Fry Development

Hi!
So out of the 15 or so guppy fry I found a few weeks ago, I have only one left.. T-T
However, I have noticed that the fry has gotten bigger and hadn’t been chased by anybody else in the tank.
I was wondering, since the guppy in the tank is female, around what age can you tell the gender of the fry or it’s type/strain of guppy if at all?
I have noticed some black coloration from the base of the tail up the sides of the fry.
I will post pictures with the fry circled.
Thanks!

You can usually tell the gender when it’s around 2 months by looking at the bottom fin (fan for female, pointy for male) my fry has only just got its base colours at 6 months old and is starting to get some markings.

It’s also best to get a breeder tank for it till it’s big enough not to be eaten by the other fish.

Thank you!
The reason I don’t have a breeder tank is because I’m not able to keep all the fry I get, so I let whatever happens happen, not that I don’t want any fry to survive, I just currently cannot provide for all of them in a separate tank.
Thank you though!

I understand, but if you change your mind you don’t need a separate tank https://www.amazon.co.uk/dp/B073P47WBL/?tag=< that’s the breeder tank I had it just helps separate them, they’re in the same water so no need for an extra filter. I may have worded it wrong by saying tank but I didn’t know how else to put it.