Can a platy fish mate with a molly?
No, they cannot. The mollie is a brackish (halfway between sea water and fresh water) water fish and the platy is a freshwater fish. Male platys are usually oversexed (like male guppies) and will try but nothing will come of it. Most livebearers will give birth up to 4-5 times without a male present if they have been inseminated once.