Is it pregnant?

About 2 days ago I had gotten 4 leopardfish and 2 fry at a store I go to often. The lady said she had given me males and females and started to explain the difference between the two but obviously I was paying attention as I was looking at apple snails. Anyway, I had gotten home with them but I noticed one the fuller looking one( at the very back) was swimming weirdly and like spinning around but would be fine the next minute then go back to doing the weird swimming. I was wondering what the gender is and if it's pregnant and what does the spinning mean? I could provide other photos or a video of needed! Thanks!