Let me repeat this: glowfish have been injected with a gene that allows them to have their color. When they are bred, this gene is passed on. To be more precise, all glowfish are related to a glowfish ancestor that was originally injected with the gene and reproduced.
Anyway, unless you desire the glow-in-dark effect, I'd recommend breeding normal zebra danios so you don't have to deal with legal problems if you sell them.