Helping you keep your aquarium beautiful and healthy


My Genetically Altered Fishy Friends

by Robert W. Bly, founder,

Talk about being a sucker for novelty aquarium items: I now have genetically engineered fish in my aquarium.

After seeing them at the fish store for months, I finally gave in and bought 2 of them - "them" being zebra fish genetically altered to glow.

It all started several years ago, when scientists created Alba, a bunny rabbit that glowed in the dark.

Alba was created by French genetic researchers through zygote microinjection. The scientists removed fluorescent protein from a species of jellyfish and modified the gene so that it glowed more brightly.

The modified gene was then inserted into a fertilized rabbit egg cell that grew into Alba. The engineered gene was present in every cell of Alba's body. When Alba rested beneath a black light, the rabbit glowed green.

Now the technique has been used on zebra fish. Zebra fish are so-named because their natural coloring is similar to a zebra's: black stripes on a white body.

The genetically modified zebra fish come in yellow, green, and red. Under normal lighting, they look brightly colored. Under ultra-violet lighting, the fish glow.

My glowing zebras are smaller than other zebra fish I have owned. I assume they will grow to normal size, but only time will tell.

Aside from creating novelty pets, the glowing green gene has legitimate scientific applications. For instance, it can be used to code specific genes or proteins.

When the protein is active, the fluorescence can be detected under a black light. Scientists have used this tracing ability to observe anti-cancer genes by black light, and hope to use the green gene to help locate cancer cells in humans.

Meanwhile, genetic engineers continue to alter the DNA of many species of fish as well as other animals and also plants. The fish are being genetically modified for many different uses.

By genetically engineering fish to grow bigger and faster, we can make fish farming more productive, increasing yields. Geneticists are also working on creating fish that produce prescription drugs such as a blood clotting factor.

In science fiction movies, genetically modified creatures are portrayed as unbalanced, insane monsters that go berserk and wreak havoc. But the genetically engineered zebra fish exhibit perfectly normal behavior: a study published in the Journal of Ethology found that the altered coloration does not affect social or mating behavior in the zebra fish.

Some people worry that dumping of bioengineered fish by hobbyists into ponds and rivers will unbalance the ecosystem. For instance, piranhas that could survive in cold or polluted waterways could be a major problem.

Researchers at the University of California at Berkeley have found a way to make zebra fish glow without genetic engineering. Zebra fish embryos are soaked in artificial sugar, which the embryos use as a carbohydrate building block to replace natural sugar.

Then, through a chemical reaction, a small fluorescent molecule is attached to the artificial sugars. After a few days, the zebra fish embryos glow red or green.

The glow allows scientists to track sugar movement through the cell interior as the zebra fish embryos, which are transparent, develop. Since humans and fish share a significant portion of their DNA, this research contributes to our understanding of human biochemistry.

While the glowing zebra is currently the only genetically modified fish sold in fish stores, there are other mutant fish species that are the result of natural mutation and selective breeding.

One of the oddest-looking fish is the bubble-eye goldfish, a goldfish with huge, fluid-filled sacks under its eyes. This breed was developed in China and is most likely mutated from a celestial or telescope goldfish.

There are other brightly colored fish sold in aquarium stores that have similarly vibrant colors to the glowing zebra fish. These fish, however, are not genetically altered: the colors are added artificially.

If you see a painted cory, the tail looks painted because it was dipped in a dye. Brightly colored Indian Glassfish are injected with a needle under their skin with dye, which usually fades over time.

Avoid buying dyed fish. The treatment can be both painful and harmful to the fish, making them susceptible to illness and early death.

Tropical fish today are available on such a dazzling array of color, you can have a colorful tank without resorting to these dyed or "painted" fish. Hobbyists desiring more brilliant colors than are available with freshwater fish is encouraged to set up a saltwater tank.