After a while you can just kind of spot the sexes of these - the males generally have a more pronounced red and blue stripe color, while the females have a more blue and silver feel to their color overall. The females just "feel" a little more plump and silver to look at when you are looking at a tank of mixed sexes. The males will just look a little thinner and darker red and blue, you just have to be patient and stare at them a while.
~~waterdrop~~