seems to be confusing as juvies, which is all I have ever seen offered for sale. couple things to look for though.
males usually have a wrinkled pattern behind their eyes. they look like fine blue lines and do resemble wrinkles. they also develop a stripe along their belly although this really comes into play as they mature.
they are also less "round" and more torpedo shaped as they mature.
females-more round and no wrinkles
from all i've read and experienced the best and probably only practical thing to do is get a group and as they mature select the ones you want to keep and sell the rest.
with my tank I have at least 4 mature males. they fight, they swim away, they hide, no real issues because they have a mess of plants and a big enough area nothing gets too serious.
In a small tank I could see real problems occurring. the fighting among the males is not gentle play--they can be pretty viscous.
just my OPINION based on EXPERIENCE. not FACT
when i rescape my tank I will increase their number to at least 20 if not 25. we will see....
thanks for the sexing info
furthermore your experiences "are" based on facts!
they just aren't universally know