By Carol McCarthy

Fireflies flicker and flash as they dart through their mating dances, all the while transforming a lovely summer night into a magical evening. While the bioluminescence that allows these insects to glow and gain the moniker “lightning bugs” creates wonder in humans, it is a not-uncommon feature in the animal world, especially for fish and other marine species.

National Geographic defines bioluminescence as light that occurs from the reaction between two chemicals within a living organism: the compound luciferin and either luciferase or photoprotein. The ability to produce light is not just a flashy feature; bioluminescence can give the animal a competitive advantage. For example, deep-sea vampire squids eject glowing mucus to startle predators, and hatchet fish use light-producing organs to adjust reflections off their bodies, masking themselves to prey who are hunting them from below. Other animals that glow or flash to get ahead at sea and on land include plankton, coral, and glowworms.

For decades, scientists and medical researchers studied bioluminescence in nature and have adapted fluorescent genes as biomarkers for many applications. That is how GloFish found their way into home aquariums across the country.

Scientists in Singapore were the first to genetically modify fish to fluoresce. The long-term goal for the scientists was to detect toxins in water so that polluted waterways could be identified and the local communities using those waterways could be protected.

“The first step was to make them fluoresce all the time,” explains Alan Blake, co-founder and CEO of Texas-based Yorktown Technologies, which introduced GloFish to the home aquarium market in 2003. “The eventual goal was that they would selectively fluoresce in the presence of toxins,” he said.

Yorktown Technologies purchased the license to those always-fluorescing fish and bred its first fluorescent aquarium pet, the Starfire Red Danio, in 2003. Today there are 12 lines—species and color combination—of GloFish, including tetras, zebra fish, and barbs, in such colors as Electric Green, Moonrise Pink, and Cosmic Blue.

The fish appear bright under normal white light and fluoresce brilliantly under a blue light. They are also quite striking under black light in a completely darkened room.

Since their introduction, Blake says the fish have created excitement in the home aquarium world, with children especially fascinated by them.

GloFish now comprise “roughly ten percent of all aquarium fish industry sales,” said Blake, noting that number includes both GloFish-branded products and non-GloFish products sold along with the fish.

Before GloFish could be sold legally in the United States, they had to pass regulatory muster as genetically modified animals with the federal FDA, which worked in coordination with the USDA and U.S. Fish and Wildlife Service, as well as with various state regulators. The state of California initially balked at the idea of transgenic fish, but in 2015 reversed course and allowed aquarium owners to buy and keep them.

Initially, there were misconceptions and misunderstandings. Some environmental scientists were concerned that the fish could harm local wild populations if released by pet owners. However, the tropical fish cannot survive in North American waters.

“Their non-GloFish equivalents have not established in the wild, and it is reasonable to assume that a bright, fluorescent equivalent would have even less of a chance of survival,” says Craig A. Watson, director of the Tropical Aquaculture Laboratory at the University of Florida. “These are little fish that are prey for larger fish.”

“It’s like a big neon sign saying ‘eat me,’” Blake says of the disadvantage of being a bright, fluorescent fish in an environment chock full of predators.

Even if they are released into the wild, the fluorescent gene does not stay in the population, according to an extensive study by Purdue University. Traditional zebrafish consistently beat out their glowing counterparts when it came to winning mates, the study found. There also is no evidence indicating the fluorescent genes from GloFish are transferred to any other species, Watson says.

Marine biologists and environmental scientists rarely, if ever, agree, he notes, but after more than a decade in circulation, Watson can think of no issues in the wild created by GloFish. “If there had been any, I am sure it would have been widely reported,” he says.

“There will always be purists within the hobby who don’t even like fancy strains, such as long-fin, albino, etc., natural mutations that are common within many domestic fish. Those people probably will never buy a GloFish,” says Watson. “However, a LOT of people love them.”

George Goulart, owner of Aqua-Life Central, a fish and aquarium store in Providence, R.I., is one of those purists. He carries GloFish, but they are not his favorite and he says he sells more of the traditional black tetra fish.

“They are very popular because of the colors,” says Goulart, who has 40 years of experience in the fish and aquarium business.

He says some aquarium owners buy fish by appearance, simply for decoration without knowing anything about the species, and he tries to educate them. He thinks the impulse to jazz up their aquariums is what prompts people to purchase GloFish.

Blake says education about the fish is important, as the public sometimes falsely believes GloFish are dyed or injected with color, while they are actually bred to glow.

“We say they are born brilliant,” Blake notes. “A gene is inserted in one fish embryo one time, and the fluorescence trait is then carried from generation to generation through traditional breeding.”

The fact that they are not dyed or injected is the reason Goulart will carry them in his store. He says he will not sell fish that are dyed or injected.

“It’s not healthy for them; it affects all their systems,” he says of dying and injecting fish. But those health concerns do not apply to GloFish, he says. “It’s just the skin that changes color. It doesn’t affect their systems,” Goulart notes.

When it comes to the care of GloFish, their needs are the same as their duller freshwater brethren regarding tank size, water temperature, food, etc. Life spans average from 3.5 to 5 years, comparable to the average life span of tetras and many other aquarium fish.

As GloFish make a bright splash in aquariums around the country, will we soon be seeing other glowing species on the horizon? Blake says he does not expect pet owners to start clamoring for a hot-pink poodle anytime soon.

“There are a lot of marine fish that have bright colors and a couple hundred [non-fish] species that are actually fluorescent. I think because of this, GloFish look natural to people. A fluorescent dog or cat would not look natural and would not likely be something people would want,” he says.

Image: Build Your Aquarium, GloFish.com

You can learn more about the science of GloFish at the official GloFish site.

Ready to buy a GloFish of your own? You can find them locally here.

mucus A type of slime that is made up of certain salts, cells, or leukocytes

impulse A wave that is transmitted through nerves and nervous tissue

embryo The zygote that is developed after conception