Home | Aquarium Livestock | GloFish – It’s All in the Genes

GloFish – It’s All in the Genes

Electric Green Tiger BarbsGloFish are some of the most popular, colorful and controversial fish to enter the aquarium trade in a long time. Their easy care, small size, peaceful nature and neon bright colors make them appealing to aquarists of all ages, but the modifications that cause these bright colors cause some debate among aquarists, scientists and environmentalists alike.

The original “GloFish” were not created for the aquarium trade. They came from a popular fish used in many different fields of research, the Zebra Danio (Danio rerio). Zebra Danios have been used in research for environmental studies, cancer research, genetics, reproductive biology, neuroscience and applications to other fields as well. They even made the trip to space in 1975 on the Russian “Salyut 5” space station. So what makes them such good research subject? Zebra Danios are easy to breed and it only takes hours for the internal organs to develop after the eggs have been fertilized (about 24-36 hours, depending on temperatures and conditions). During this time, it is easy for researchers to monitor the development of the embryo since the “shell” around the eggs is a clear membrane. The eggs can hatch about 12-36 hours after that (again, depending on the conditions). These variable time frames also mean that, while the development is being studied, conditions can be adjusted to slow down or speed up the development, depending on what exactly the researchers are trying to determine. The genetic sequence involving the structure of the Zebra Danio’s DNA and RNA is very well-known at this point and is comparable enough to our own that, by understanding how changes in this structure affect the fish, researchers are gaining more understanding into how changes in our genetic structure can affect our own health.

Originally, GloFish were being developed for two major fields: cancer research and pollution detection. In the late 1990’s/early 2000’s, researchers thought to develop a fish that would change colors when a certain pollutant was found in their water. The thought was to develop a fish that would appear normal in “ideal” conditions but when a specific chemical or type of chemical was present in the water, a “trigger” would be set off to cause the fish to “glow” with a fluorescent protein in their bodies. As a step in this direction, they began to develop a fish that would always have this flourescent “glow” in a reproducible and hereditary way that wouldn’t affect the ecosystem around them. To do this, scientists turned to a fluorescent protein naturally found in jellyfish, corals and anemones rather than potentially harmful chemical dyes. Around the same time, similar projects were using a fluorescent protein to “mark” specific genes that were thought to be a cause or sign of cancer. By pairing the fluorescent protein with the cancer-related gene, researchers could see the fluorescence increase or decrease along with the other gene and see if an increase or decrease in that gene was related to the cancer. Since the genes (and cancers) in these fish behave in much the same was as they do within ourselves, researchers are using this to develop a way to track, diagnose and treat cancer in people.

A few interesting things happened as these trends in research progressed. The protein they are injecting into the eggs at the start of their development didn’t appear to be affecting their development or care. The fluorescence was passing along to the offspring and the offspring’s offspring. Different color proteins were giving the fish different fluorescent coloration and the resulting fish looked kind of cool.


Enter…The GloFish

Galactic Purple DaniosThe GloFish in the aquarium trade are bred, trademarked and sold to distributors by Yorktown Technologies, a company out of Austin, Texas, although different types of similarly modified fish were sold in Asian (particularly Taiwan) under different brand names. The original GloFish were genetically modified Zebra Danios with a red glow from the Red Fluorescent Protein (RFP) found in Discosoma sp. mushroom anemones and with a green glow from the Green Fluorescent Protein (GFP) found in the jellyfish Aequorea victoria.

More colors and species have been developed and modified over the past several years. A yellow-orange type coloration emerged from Yellow Fluorescent Protein (YFP), a mutation from the GFP and blue and purple fish have appeared, the source protein I was not able to identify for this blog. Other fish have been added to the GloFamily, including the Electric Green GloBarb (from the Tiger Barb, Puntius tetrazona) and the GloTetra (from the Black Skirt or White Skirt Tetra, Gymnocorymbus ternetzi). These new varieties are currently available in Electric Green, but Sunburst Orange and Moonrise Pink are being released mid-May 2013.

GloFish can be kept in a normally-lit aquarium, but the fluorescence will really pop under a black light or actinic (purple-blue) light.  Overall, their behavior and care is the same as the natural Zebra Danios, Tiger Barbs or Black/White Skirt Tetras. The fluorescent protein takes more metabolic energy from the fish, so GloFish tend to stay slightly smaller than the unmodified counterparts. Since they need to expend energy on the fluorescence, they can also be slightly more vulnerable to disease or improper or poor water conditions.


The Controversy and Ethics

Moonrise Pink TetraAs with any other “modified” animals in the pet trade, these fish have seen their share of controversy. Modified fish are certainly not new to the hobby. Even hundreds of years ago, fish were being selectively bred for their appearance, fancy goldfish being the classic example.  Designer clownfish are a more recent fad in saltwater aquaria. While the color changes are induced in the GloFish by injecting the protein, the goldfish and clownfish are selectively bred to promote naturally-occurring mutations like abnormal color, bulging eyes, stunted growth or other features.


Some opponents of GloFish compare their alteration to the practice of dyeing or tattooing fish to change their color. The GloFish discussed here are not dyed. The change in the GloFish occurs in the embryotic stage of the first generation and is then passed on naturally to its offspring. Dyeing or tattooing to change color or pattern is modification done to otherwise natural adult fish. Some of these fish are tattooed or injected with a bright colors to change their outward appearance. Artificially dyed fish are exposed to a very acidic solution that removes their naturally protective slime coat, then dipped dye solution to change their color (in some ways like dyeing an Easter egg). Dyeing, injecting and tattooing are very harmful processes.  The survival rates are low, and the color result is usually not permanent, fading within a few months. GloFish color is permanent, passed on genetically, and doesn’t affect the health or behavior of the fish.



  1. avatar

    I want to know if you can grow a rainbow shark to the size of koi if its genetically modied.

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    Hello John, I don’t believe genetic modification has advanced to that point yet outside of science fiction and the SyFy Channel.

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    I do not see the reason to dye fish for sale. I can understand for research, but not for sale to the general public. What good are they except for children to look at under black light, which I consider stupid. Teach children what nature really is.

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    Hello Terry, That is certainly an ongoing debate within the aquarium industry and hobby. The industry is populated with captive-raised and aquacultured variations of freshwater and saltwater fish alike and has brought some natural species back from the brink of extinction. While these GloFish aren’t dyed, we did address the dying issue in an earlier blog Novelty vs Cruelty: The Ethics of Dyed vs Tattooed Aquarium Fish. We don’t promote or sell any harmfully altered or dyed fish here at That Fish Place – That Pet Place.

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    Are Glofish extinct?

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    Hello Jenna, GloFish don’t exist in the wild. They are all aquacultured and bred in captivity.

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    I can understand the controversy however this is capitalism at its finest. Why are they sold? Honestly, they are sold because they are awesome looking vs a black molly. Kids and adults alike enjoy something that is different and bright. It is like getting saltwater fish in an easy care freshwater environment. I have found them to be very easy to care for and hardy. I have had a 700 gal reef tank, 2.5 gal to 75 gal fresh water tanks. My 7 yo has a 10 gal (up from a pain in the arse 5 gal acrylic tank) with both these Glofish (3 Danios and 4 tetras) and neon tetras. I went looking as to why 1 of the 3 y.o. red Danio’s color is fading. All of the other fish are fine.

    If these bright colored fish are sparking an interest in aquatic life in the general public of kids I am all for it!!

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    I have a glofish whose eyes are like the first picture and the last picture of this article kind of translucent. However the other glofish in the tank their eyes are black. Is this normal and why is that?

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    Hello Nelly, Aside from some health issues that can cause cloudy eyes and lighting or camera flashes that can cause reflections, specific coloration would be a matter of genetics and breeding of that fish.

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    Terry, Glofish were NOT created just for sale. GloFish were originally bred more than ten years ago to help detect environmental pollutants. By adding a naturally derived fluorescence gene to the fish, scientists hoped to quickly and easily determine when a waterway is contaminated. The first step in developing a pollution-detecting fish was to create fish that would be fluorescent all the time. Scientists soon realized the public’s interest in sharing the benefits of this research, a process which led to GloFish fluorescent fish. To achieve their goal of helping to fight water pollution, scientists have developed a ‘switch’ that will cause always-fluorescing fish to selectively fluoresce in the presence of environmental toxins. A non-fluorescing fish will signal that the water is safe, while a fluorescing fish will signal trouble. To help further the research, a portion of the proceeds from sales of all GloFish goes directly to the lab where these fish were originally created.

    READ THIS IN IT’S ENTIRETY https://www.glofish.com/about/faq/#science

  11. avatar

    I like glofish

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    I think dying glofish is cruel, and it’s sad how society continues to destroy nature.

  13. avatar

    Hi Lulu, These glofish discussed here are not dyed and the genetic modifications and breeding practices used are safe and humane. For more information, you can visit the Ethics section of the GloFish company website.

  14. avatar

    It’s so very funny how you can explain to people over and over again that they are not dyed, but they still don’t get it. These fish were born with this color, which they inherited from there parents. It’s in the genes.

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    Hello, If you are looking for information on GloFish breeding, I would recommend visiting the GloFish website (www.GloFish.com) for more information.

About Eileen Daub

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Marine Biologist/Aquatic Husbandry Manager I was one of those kids who said "I want to be a marine biologist when I grow up!"....except then I actually became one. After a brief time at the United States Coast Guard Academy, I graduated from Coastal Carolina University in Myrtle Beach, South Carolina in 2004. Since then, I've been a marine biologist at That Fish Place - That Pet Place, along with a Fish Room supervisor, copywriter, livestock inventory controller, livestock mail-order supervisor and other duties here and there. I also spent eight seasons as a professional actress with the Pennsylvania Renaissance Faire and in other local roles. If that isn't bad enough, I'm a proud Crazy Hockey Fan (go Flyers and go Hershey Bears!).