Banner: Depicts macromelanophore clumps at 10x magnification.
This article was originally written for “Livebearers”, the journal of the American Livebearers Association, issue #227, Summer 2015.
Most freshwater fish species available in the hobby have “green” color, livebearers being no exception. In livebearers, cells called (micro)melanophores (black) and xanthophores (yellow) create the coloration. These pigment cells are located below the (xantho-)erythrophores, other melanophores, and iridocytes (in guppies, there may be leucophores, but we won’t discuss that here). On a side note, the organization of these different pigment cells is consistent between rather distantly related species of fish. I recognise an identical order of the different layers of color cells between bettas and livebearers, despite having spit from each other roughly 90 million years ago.
By removing the black cells, the pale-yellow undercoating in revealed. This mutation is known as leucism to science, and is surprisingly common, occurring in guppies, platys, swordtails, Heterandria formosa, and I recall in mollies as well (“gold” mollies are something else entirely). This mutation is consistently recessive across different livebearing species, which makes sense from an evolutionary point of view: drab coloration would be desirable in murky water, while golden-yellow color would be obvious to predators.
“Albino” mutations, which are also common mutations, accomplish the same goal by restricting melanin production, even in the eye. This causes the “red eye” well known on albino. Albinism is not always complete (think “chocolate” swordtails), but is differentiated from Leucism by the method black pigment is removed by.
Xanthophore coloration can also be removed, and the resulting fish is theoretically colorless. In reality, the fish is a very light pink hue due to red blood vessels. However, this does make it very interesting to the breeder because the fish is nearly completely transparent!
Most freshwater fish species available in the hobby have “green” color, livebearers being no exception. In livebearers, cells called (micro)melanophores (black) and xanthophores (yellow) create the coloration. These pigment cells are located below the (xantho-)erythrophores, other melanophores, and iridocytes (in guppies, there may be leucophores, but we won’t discuss that here). On a side note, the organization of these different pigment cells is consistent between rather distantly related species of fish. I recognise an identical order of the different layers of color cells between bettas and livebearers, despite having spit from each other roughly 90 million years ago.
By removing the black cells, the pale-yellow undercoating in revealed. This mutation is known as leucism to science, and is surprisingly common, occurring in guppies, platys, swordtails, Heterandria formosa, and I recall in mollies as well (“gold” mollies are something else entirely). This mutation is consistently recessive across different livebearing species, which makes sense from an evolutionary point of view: drab coloration would be desirable in murky water, while golden-yellow color would be obvious to predators.
“Albino” mutations, which are also common mutations, accomplish the same goal by restricting melanin production, even in the eye. This causes the “red eye” well known on albino. Albinism is not always complete (think “chocolate” swordtails), but is differentiated from Leucism by the method black pigment is removed by.
Xanthophore coloration can also be removed, and the resulting fish is theoretically colorless. In reality, the fish is a very light pink hue due to red blood vessels. However, this does make it very interesting to the breeder because the fish is nearly completely transparent!
In Xiphophorus, removing xanthophores but not micromelanophores result in the “gray” phenotype. Kallman writes “The gray phenotype has a discrete pattern and can be distinguished from its wild-type siblings even with the unaided eye. It is of a dull milky-gray appearance in contrast to the olivaceous wild-type appearance.”
The Genes discussed here are all on independent loci, but it is unknown, for example, whether the locus for Gold In Xiphophorus and the locus for Gold in guppies are homologous or not.
This column will try to cover everything. I will relay personal experiences, regurgitate scientific literature, and encourage fellow hobbyists to develop impressive fancy fish. It will be about genetics, projects, ideas, standards and history. I would like to compose a series of columns on platy genetics, which will attempt to simplify down 2 years of research into the subject into a few pages. I’m sure there will be a few columns that give ideas for new breeding projects, and once we have standards, how best to go about breeding towards them. Every once in a while, an article will be about the history of fancy Xiphophorus too. I hope you enjoy this column, and enjoy your fish!
Sources:
Copeia, 1983(1), pp. 170-181. Genetic Basis of Three Mutant Color Varieties of Xiphophorus maculatus: The Gray,. Gold and Ghost Platyfish. KLAUS D.
Shaddock, Philip. "The See-thru guppy: a transparent fish model." AACL Bioflux 2.2 (2009): 137-145.
Near, Thomas J et al. "Phylogeny and tempo of diversification in the superradiation of spiny-rayed fishes." Proceedings of the National Academy of Sciences 110.31 (2013): 12738-12743.
Vrijenhoek, RC. "An allele affecting display coloration in the fish, Poeciliopsis viriosa." The Journal of heredity 67.5 (1975): 324-325.
This column will try to cover everything. I will relay personal experiences, regurgitate scientific literature, and encourage fellow hobbyists to develop impressive fancy fish. It will be about genetics, projects, ideas, standards and history. I would like to compose a series of columns on platy genetics, which will attempt to simplify down 2 years of research into the subject into a few pages. I’m sure there will be a few columns that give ideas for new breeding projects, and once we have standards, how best to go about breeding towards them. Every once in a while, an article will be about the history of fancy Xiphophorus too. I hope you enjoy this column, and enjoy your fish!
Sources:
Copeia, 1983(1), pp. 170-181. Genetic Basis of Three Mutant Color Varieties of Xiphophorus maculatus: The Gray,. Gold and Ghost Platyfish. KLAUS D.
Shaddock, Philip. "The See-thru guppy: a transparent fish model." AACL Bioflux 2.2 (2009): 137-145.
Near, Thomas J et al. "Phylogeny and tempo of diversification in the superradiation of spiny-rayed fishes." Proceedings of the National Academy of Sciences 110.31 (2013): 12738-12743.
Vrijenhoek, RC. "An allele affecting display coloration in the fish, Poeciliopsis viriosa." The Journal of heredity 67.5 (1975): 324-325.