They were originally just danios, but recently there are skirt tetras also.

They are genetically altered, using squid DNA. One of the colors uses a coral, I think the pink one. They are egg layers, and are born with the color. If they breed, the young carry on the new fancy color. Some colors have a higher rate of return than others. I don't remember the percentages, but I know the green was the lowest so were sometimes out of stock.

The danios are a very hardy species, move quickly, and will school but will not be threatened if they are not kept in large groups. Frankly, they can be a little snotty. Fin nippers, a little bit. The skirt tetras can get large, compared to a danio at least, and have always been docile in my tanks, yet not at all threatened by slightly more aggressive species such as the danios, german rams, breeding livebearers, etc.

I thought it was interesting that the skirt tetras are appearing as glo fish now. The skirts and glass fish used to be subjected to injections, which was cruel and often led to infection and death. The genetically altered glo fish have an excellent survival rate since only the original breeding stock is subject to treatment, and generally hardy species are chosen.

By the way, if you choose to breed them, you can't sell the babies as Glo Fish! They have a patent... ;)