I can personally attest to the fact that they are not sterile. I bought 3 little glofish to go in a little 5-gal, to keep in my little apartment. They were happy for about 2 days until I accidentally killed them (evidently I didn't add enough conditioner to deal with the chloramine). I was going to go back and get replacements at the end of the week, but before I got the chance I noticed a bunch of little glass-like squiggly things at the top of the tank. I have since set up a 12-gal to give me more room to grow out the 80 or so fish I have now. They are definitely fun to watch, especially so many of them together, but they sure are growing. Not quite sure what to do with them all. The neatest part is that about 1/4 of them are albino.