Glofish zebra danio and other artificially colored fish

The fish found in pet shops are typically young specimens that have not yet displayed their full potential beauty. It is a well-known fact that customers tend to “buy with their eyes,” a principle that also applies to aquarium inhabitants. As a result, less attractively colored species often face challenges in sales, especially those that take longer to mature and reveal their vibrant colors. Rainbow fish exemplify this phenomenon; while they are undoubtedly the most colorful freshwater fish, their juvenile forms resemble mere herring, garnering little attention in pet shops. To adhere to the straightforward principle that colorful fish are more likely to attract buyers, Asian breeders were pioneers in the production of artificially colored fish. This practice began with the coloring of the Indian glassy fish. Nowadays, candy-colored specimens of this species are seldom found in Polish pet shops, having been supplanted by glofish zebra danio and several other fish species displayed in bright, unnatural hues. These fish are genetically modified, and if you reside in the European Union, it’s important to understand why you should think twice before purchasing them.

Why do glofish glow?

Geneticists have isolated the gene responsible for synthesizing green fluorescent protein (GFP) from the jellyfish Aequorea victoria, which enables fluorescence. Given its observability and non-toxicity to living organisms, GFP has found application in molecular biology. Further research has led to the discovery of similar proteins from various organisms, which have undergone numerous modifications. These modifications increased luminescence intensity and altered the wavelength of emitted light, resulting in proteins that glow in blue, pink, green, violet, yellow, and red.

How was glofish zebra danio developed?

In 1999, Dr. Zhiyuan Gong and his colleagues at the National University of Singapore introduced the gene responsible for synthesizing the green fluorescent protein into the genome of the zebrafish. This resulted in a fish that glowed brightly under both natural white light and ultraviolet light. The researchers aimed to create a bioindicator capable of detecting contaminants by fluorescing in the presence of environmental toxins. The goal was to obtain a normal-looking danio that would begin to glow when exposed to toxins in water. Soon after, the same team developed a line of red fluorescent danios by adding a gene from an anemone and a line of yellow fluorescent danios by incorporating a variant of the jellyfish gene.

Subsequently, a team of Taiwanese researchers, led by Professor Huai-Jen Tsai, succeeded in producing a fluorescent green Japanese rice fish (Oryzias latipes). The reasons for selecting danios and rice fish lie in their status as model organisms utilized in scientific research.

From the lab to pet shops

The genetically modified fish quickly gained licensing from two companies—one in the United States and another in Taiwan. By 2003, the glowing rice fish entered the pet market in Taiwan, yielding substantial profits, while the glofish zebra danio followed suit in the United States.

Currently, various glofish are recognized, including:

• zebra danio (Danio rerio)
• betta (Betta splendens)
• Sumatra barb (Puntigrus tetrazona)
• rainbow shark (Epalzeorhynchos frenatum)
• bronze catfish, (Osteogaster aeneus) before Corydoras aeneus
• zebra cichlid (Amatitlania nigrofasciata)
• X-ray fish (Pristella maxillaris)
• angelfish (Pterophyllum scalare)
• Japanese rice fish (Oryzias latipes),
• black tetra (Gymnocorymbus ternetzi).

Transgenic organisms

Living organisms, both animal and plant, whose genomes have been modified through genetic engineering methods, are referred to as transgenic organisms (genetically modified organisms or GMOs). The marketing of GMOs is regulated by applicable laws. In the European Union, GMOs are not authorized for sale. Consequently, the sale, possession, and propagation of glofish are illegal. This restriction also extends to hybrids created by crossing a glofish with a non-GM species. For insights into the topic, you need to investigate legal regulations of your country.

Artificially coloured fish

While genetically modified fish may not directly suffer from the modifications themselves, the methods used for chemically coloring fish can be classed as a form of animal abuse. Here, I will focus on the procedures employed for artificially coloring fish. By understanding the darker side of aquaristics, you will be better equipped to make informed purchasing decisions. Remember that consumer demand fuels supply.

What is chemical fish coloring?

The procedures involved in fish coloring are often shrouded in secrecy. However, it can be assumed that each culture has developed its own techniques to produce a large number of artificially colored fish while minimizing losses. Unfortunately, quantifying the percentage of fish that perish after being subjected to dye treatment poses a significant challenge.

The dye is typically introduced into the fish’s body via injection. This process requires removing the fish from the water, which is inherently stressful, and then administering precise injections at specific points on the body—in the case of the Indian glassy fish, on its dorsal and ventral sides. Achieving the desired color effect often necessitates multiple injections. Close examination of stained specimens has revealed that the dye remains liquid under the fish’s skin, suggesting that its presence may not be inert and could potentially poison the fish over time, impairing the function of its internal organs. The stress of injection and the risk of disease transmission (as fish are injected using the same needle) contribute to a significant number of individuals developing health issues post-treatment. Studies on dyed Indian glassy fish have shown that over 40% were infected with the lymphocystis virus, compared to only 10% in untreated fish, although dyed fish often display no visible symptoms.

Additionally, tattooing procedures are performed using a syringe filled with dye and a needle on light-colored fish, as well as albino or xanthoric varieties. Commonly tattooed species include parrot cichlids, kissing gouramis, and silver mollies, often bearing indistinct patterns such as dots, spots, hearts, flowers, or lettering.

The resulting colors may fade over time. Although reports from hobbyists indicate a range of six to twelve months for the color to diminish, some assert that certain fish do not lose their colors, likely due to variations in dye formulation.

In addition to injections, fish baths in dye solutions are also employed, leading to significant mortality rates among those fish subjected to this treatment.

Color-enhancing foods

The only safe and natural method for enhancing the color of fish is through a diet rich in natural pigments from the carotenoid group. Fish can be fed color-enhancing foods that include high levels of carotenoid-rich ingredients, such as krill, shrimp, red peppers, spirulina, and more. For insights on how carotenoids work and their importance in a fish’s diet read How do carotenoids affect fish coloration? It is essential to remember that factors such as water parameters, aquarium design, stocking density, and suitable companion species also influence fish coloration.

Buy wisely

With the vast array of species and remarkably attractive breeding forms available, it is unnecessary to opt for unnatural-looking fish. Responsible aquarists who view fish as living beings rather than mere objects will refrain from purchasing specimens with gaudy, artificial colors. Additionally, those new to the hobby should be counseled by experienced aquarists to avoid acquiring such fish.

Ph.D.Eng Aleksandra Kwaśniak-Płacheta