Glofish are genetically modified fish, GMO fish, what have had genes for fluorescent proteins inserted into their genomes. The genetic change is inherited by subsequent generations. Glofish were invented by scientist who were working on fish that could glow in the presence of environmental toxins. The first step to that end was to develop continuously glowing fish. Naturally occurring genes from jellyfish and corals were used and the results were patented. They were an instant hit with hobbyists who keep fish as pets.