A jellyfish gene is injected into the eggs. This does not seem to have much of an impact on the fish's lifespan, however I still don't buy these because IMO it's buying into the commercial nature of glofish. The company has increased the price of a zebra danio 500%, made $30 2 gallon tanks that aren't even suitable for them, and patented the fish, making it illegal to sell offspring that you will almost inevitably get. So in the end I would advise against not buying them, however it is better than dyed or tattooed fish.