Yes I thought the same thing, but so far things seem to have become more peaceful than usual. As for how I sex them, they have very distinct physical and behavior differences. For starters the females are much more plup than the males are, but the males have much fuller tail fins and a slightly larger head. There is also two large indents on either side of the anal fins of the males. On top of that the females are much more laid back than the males. This lets them swim around more without being chased of by the dominant male. The less dominant male tends to try and front to the dominate male which usually ends in a quick chase.It could cause one to get over zealous... But I hope it doesn't come to that, also how are you so sure they're males?