She looks like she might be pregnant, or just very well fed. It's pretty common to buy them that way. =) When they're getting ready to go into labor they like to be by themselves, and will sometimes hang low to the ground and just be there. lol They act pretty weird when they go into labor, they will sometimes hit their sides or tail on an object, but mostly they stay still somewhere with their fins down, when they push they look like they're doing a threat display though, and usually all fins stick straight out, so watch for that!
Also, it could just be that they're new. Males tend to be a little more adventurous in a new tank, but can be shy. It's usually the girls that like to hide out when you first get them. In other words, when you just get them, they can be less energetic and shy for the first week or so.
If you have a large cycled, planted tank(Like a 30 gallon), with a lot of hiding places, you should get more girls. Otherwise the male will pester the female all the time, and this could lead to her being severely stressed out, and even cause her death. If you have a tank smaller than a thirty, like a twenty gallon, you should still get at least one more female, if you have a thirty+, you could fit two more girls. =) With mollies it's good to have at least 3-4 females to every single male. It's not recommended to have mollies in anything less than a twenty gallon tank because they not only get big for some types, but they have a very high bio-load and it can hurt the quality of your water if you have too many.
It looks like you have two gorgeous orange sailfin mollies(The male anyways, the female looks like a Creamsicle), and those get to be about 4 inches long or so if I recall correctly. They're commonly confused with Creamsicles though. =p If they are Orange Sailfins, consider yourself lucky to find them! It's not easy. Creamsicles can also have that "Thick" look to them without being fat or pregnant, they're kinda big fish!
Oh, I should also tell you that if you DO choose to get more girls for him, they don't all have to be the same kind of molly. Most molly species get along well, they come in all sorts of shapes, colors and sizes, and they can interbreed. =) Incase you find you like another kind of molly. ^_^ I have a pretty mixed tank myself, but I try to get atleast two of the same type from the same tank, as it sometimes makes it easier when they have a bond. Other times they just don't care so long as they're with other mollies, so keep that in mind.
Last edited by Sylverclaws; 10-21-2012 at 04:19 PM..