This is how Glofish came about:
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In 1999, Dr. Zhiyuan Gong and his colleagues at the National University of Singapore were working with a gene called green fluorescent protein (GFP), originally extracted from a jellyfish, that naturally produced bright green bioluminescence. They inserted the gene into a zebrafish embryo, allowing it to integrate into the zebrafish's genome, which caused the fish to be brightly fluorescent under both natural white light and ultraviolet light. Their goal was to develop a fish that could detect pollution by selectively fluorescing in the presence of environmental toxins. The development of the always fluorescing fish was the first step in this process. Shortly thereafter, his team developed a line of red fluorescent zebra fish by adding a gene from a sea coral, and yellow fluorescent zebra fish, by adding a variant of the jellyfish gene.
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They are not reproduced in the United States because they came from tropical climate and cannot survive the temperate North American climate.
Source(s):
http://en.wikipedia.org/wiki/GloFish

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Supposedly, some man discovered he could inject the color into a regular danio (zebra fish) from a saltwater fish that glows. I have had several of these fish, and they do not fade in color. There behavior is no different from ordinary zebra fish and they are just as hardy.
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