platy sex change?

[Wired76]

I have a gold platy that I got two months ago when she was fairly small. She had a black fan-shaped anal fin, so I figured she was a female. (See the "before" photo!) She's gotten bigger over the last few months, and last night I noticed the black fin is gone and it's been replaced with a longer, gold fin. It doesn't look exactly like a gonopodium; it's almost like she's clenching shut a gold fan-shaped fin. As you can see from the cloudy tank, I had some problems with a sponge filter I installed around my HOB filter's intake tube last night, so she could be stressed. I read that it's possible she was very young when I got her and "bloomed late" into a male fish. Any thoughts? I tried to get the best "after" picture I could, but they were moving around a lot. (In the before photo, she's the one in the upper left, with the obvious black fan-shaped fin.)

 

[coralbandit]

Late male.
Very common with platies and swords.
It is a defense mechanism to help the smaller male survive while it can not get away from Alpha male. Alphas are know to excrete hormones that suppress and dictate the growth of other ,another weird survival technique.
The late male could still turn out to be a better breeder as it always possible with all the Asian stock that the alpha male was influenced by hormonees introduced by the farms in feed which the smaller fish have less access to just be shear hierarchy ...

 

[Wired76]

Yeah, the more I look at him, the more I'm sure he's a him! He doesn't seem to be badgering the other female in the tank, but it looks like I'm getting more female platys now!