Are all GloFish injected?

GloFish are a genetically modified brand of fluorescent fish that come in bright colors like Electric Green, Starfire Red, and Cosmic Blue. They were originally created by scientists in Singapore in 1999 by inserting genes from coral, sea anemones, and jellyfish into zebrafish embryos. This genetic modification allows the fish to naturally glow under black lights.

GloFish quickly became popular in the aquarium trade and were introduced commercially in the United States in 2003 by Yorktown Technologies. They were initially only allowed to be sold in a few states, but are now available in pet stores across the country. With their bright, neon colors, GloFish provide a unique pop of color to home aquariums.

But how exactly are these fluorescent fish created? Are all GloFish genetically modified through injection or are there natural breeding populations? This article will explore the science behind how GloFish are made and examine whether all GloFish available to purchase have been genetically altered.

The Creation of GloFish

All GloFish start out as non-fluorescent zebrafish embryos. Zebrafish are a common species used in genetic research because their embryos are transparent, allowing scientists to easily manipulate their genes.

To create the GloFish brand, scientists inject the zebrafish embryos with DNA from other organisms that naturally glow, like sea coral and jellyfish. This injected DNA incorporates into the embryo’s genome and is passed onto future generations of fish. However, the fish cannot pass their fluorescent genes to other wild species because they are unable to breed with other types of fish.

The most commonly used gene in creating GloFish is from sea anemones and produces red fluorescence. Other genes added produce fish in green, orange-yellow, blue, and purple hues. The fluorescent protein genes are added along with an antibiotic resistance gene to help identify which embryos take up the new DNA.

The injection process

The injection process uses micropipettes to insert the engineered DNA into hundreds of single-cell zebrafish embryos. Each embryo is individually injected in a delicate procedure. Only a very small percentage of injected embryos integrate the new genes into their genome and survive to become fluorescent fish.

The embryos that successfully incorporate the genes are grown to adulthood and bred to produce offspring that reliably express the fluorescent traits. The original GloFish lines were maintained by continuously breeding the genetically modified fish.

Every GloFish available today can be traced back to the original lines of zebrafish genetically engineered with coral and jellyfish DNA in Singapore. No natural populations of fluorescent zebrafish exist.

Regulation of GloFish

GloFish spawned controversy when they were first marketed because they were the first genetically modified animal to be sold as pets rather than for research or food. Criticism surrounded the unknown environmental impacts if the fish ever escaped into natural waters.

In response to ethical concerns, the U.S. Food and Drug Administration (FDA) thoroughly tested the GloFish and confirmed they are just as safe to eat as unmodified zebrafish. The FDA also found no evidence the genetic modifications would harm the environment since released GloFish could not breed with wild populations.

While safe for the environment, the FDA ruled they could only be sold for ornamental purposes and not for human consumption. Today, the FDA provides strict regulation on the breeding, production, and sale of GloFish.

GloFish facilities

All GloFish are bred and raised under close monitoring at the GloFish breeding facility in Florida. No natural populations exist in the wild. The Florida facility maintains the original genetically modified breeding lines of zebrafish and produces juveniles for distribution to pet stores.

The GloFish Facility has high biosecurity measures and follows FDA regulations to prevent any accidental release of fish. Water from the facility does not flow into natural streams or rivers, providing containment. The facility was designed so the GloFish could not influence natural ecosystems.

Breeding GloFish

While the major GloFish production occurs at the regulated Florida facility, the fluorescence trait allows hobbyists to easily breed the fish at home. GloFish pass on their engineered fluorescent genes to their offspring.

Breeding pairs of GloFish will produce broods of fry with about 50% exhibiting the bright fluorescent colors. The others will lack fluorescence due to normal genetic shuffling during reproduction. Only the fluorescent offspring should be kept and raised.

Successfully breeding GloFish requires carefully pairing males and females that exhibit the desired color. Some specialty pet stores may also offer breeding trios consisting of one male and two females in a color pattern.

Setting up a breeding tank

Special care must be taken when breeding GloFish to maximize the chances of success. A separate 10+ gallon breeding tank should be established with the following features:

– Fine gravel substrate free of sharp rocks
– Several live plants like java moss, elodea, or hornwort
– Dim lighting and/or floating plants to provide shade
– No filter or a gentle sponge filter
– Water temperature around 82°F
– No aggressive tankmates like bettas or cichlids

The breeding tank should be cycled for at least 2 weeks before adding the adult fish. Perform regular water changes to keep nitrates low. The parents-to-be should be well fed a variety of foods and live foods prior to breeding.

Spawning behavior

When ready to spawn, the female will display a protruding ovipositor and fuller abdomen. The male will actively chase and nip at her sides. Spawning typically occurs in the morning within the first two hours of light.

The fish will align in an embrace, wrap their bodies around each other, and lay approximately 50-100 eggs. The adults should be removed once spawning concludes so they do not eat the eggs. The eggs will hatch in 24 to 36 hours.

Raising the fry

The tiny swimming fry initially feed off their attached yolk sacs for 2-3 days before becoming free-swimming. They should initially be fed powdered fry food or infusoria several times a day. Crushed up flakes can be fed after a week.

The juvenile fish grow rapidly and may start displaying their fluorescent colors at 6-8 weeks. Separate the brightest individuals for breeding the next generation. Fluorescence will increase as they mature.

GloFish Fry Care
Days 1-3 Live off yolk sac attached to abdomen
Days 3-7 Feed powdered fry food 3-5 times daily
Week 2 Feed crushed flakes 2-3 times daily
Week 6-8 May begin displaying bright colors

Buying GloFish

GloFish can be purchased at many pet stores across the United States and are occasionally available for shipping online. They come in a variety of fluorescent colors with new varieties still being developed.

The standard colored strains available are:

  • Starfire Red – Bright red-pink
  • Electric Green – Vibrant green
  • Cosmic Blue – Cyan blue
  • Galactic Purple – Violet purple
  • Moonrise Pink – Pale pink
  • Sunburst Orange – Orange-yellow
  • Dazzling Blue – Bright blue

Some big chain pet stores like PetSmart and Petco may have a limited GloFish selection, while smaller local fish stores have a wider array. When purchasing, look for active fish with full, bright colors devoid of any spots or blemishes.

GloFish are schooling fish, so buy groups of at least 6. Mix colors for a more brilliant aquarium. Prices average around $5 per fish for the common colors and up to $10-$15 for rarer varieties.

Spotting problems

Avoid any GloFish with the following signs of poor health:

– Pale or faded colors
– White spots or gold dusting on skin
– Clamped fins
– Bloated or sunken abdomen
– Rapid breathing
– Lethargy and loss of appetite

These signs may indicate disease, parasites, or stress. Only purchase fish showing nice coloration and actively swimming. Make sure the aquarium at the store has clean water and healthy tankmates.

Caring for GloFish

Caring for GloFish is similar to keeping zebrafish. A 10+ gallon cycled and filtered tank is recommended with these water parameters:

  • Temperature: 72°-82°F
  • pH: 6.8-7.5
  • Hardness: Very soft
  • Nitrates: Under 20 ppm

Perform 25% weekly water changes and feed a variety of flakes, pellets, frozen, and live foods. They enjoy lots of plant cover provided by live plants or silk plants. Though technically tropical fish, they tolerate a wide temperature range.

Tankmates should include other peaceful community fish that thrive in soft water like neon tetras, white cloud mountain minnows, hatchetfish, and bristlenose plecos. Avoid aggressive fish like tiger barbs that may nip fins.

GloFish have an average lifespan of 3-5 years with proper care. Their bright colors will need to be replaced every few years through breeding or purchase of new stock.


Proper lighting brings out the full fluorescence in GloFish. Use a fluorescent black light positioned over the tank to make colors pop. Blue LED aquarium lights will also enhance their glow. Avoid intense white light that washes out fluorescence.

Place a UV sterilizer on the tank to further brighten coloration. These devices kill pathogens while emitting a violet glow that excites the fluorescent pigments. Lighting should be kept on for 10-12 hours daily.


In conclusion, all GloFish available for purchase originate from the first genetically engineered lines of zebrafish created by injecting coral and jellyfish genes into embryos. No natural populations of fluorescent zebrafish are found in the wild.

Strict FDA regulations require all GloFish breeding and production to occur in licensed facilities to prevent environmental impacts. Hobbyists can successfully breed the bright colors at home in conditioned breeding tanks.

When shopping for GloFish, look for active fish with full, vibrant colors. Avoid any specimens showing signs of illness like faded colors, spots, frayed fins, or rapid breathing. Be prepared to provide the proper soft water environment, schooling groups, plant cover, lighting, and care that GloFish need to thrive.

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