Whats the difference between a feminine swordtail and a womanly platy?

I had bought a pregnant fish today and i know its either a womanly swordtail or a female platy but i wasn't concentrating when i asked for a pregnant fish in the fish shop because i was looking at other fishes but i know its any a female swordtail or platy because i saw the man who served me that he was looking at 2 tanks which be the tanks for swordtails and platys and said this is the nearest one to give birth so i bought that one. But now i get it in my tank i don't know if its any a female swordtail or a female platy. Please help! And my fish mostly stays around the filter. Is this suppose to do this? So my question are:
1) How do you tell a female swordtail to a female platy?
2) Should my pregnant fish stay around the filter?
Answers:    Here is a picture of a feminine platy:
http://www.flickr.com/photos/boardy21/22...

Here is a female swordtail:
http://www.flickr.com/photos/mrander/259...

platys are short and have a more stout body
swordtail females are like longer platies

Your fish may be staying around the filter for a couple of reason. It may be drawn to the water current, as that is usually an nouns higher in dissolved oxygen. Another possibility is that the nouns may be staked out by your fish as its territory.
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