Banner: Depicts Cosmic Blue® Tetra. Photo used with permission.
This article was originally written for “Livebearers”, the journal of the American Livebearers Association, issue #230, Spring 2016.
Easily one of the most remarkable innovations in the tropical fish trade since the turn of the millennium was the advent of GloFish®, genetically engineered fluorescent zebra danios. These special little animals are zebra danios with a gene that creates a fluorescent protein derived from jellyfish added to their cells. This feature is genetic and heritable (although illegal to breed, as GloFish® are controversially trademarked). Three species are currently marketed in the United States, the zebra danio (Danio rerio), the black skirt tetra (Gymnocorymbus ternetzi), and the tiger barb (Puntius tetrazona). One other species has been created in Asia, the freshwater angelfish, (Pterophyllum spp.).
A question I have occasionally wondered myself is, why aren’t there more species of this remarkable fish available? Fluorescent varieties of the four most popular livebearers (guppies, mollies, swordtails, and platys) would certainly be a retail hit. I think the answer to this question lies somewhere in the process of genetically modifying fish. Currently marketed GloFish® are all egg layers that produce sometimes hundreds of eggs outside the body. This quality in particular is critical. The gene has to be added to a fertilized egg before it divides, in order that every cell in the fish’s body has that gene (needed for expression in the skin and inheritance in the offspring). With danios, tetras, barbs, and angelfish, eggs are readily available and following fertilization and the introduction of new genes; the embryos develop normally outside of the body. With livebearers, however, the process would be very different. Eggs would have to be surgically removed from a female, fertilized, genetically modified, and either artificially nurtured or transplanted into a surrogate mother until “birth.” Not a simple process.
Easily one of the most remarkable innovations in the tropical fish trade since the turn of the millennium was the advent of GloFish®, genetically engineered fluorescent zebra danios. These special little animals are zebra danios with a gene that creates a fluorescent protein derived from jellyfish added to their cells. This feature is genetic and heritable (although illegal to breed, as GloFish® are controversially trademarked). Three species are currently marketed in the United States, the zebra danio (Danio rerio), the black skirt tetra (Gymnocorymbus ternetzi), and the tiger barb (Puntius tetrazona). One other species has been created in Asia, the freshwater angelfish, (Pterophyllum spp.).
A question I have occasionally wondered myself is, why aren’t there more species of this remarkable fish available? Fluorescent varieties of the four most popular livebearers (guppies, mollies, swordtails, and platys) would certainly be a retail hit. I think the answer to this question lies somewhere in the process of genetically modifying fish. Currently marketed GloFish® are all egg layers that produce sometimes hundreds of eggs outside the body. This quality in particular is critical. The gene has to be added to a fertilized egg before it divides, in order that every cell in the fish’s body has that gene (needed for expression in the skin and inheritance in the offspring). With danios, tetras, barbs, and angelfish, eggs are readily available and following fertilization and the introduction of new genes; the embryos develop normally outside of the body. With livebearers, however, the process would be very different. Eggs would have to be surgically removed from a female, fertilized, genetically modified, and either artificially nurtured or transplanted into a surrogate mother until “birth.” Not a simple process.
Does this mean Glo-Guppies are a total fantasy? Maybe not after all. A paper (actually, two suspiciously similar papers from the same three authors) from 1976 explores the possibility of genetically altering Xiphophorus embryos via injection into the neural crest or embryonic yolk. While difficult, as technology improves, fluorescent livebearers might be possible.
More in the spirit of this column: if there are six fluorescence color genes that produce the different color varieties available (dubbed “Starfire Red®”, “Electric Green®”, “Sunburst Orange®”, “Cosmic Blue®”, “Galactic Purple®”, and “Moonrise Pink®”), how would they act genetically? Are they different alleles at the same locus, or different loci all together? The answer to that question depends on the method used by the engineers when creating GloFish® (I guess they didn’t have “pirate” basement geneticists in mind when creating their product). If the genetic engineers used a plasmid (a ring of DNA independent of the host’s DNA), than the different colors are different loci. If however, the geneticists tinkered with the fish’s chromosomal DNA, than most probably the different colors are different alleles of the same locus.
If it brings the reader any consolation, livebearers are already bioluminescent. No, the government hasn’t been secretly flooding the market with GMO fish; a 2014 study found Xiphophorus helleri is naturally green bioluminescent. Gives a whole new meaning to the name Green Swordtail! For more information on GloFish®, I recommend an article by Gerald Griffin: “GloFish Love them or hate them they are here to stay!” FOTAS Fish Tales Vol 5 Issue 4. tinyurl.com/glofisharticle
More in the spirit of this column: if there are six fluorescence color genes that produce the different color varieties available (dubbed “Starfire Red®”, “Electric Green®”, “Sunburst Orange®”, “Cosmic Blue®”, “Galactic Purple®”, and “Moonrise Pink®”), how would they act genetically? Are they different alleles at the same locus, or different loci all together? The answer to that question depends on the method used by the engineers when creating GloFish® (I guess they didn’t have “pirate” basement geneticists in mind when creating their product). If the genetic engineers used a plasmid (a ring of DNA independent of the host’s DNA), than the different colors are different loci. If however, the geneticists tinkered with the fish’s chromosomal DNA, than most probably the different colors are different alleles of the same locus.
If it brings the reader any consolation, livebearers are already bioluminescent. No, the government hasn’t been secretly flooding the market with GMO fish; a 2014 study found Xiphophorus helleri is naturally green bioluminescent. Gives a whole new meaning to the name Green Swordtail! For more information on GloFish®, I recommend an article by Gerald Griffin: “GloFish Love them or hate them they are here to stay!” FOTAS Fish Tales Vol 5 Issue 4. tinyurl.com/glofisharticle