I have 4 glo danios (2 blue 2 red). For some reason my red ones are fat as well. I suspect that they just eat all my guppies babies, because when I find guppy fry there are only 2 or 3 in the tank at a time. Also, my red glo danio have been fat for a couple months now and have never given birth. But yours could be pregnant (when it comes to pregnant danios I know nothing). As long as they seem happy and comfortable, I"m not sure that there's much you need to worry about. You could try giving them cooked fresh or frozen peas, which will help them poop, in case they are constipated. If they do seem to be in distress I have heard of fish having some sort of infection that is causing the bloat. By danios have gone through 1 full round of antibiotic treatment with no change (antibiotic was related to another issue) so... they just might be prone to being pudgy.