usually when they get to a good size lets say maybe around 3 months is when you can tell the females will be rounder in the belly while males are slimmer and danios I think anywhere btw 6 - 12 months till they are mature enough to mate. which is something unless you rig up you wont see. you have to put them in a small filtered tank that has marbles at the bottom with fake/ or live plants at the bottom and the rest of the space filled with moss leaving only a small portion for them to swim in. this is because they love caviar a little to much. I think they are just so excited and high energy that they just eat the eggs. and when you do get fry they take a while to grow that is why I have the danios in a 30g but I breed them in a 1g or 10g depending on how many eggs I want to go for.