Platy Sick?

[frog_girl]

Hello, would really appreciate some help with this one!
One of our platys since having her first bunch of fry a few weeks ago, has developed a little patch (5x4mm ish) of what looks like criss-crossing thin black lines or possibly black scarring? at the base of her dorsal fin, head end. Otherwise than that she seems quite healthy, just occasionally at 6-7pm she gets quite quiet and lethargic and spends her time drifting at the top of the tank - very occasionally gasping for air, sometimes drifting down for a bit and then up again.

Everyone else in the tank looks healthy and happy.

We're a bit stumped and a bit terrified that it's something awful and if we don't stop it we're going to have a catastrophe. Any help really appreciated.

 

[taffy1]

any possible of getting a picture? Does it look like she may have been attacked by other fish? Sometimes a pregnant "woman" in the tank is picked on by other fish. If you are concerned about her well being, do you perhaps have a QT tank to move her to? Of course ensure that the water quality is good at all times.