When they are as little as you are getting them at stores, you can't tell the sex. They basically all look like girls at one point. Hence why I have a female named Doug!
Sounds like Doug and Dexter would be the best of friends. In the beginning I used to correct people when they called her “he” but now I’m just like screw it, they are never going to remember. We have a female Pac-Man frog named Otis, I even call her he sometimes LOL!