Originally Posted by Taiken5968
It's a female, and it's pregnant.
I can't just leave you with the above answer. Haha
That looks like a type of platty. And it just may be pregnant. Most live breeders are pregnant before they leave the store. The females have an anal fun where as the males have a modified anal fin. That basically means the males have a penis.
Here is a picture of a male guppy, and a drawing of male and female plates.
I hope this helps. And if you need more information let me know.