My Black Molly

Question
My black molly has been staying at the bottom of the tank for a couple of days now and her belly is really big and round she has a light black spot near her anal fin.
so this morning i took her out of the tank and put her in a new one.  
Do you think that she could be pregnant?
should i put her back with the others?
and if she is how long does it take for her the have her fry?
Thanks Rachel

Answer
I think she is pregnant it is very common in Mollies, Black Mollies give birth to 10-60 fry, time between mating and birth, 40-70 days.
She would be better left alone right now, as the other fish might eat her babies, once they are born if she is pregnant you may want to put the mom back in the tank and feed the babies crushed up fish flakes.

Another thing that would be good to do is pick up some Aquarium Salt, not marine salt. and put in the proper dosage of that. Mollies are brackish fish and can be converted over to fully salt water. So they enjoy having some salt in their water.