Let’s Get Together: Fish Hybrids and Melanoma


Bob Marley

While playing soccer in Paris in 1977, legendary reggae composer Bob Marley injured his big toenail, opening up an old wound. Despite removing the nail, his toe got worse. The doctors diagnosed the irregularly shaped, non-healing bruise as melanoma, a type of skin cancer.

The diagnosis of skin cancer is not uncommon; one in every five people will develop skin cancer in the course of their lifetime (“Melanoma,” 2013).

For the vast majority, the diagnosis is treatable and highly survivable. But in Marley’s case, the news was devastating; melanoma is the aggressive cancer responsible for the vast majority of skin cancer deaths, killing one person every hour (“Melanoma,” 2013).

In early stages, like Bob Marley’s case, melanoma is treatable. Amputation is just one of many treatment options, depending on size, location, and severity of the cancer. However, because of his religious beliefs, Bob Marley refused to amputate his toe, leading to his premature death at just 36, after the melanoma spread to his vital organs.

Value of Models

Animal models such as the swordtail-platyfish hybrid are used to better understand how melanoma appears and spreads.

Although there are other fish models used in melanoma research, swordtail-platyfish hybrid models are unique due to their ability to spontaneously develop melanoma.

These hybrids are a second generation cross. First, a pigmented platyfish, Xiphophorus maculates, and a nonpigmented swordtail, Xiphophorus hellerii, are crossed; then, the resulting hybrid is crossed with another swordtail to form a Xiphophorus hybrid that is ¾ swordtail and ¼ platyfish.

These crosses are necessary to combine growth modifying factors from the swordtail with a dominant allele controlling the distribution of melanocytes from the platyfish. In wild platyfish, these melanocytes do not produce pigmentation, meaning these fish cannot get melanoma. However, in the presence of the swordtail’s growth factors, these melanocytes will produce melanin, which leads to melanoma. In essence, the best genes (or worst, depending on how you think about it) are taken from each species and combined in these hybrids, making them extremely prone to melanoma. Additionally, the type, progression, and metastasis patterns of the melanoma in fish are often similar to humans (Meenhard, 2013).

[Photo: Xiphophorus maculatus offspring by Ude, License: GNU Free Documentation License; Photo: Type of fish that was flown on STS-90 by NASA, License: Public Domain]

[Photo: Xiphophorus maculatus offspring by Ude, License: GNU Free Documentation License; Photo: Type of fish that was flown on STS-90 by NASA, License: Public Domain]

Using swordtail-platyfish hybrids, scientists found a proto-oncogene – a normal gene that causes cancer when turned on – that causes spontaneous melanoma formation in these fish. This gene, XMRK, or Xiphophorus Melanoma Receptor Kinase, resides on the sex chromosome and allows melanoma to be inherited.

The importance of studying XMRK in swordtail-platyfish models is the universal commonalities among proto-oncogenes in different organisms, meaning a similar gene with similar inheritance patterns could very well be what causes melanoma in humans.

The End of an Era?

Even with all the advances made using swordtail-platyfish models, these animals are already being phased out for Zebrafish models, which have many practical advantages such as external fertilization, which allows for analysis of embryo development. In addition, medakas, or Japanese rice fish, are starting to gain prominence as an alternative melanoma model because they can also express the XMRK gene.

In the future, a multi-pronged approach using a combination of new drugs to target each specific melanoma-inducing protein would be productive in halting the disease. Dr. Keith Flaherty of the Dana-Farber/Harvard Cancer Center is just one of many optimistic oncologists who believe this new method, which has worked against H.I.V., would be just as effective against melanoma. “‘We just need,’ Dr. Flaherty said, ‘to find the right combination’” (Harmon, 2010).

This method of treatment could call for multiple models, some that have not even been identified yet. This impetus will invariably lead to the discovery of more complete and diverse animal models. For now, the swordtail-platyfish hybrids are a great step beyond conventional models and are music to the ears of melanoma patients, much like Bob Marley’s music which transcended race and time to serve as inspiration to millions.

In Brief:

  • Melanoma is a deadly skin cancer that originates in melanocytes, cells that produce pigment in skin and other tissue.
  • The swordtail-platyfish hybrid combines the traits of the swordfish and the platyfish to produce a model that is highly prone to melanoma.
  • Through the swordtail-platyfish model scientists have discovered a gene that, when turned on, causes melanoma.
  • New combinations of treatments and gene therapies might be developed as a result of the information provided by the swordtail-platyfish hybrid model.

Works Cited

This article was written by cYw24. As always, before leaving a response to this article please view our Rules of Conduct. Thanks! -cYw Editorial Staff


Author: cYw24

Hi everyone! After spending some time as part of the Creative Transfer Team, I'm super excited to be working on the other aspect of the articles-- namely, writing. While writing and researching melanoma and fish hybrids, one of the challenges I faced was finding enough information about swordtail-platyfish hybrids, especially since zebrafish models are much more commonly used. But that's all part of the research process, which I am immensely grateful to have the opportunity to go through and share with readers. Outside of biomedical research, some of my interests include math, chemistry, quiz bowl, cross country, and tutoring.

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    Very nicely written summary of this work.

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      Thanks for reading! I tried to make the more ‘scientific’ aspects of the article accessible; I’m glad that it turned out well!

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    Interesting article! I have been working with zebrafish in the pharmaceutical industry for 7 years and it has been fascinating. However, I think there are many more fish models that have yet to be explored such as the platy and swordtail. For example, there are several species of fish that have caught my attention: the glass catfish (Krypototerus bicirrhis) could be used as a model for all kinds of cancers since this fish is “see-through” its entire life and large enough that you don’t need a microscope. Goldfish have been used, too, for a number of disease models and may be under utilized in research. There is a huge area of untapped opportunities to find animal models that are less expensive than rodents, have advantages over rodents and can deliver information much more quickly!

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      Thank you! While researching, I came across many fish models including zebrafish, which are popular because of their clear embryos, among other reasons. Each of the fish species you mentioned has advantages to a specific disease, or they could be crossed to form hybrids, as with the case with swordtail-platyfish hybrids.

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