Hey there! The way to tell the difference between a male and a female is pretty easy. The male has slight pretty blue stripes right behinds its eyes. It also has a small bluish grey spot right near its anus. (the males are usually more colorful) BUT I actually prefer female valentini's as they are a lot less aggressive and less prone to being what we like to call "fin nippers" They're just as cute too! Hope this helps!
Daniel