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How do they create glofish?

GloFish are a genetically engineered type of fish that have been modified to express fluorescent colors. They were originally created by scientists in the early 2000s and have since become a popular aquarium fish. But how exactly are these glow-in-the-dark fish made?

The History of GloFish

The original GloFish were Zebrafish that had been genetically modified with jellyfish and coral genes to make them fluoresce under blue or ultraviolet light. This genetic engineering work was done by scientists at the National University of Singapore in 1999. Their goal was to create a fish that could detect pollution by glowing in the presence of toxins.

In 2001, the rights to market GloFish were purchased by Yorktown Technologies, a company in Austin, Texas. Yorktown rebranded the fish as ornamental pets called GloFish rather than as pollution detectors. By 2003, GloFish became the first genetically engineered animal to be sold as a pet when they were introduced to the US market.

The Genetic Engineering Process

To create a GloFish, scientists use a process called microinjection to insert DNA from a luminescent jellyfish or coral into the embryo of a Zebrafish. Here are the steps involved:

  1. Extract the luminescence genes from a jellyfish or coral.
  2. Inject the luminescence genes into fertilized Zebrafish eggs with a very fine needle.
  3. Screen the injected embryos for those that have integrated the new DNA and are expressing the fluorescent protein.
  4. Breed the fluorescent Zebrafish to create a transgenic line that passes on the genetic modification.

The injected jellyfish and coral genes cause the Zebrafish to produce green, red, or orange fluorescent proteins. When these fluorescent proteins are illuminated with blue or ultraviolet light, they glow brightly.

Zebrafish as an Ideal Model Organism

Zebrafish were chosen as the organism for creating GloFish because they have a number of advantages for genetic modification:

  • Rapid reproduction – Zebrafish breed frequently and produce large numbers of eggs.
  • Rapid embryonic development – Zebrafish embryos develop quickly, allowing quick screening for transgenic fish.
  • Transparent eggs – Zebrafish eggs are transparent, making it easy to visually screen for fluorescence.
  • Well-studied genetics – The Zebrafish genome has been mapped extensively.
  • Low cost – Zebrafish are relatively inexpensive to obtain and maintain.

These attributes allow large numbers of Zebrafish to be bred and modified efficiently to produce GloFish.

Fluorescent Protein Genes Used

The original GloFish incorporated genes for green fluorescent protein (GFP), harvested from the jellyfish Aequorea victoria. Later generations of GloFish added genes from other marine organisms:

Fluorescent Color Gene Source
Green GFP from jellyfish Aequorea victoria
Red DSRED from coral Discosoma
Orange DSRED2 from coral Discosoma
Purple/Violet Chromoprotein from sea anemone Entacmaea quadricolor
Blue AmajL from jellyfish Aquorea macrodactyla

By mixing and matching genes for different fluorescent proteins, GloFish can be created in a rainbow of glow-in-the-dark colors.

Creating New Varieties of GloFish

Since GloFish are transgenic, they pass their fluorescent traits directly to their offspring. By selective breeding of the fish displaying the brightest colors, scientists can develop new stable lines showing strong fluorescence.

New varieties can also be created by re-engineering the Zebrafish genome. Some ways they develop new strains include:

  • Introducing different combinations of fluorescent proteins to produce new colors.
  • Targeting fluorescence genes to new parts of the body, like the skin or fins.
  • Breeding GloFish with other brightly colored or long-finned Zebrafish varieties.

There are now a multitude of different GloFish strains available, exhibiting an array of fluorescent hues.

Controversies Around GloFish

While popular as pets, GloFish have been met with some controversy over the years. Some of the concerns raised have included:

  • Animal welfare – Does genetic engineering harm the health and wellbeing of the fish?
  • Environmental impact – Could released GloFish interbreed with wild populations and pass on their genes?
  • Regulation – Should genetically modified pets undergo more regulation and safety testing?
  • Ethics – Is it ethical to modify organisms solely for aesthetic purposes?

To date, there have been no reports of GloFish having adverse health effects or being released in significant numbers into natural habitats. However, the debate continues around transgenic pets and how they should be regulated worldwide.

The Future of GloFish

GloFish remain the only genetically modified animal legally allowed to be sold as pets in the United States. They continue to be developed with new fluorescent colors and patterns for the ornamental fish trade.

A few directions that may be coming soon for GloFish include:

  • New species – Scientists could apply genetic engineering to make other species like tetras glow.
  • Custom strains – Hobbyists could use CRISPR gene editing to develop unique GloFish strains.
  • Biomedical research – Their fluorescence makes them useful models for studying diseases.

While controversial, GloFish have carved out a niche as the first commercial genetically modified pet. Their striking colors will likely continue wowing aquarium keepers and sparking discussion about bioengineering in the coming years.


GloFish represent a landmark application of genetic engineering to create a unique ornamental aquarium fish. By inserting genes from jellyfish and corals, scientists activated Zebrafish to fluoresce in a dazzling array of colors. Their development has opened up both opportunities and debates about transgenic pets. While future technical and regulatory challenges remain, GloFish have staked a claim as a popular fluorescent fish on the aquarium market.