Fluorescent Glofish that you see in the
lfs were not harmed at all. No dying, no injections. They are genetically engineered zebra danios. Scientists inserted a piece of DNA containing a jellyfish fluorescent protein gene into a fertilized fish egg. Then, they mated the fluorescent fish to produce a purebred strain. The DNA and the fluorescent protein that it encodes are harmless to the fish.
Interestingly, they originally bred these fish to study and detect freshwater pollutants. In addition to the fluorescent protein gene, they also inserted various DNA regulatory elements (enhancers) that are sensitive to pollutants like heavy metals. When the fish were exposed to water containing tiny amounts of pollutants, the flourescent gene would be turned on and the fish would glow under
UV light.
At my aquarium club aution, somebody was selling some longfinned glofish. So, apparently some clever hobbyist out there has bred glofish with longfinned danios and managed to get a fertile hybrid.