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Glofish or Zebra Danios?
(Brachydanio reri)


zebra danios, glofish, Brachydanio reri

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And Man said, “Let there be Glofish.” 

Glofish do not exist in nature. They were created in a laboratory. No, you are not seeing things. You may not read about it on the front page of USA Today. You may not hear about it on a television commercial break that ends with the words, “film at 11.” BUT… whether you realize it or not there have been over 660 patents issued on biogenetically engineered animals in the USA alone. And that number is increasing at an alarming rate every year. Transgenic animals are being patented like latest feature on a microwave oven or the next generation of digital music player. The difference is that here we are talking about living, breathing organisms rather than motherboards and microchips.

The Golfish just turned 10 years old. Happy birthbay! Just a decade ago there was no such thing as a Glofish. What exactly would be the purpose for making a fish glow? Good question! Believe it or not, the answer was not to strike it rich because every aquarium owner on the planet will feel the need to rush out and buy one. The Glofish was created to answer a higher calling.  For Dr. Zhiyuan Gong and his colleagues at the National University of Singapore (NSU) the goal was quite simple, and perhaps even noble. The idea was to genetically engineer a fish that would glow when it came into contact with environmental toxins in any freshwater ecosystem. A fish that detects and by default identifies the manufacturing facilities and corporations that are poisoning our planet’s most valuable resource, how cool is that? Do you think it was a sheer coincidence that the first Glofish ever created was GREEN?

Selective bioluminescence, this is indeed a lofty goal. Exactly what is involved in creating a species that is biologically designed to help save the planet? The logical answer is that you must first find a way make an animal glow. Only after the objective of bioluminescence is achieved, can you address the problem of biologically triggered selectivity.

These were the problems faced by bioengineering team in Singapore a decade ago. Of course before you can make a fish glow, you must first have a fish. The team settled on the Brachydanio reri, a species endemic to East India, more commonly referred to as a zebra danio or zebrafish because of its horizontal striping. Why choose a fish that isn’t indigenous to Singapore? This could have been strictly a matter of convenience. Most of the world’s supply of this popular minnow variety is raised on fish farms, one of which is located in Singapore. Acquisitioning a batch of fish eggs for scientific research would seem preferable to a bunch of geneticists wading around in streams with fish nets in hand. This may or may not have been a determining factor in the selection process.

The next step was to infuse a zebrafish embryo with GFP (Green Fluorescent Protein) and allow it to incorporate into the zebrafish’s genome. GFP is a gene found in the species Aequorea victoria, more commonly known as crystal jellyfish. It produces a bright green bioluminescence. The experiment was a success. When injected into a zebrafish embryo, the addition of GPF produced a hybrid fish that absorbed and then readmitted light from the green spectrum. A variant of this jellyfish gene caused the resulting offspring to fluoresce yellow. RFP (Red Fluorescent Protein) derived from sea coral of the genus discosoma created zebrafish that luminescence in red. While this scientific feat was amazing in and of itself, it was only the first step in creating a fish that would actually glow when exposed to toxic waste material. What they did create, however, was a previously nonexistent transgenic species that would go on to spark controversy around the world.

Just a few short decades ago, microwaves and VCRs were competing for the number one hotspot of must have gadgets in the marketplace. There was no such thing as a cell phone or an ipod. The world’s top techno-giants continually compete for their market share in the latest new gadget technology has to offer. Whenever there is something new that can have a dollar value attached to it there will be someone, somewhere that will find a way to package and sell it.

The creation of the world’s first florescent fish was bound to draw some attention. It did not take long for news of NUS’s success to reach the desks of entrepreneurs Alan Blake and Richard Crockett. They immediately recognized the commercial viability of these biogenetically engineered fluorescing fish. But the mass marketing of a genetically engineered living organism to the public was virgin territory. This thought did not daunt the future “biopreneurs” of Yorktown Technologies. Fortunately for Blake and Crockett, fish farms for the production of zebra danios had been in existence in the southern parts of United States since as early as the 30s. It was not much of a leap to raise a species that is only a single gene removed. Contracts were drawn up and Yorktown Technologies was awarded sole distributorship of genetically modified zebrafish for the entire planet. Austin, Texas became the new home for the first fluorescing fish ever created by man, a.k.a Glofish.

Biogenetic Menace or Needless Paranoia?

You might think that the marketing of a novelty item (even one that is genetically engineered) within the booming aquarium trade industry would be of little national interest. Think again! The gene that was inserted into zebrafish to make them fluoresce was immediately deemed a drug. As such the environmental risk assessment of the proposed commercial distribution of Glofish fell within the jurisdiction of U.S. Food and Drug Administration. Yorktown Technologies complied with two years of extensive environmental risk assessment research and consultation with various State and Federal agencies to procure the right to sell these fish to the public. In Dec. 2003, the FDA ruled that since Glofish are not designated to be part of the nation’s food supply they did not fall within their jurisdiction. Yorktown Tech was summarily granted the right to move forward at the federal level. The state of California, however, was not convinced.  They did back down from their original stance and agreed to allow the sell of Glofish if Yorktown submitted to more extensive research in the area of risk assessment. Unfortunately, said research would cost hundreds of thousands of dollars and take years to complete. Glofish have been sold in 49 of the 50 states in the U.S. since Dec. 2003. The sell or possession of Glofish is still illegal in the State of California.

But how would the rest of the world react to the idea of a genetically engineered organism being unleashed on the general public? Is this just an ultra-cool novelty item predestined to become a favorite among aquarium owners around the world? Or are we in fact letting a bioengineered genie escape from the bottle never to be returned?  Once you allow the sell of a single transgenic organism on the open market the precedent has been set. Glofish could just as easily be construed as Frankenfish as they could be perceived as harmless new variety of aquarium fish.

Many nations had already foreseen the eventual marketing of biologically manipulated organisms and had enacted legislation to prevent such an “atrocity” from ever happening. Those that did not took swift and decisive action. Even before Golfish were available for sale they were banned in Europe, Japan, Australia, and Canada despite the over two years of extensive ecological risk assessment studies preformed by Yorktown Technologies. Who would have thought something as benign as an ornamental aquarium fish would create such a stir?

Aquatic Invasive Species & the Environment

Bioengineered transgenic manipulation aside, environmentalist have long expressed concern over the potential ecological ramifications of nonnative species being intentionally or even accidentally introduced to an established ecosystem. The sell of piranhas is illegal in most of the United States and much of the world for this very reason. The fear that one of the most predacious species in existence will suddenly and irreversibly establish itself as the number one predator at the top of the food chain out weights any perceivable benefit of allowing them to be raised by home hobbyists. Common sense dictates that this is perhaps the most extreme example one could come up with. While this is true, the sell and ownership of piranhas was legal in the U.S. until piranha specimens were discovered in the wild most likely after their intentional release because they had outgrown their fish tanks.

There are document case studies on the impact of much more seemingly innocuous fish being introduced into previously uninhabited ecosystems. One such example is the plati fish (Xiphophorus maculates). The plati is native to Mexico. This species is particularly well suited for slower moving freshwater systems such as canals, ditches and warm springs. They have established significant populations in the United States in the canal systems of Tampa Bay and Gainesville, Florida. They have become naturalized in the state of Montana. They have also acclimated to the freshwaters of Columbia, Singapore, and Hong Kong. Hong Kong ecologists report that these “illegal aliens” are creating an adverse impact on their aquatic ecosystems due to the plati’s prolific breading habits.

The plati’s genetic cousin, the swordtail (Xiphophorus helleri) is another popular aquarium fish native to the Western Hemisphere. Feral swordfish populations now exist in both Africa and Australia. Once established, these fish reproduced at such an alarming rate that their presence is threatening the indigenous freshwater species on both continents. Yet another example is the tilapia. Tilapia, a cichlid native to the Amazon River Basin, has been deemed a nuisance species in the southern US after populations sprang up from out of nowhere. All three of these species invasion of non-indigenous territories are aquarium trade related. Fish are not like an item in your local supermarket. Once they have made their way into the wild they can’t be subject to a product recall and quickly pulled off the shelf.  

What Does This Have to Do With Glofish?

Do Glofish pose a threat? The end of World War II marked beginning of an explosion in the aquarium trade industry. Over 200 million of these fish have been imported and sold in the U.S. alone over the past half century. In a day and age when both regional and national governmental agencies have no choice but to develop and implement AIS (Aquatic Invasive Species) management systems there has only been single instance of zebra danios successfully establishing a reproducing population in the wild. This population established itself in Columbia, coincidentally close to a fish farming facility that rears zebrafish for exportation.  Zebrafish are incapable of surviving the temperate water conditions in all but the most southern states. To date, there has not been a single report of an established reproducing population in the wild anywhere in the United States. Only a single gene differentiates Glofish from their natural counterpart, zebra danio. If zebrafish, accidentally or intentionally introduced into the wild, posed a quantifiable ecological threat to the planet’s freshwater ecosystems that threat would have been apparent long before geneticists infused a fluorescing gene into their genome. Yet glofish remain one of the most illegal pets ever to be sold on the open market. Ironically, fluorescing fish have become top sellers in the aquarium trade in most of Asia and in the U.S.

Since Glofish went on sale in 2003, scientists have successfully incorporated the fluorescing gene into rabbits, pigs, dogs and cats. The transition to mammals was undoubtedly inevitable. Given the rate of scientific progress perhaps it is understandable why many nations around the world decided it prudent to outright ban transgenic organisms for any purpose other than scientific research. Keeping the genetic genie tightly sealed in its bottle might just be the wisest course of action.  I’m not sure how I would react if I suddenly realized that my daughter’s cat just gave birth to a litter of kittens that glowed under a black light. Although I’m willing to bet that she would think it was the coolest thing since Sponge Bob Square Pants. Fish, on the other hand, can not impregnate an entire neighborhood if left to prowl freely.  While the sale of a genetically altered fish simply because they look prettier than their "natural" counterparts may be ethically questionable, they are strikingly beautiful fish. It almost begs the question, “How many times have you upgraded a cell phone in perfect working order simply because the new model looked cooler, was more compact, or everyone in the office had a newer model than yours?”

Fluorescing fish are the first and might very possibly go down in history as the only genetically modified animals ever to be commercially sold as pets, at least in the immediately foreseeable future. Fifty years from now, however, not having a dog or a cat that literally glows in the dark might be considered extremely old fashion or possibly even irresponsible pet ownership. I’ll leave that up to the future to decide. As for me, it’s time to call this a wrap. I have to feed my Glofish.

Zebra Danio (Brachydanio reri)


Zebra danios are a member of the Cyprinidae family. They are native to eastern India. Zebra danio are hardy and active fish with peaceful temperaments. They make excellent additions to a community tank provided they are housed with fish of similar size and temperament.

Zebra danios have a five year life span and will grow to length of about two inches. They thrive in slightly acidic to neutral water (pH 6.5-7.0) and prefer a rather chilly water temperature of 64-74 degrees Fahrenheit. They can, however, adapt to the warmer climate needed for most other tropical fish. They are surface dwelling fish that favor moving water. Zebrafish are shoaling fish. It is not advisable to purchase a single fish for your aquarium. Nature intended them to live in a community.

Zebrafish are omnivores that can survive just fine on a diet of tropical fish flakes.

In their genetically unaltered state it is easy to tell the males form the females. Males have blue and gold stripes. Females have blue and silver stripes. The female tends to be larger and fuller bodied than the male. This would be the distinguishing factor in the genetically altered varieties.

Breeding Frankenfish


Zebra danios are some of the easiest fish to breed in captivity. Spawning can be triggered by raising the water temperature up a few degrees near dawn. This will trick the fish into believing it is mating season. When spawning occurs 3-500 eggs will be scattered across the breeding tank floor. Remove the adults to prevent them from eating the eggs.

The fry will hatch in 2 days. They can be fed liquid fry food or small amounts of powdered eggs. In a week or two they will be large enough to eat brine shrimp or finely crushed tropical fish flakes.

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