Ok, ill explain it to you. Ive kept livebearers for about 5 years or so.
When a gravid spot (the black spot near the rear) of the fish becomes very dark and the fish itself grows plump and squarish, her pregnancy is near. If its very dark as you explained, expect fry in about 2 weeks or so. She may abort her pregnancy if you stress her or other fish in the tank stress her. Dont move her into a breeder net or another tank as this will make her abort her pregnancy. If you want the babies to survive you
Must have floating plants on the top of the water so the fry can hide in them, preferablly a plant that other fish cannot get to, Java moss is a good plant or any cluster of plants would work. When she gives birth, purchase a Breeder Net at your local fish store....
Breeder Net (hang on the inside of your tank):
When you have the breeder net, carefully capture the fry and place them in the net. Feed them very finley crushed flakes and preferbly newly hatched baby brine shrimp(optional). Varying their diet is a must for them to grow up properly.
If you dont want to keep large numbers of fry, simply leave them in the tank and they will grow up themselves (a few will survive). Or capture them as said above and take them to your local fish store or give them away.
The Best of Luck,
Tom
