I've read several articles and posts on the internet and none of them give definitive way to tell the difference from female molly to female swordtail. I can tell the fish is a molly if it's white or black or balloon shaped or having sailfin, because these features only appear on molly. But for the red females, I can only see that the red mollies are usually a bit more orange than swordtails.
Today I went to a LFS and watched in front of a tank of mollies and a tank of swordtails for ten minutes and still couldn't reliably tell the difference. The shopkeeper wondered what I was looking at so I asked her. But she said those fish are of the same species lol...
Today I went to a LFS and watched in front of a tank of mollies and a tank of swordtails for ten minutes and still couldn't reliably tell the difference. The shopkeeper wondered what I was looking at so I asked her. But she said those fish are of the same species lol...