish that are available today are the product of interspecies hybridization. All species of Xiphophorus are potential sources of genes or gene modifiers that when expressed in a different species, can produce novel color patterns or fancy finnage. I have used natural matings and artificial insemination to search for new hifin, lyretail, and

Roy Levine, Ph.D.


color gene modifiers in several wild species and the results are shown here.

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Takeshita hifin article
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Developing a Line of High Quality Hifin Maculatus

All of the F1 hifin males have wide dorsal fins indicating that the wide dorsal is a dominant trait in males. Body size and hifin length are variable and should be improved by selective breeding. It is striking that the dorsal fins of the F1 hifin females are so underdeveloped compared to their male siblings. This sex-linked difference in hifin development also occurs in swordtails and variatus platies. Female hifin swordtails containing long, flowing dorsal fins are not commonly available, but they do exist. Interestingly, the male hifin siblings of these females do not generally have long flowing dorsals. The modifier genes that control hifin development in males and females are distinct.
Female hifin swordtail with a long, flowing dorsal fin
Difficulty Developing Lines of High Quality Lyretail Maculatus
Wildtype male maculatus and variatus platies do not have sword-like extensions from their caudal fins. Transfer of the dominant lyretail gene from a swordtail to a maculatus platy generally results in poor quality lyretail maculatus containing short, nonsymetrical lyretails.
The platies shown above express the dominant lyretail gene, but they only exhibit a partial lyretail phenotype. Typical lyretail characteristics that are commonly present include the extended second ray of the dorsal fin, larger pectoral fins, and an extended gonopodium as seen on the two males. In most lyretail platies the lyretail is underdeveloped; either short and nonsymmetric or not present at all. A gene that suppresses caudal extensions in maculatus and variatus is likely preventing the growth of a long, symmetrical lyretail.
These lyretail maculatus have relatively well developed, symmetrical lyretails. However, this lyretail phenotype does not always breed true. Several rounds of selectively breeding good lyretail females and sibling non-lyretail males will be required to establish a high quality lyretail maculatus line.
This single "bumblebee" lyretail swordtail was present in my stocks. Transferring the "bumblebee" trait from a maculatus platy to a swordtail frequently produces a melanoma, but this fish is cancer-free. Whether the black coloration is heritable in this case or has resulted from a non-heritable somatic mutation is unknown.
Lyretail Swordtails
The lyretail of this attractive orange lyretail swordtail is devoid of orange pigment resulting in clear extensions.
In general, the lyretail trait seems to suppress the full expression of a coexpressed hifin. The dorsal fin of this black lyretail hifin swordtail is not suppressed by the lyretail trait and is extremely long.
Variatus-Swordtail Hybrids
These variatus-swordtail hybrid hifin males have large, well proportioned dorsal fins. First generation hybrids typically have large bodies, but lack the intense red caudal fins found on some wildtype variatus males.
As with most Xiphophorus-derived hifin females, the dorsal fins of these hybrids are small, and not well developed compared to the male.
These male variatus lyretail hifin hybrids have red caudal fins and the Parr markings (short black vertical stripes) found on the body of some wildtype variatus. The gonopodiums of these fish are not fully developed and whether these fish will be fertile is uncertain.