One of my Neon tetras, I noticed the other day, is extremely fat. I've tried and failed to get a photograph, they are simply too fast and my camera just goes all glarey.

She -- I assume it's a she -- has a swollen, round belly. It's not overfeeding as I know what that looks like and this is different. She seems quite aggressive to the others, especially during feeding.

There are no "dull" or white patches on her, which I've learned are NTD symptoms. I think she's been this way for quite a while. She is so fat that her blue line appears very crooked.

Should I be concerned?