When To Sex Them?

[JellyPi3]

I currently have a brood of about 30 guppy fry in a tank. Some are about a 4 days older than the others, but the size difference is minimal.

They are roughly about 2 months now, maybe a little less. Some have started to show colour in their tails. But none, as far as i can see, have shown any change in sex. They all started off with a fanned anal fin, and they all still have a fanned anal fin. Does this mean they are all the same sex, or does it develop a little later?

Any help muchly appreciated!

 

[lilfishie]

it will develope a little later on, but generally males get colour first IME, also i have found that a white line appears down the anal fin of potential males, its the gonodium (sp?) forming i think