From the pic I would say it is a guppy !
Not always. Female guppies are usually fairly short finned, especially when compared to males, and mixing breeds and letting them intermingle can produce weird variations or very boring looking fish. How big is it?
Lol thanks shadoefox. I have many guppies now and I have 1 that looks just like the one in the pics. I just can't stop them breeding now (there like bloody rabbits lol). If you have a male in the tank with her then yes she will be preggers already hehehe !