The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
I hope someone else chimes in for you! I am FAR from expert, but when I tried to sex mine, I learned the males tail forms more of a "v", and the red rays extend out past the end of the tail. Also, the males dorsal fin should extend further back (over the tail) than the females. I would wager that the second pic is a male (as he's identical to mine). Sorry, that's all I can add.
From what I have seen from my own, the females have a nub just in front of the tail along the bottom before the anal fin. On the females it is quite large compared to the males. The picture I have attached is a female.