My females get like this for a while, then they spawn and release their eggs. After that, they look normal again for a while. Does the fish's pelvic fin look paddle-shapped, or is it narrow and sort of angular at the end? It seems the females have paddle-shaped pelvic fins. Probably to help deposite the eggs when they spawn? I know I caught one of my albino girls once carrying some eggs cupped in her pelvic fin where she then attatched them to the tank wall. Does this sound right to anyone else?
They say the best way to judge gender is by how broad or narrow they are from a top view... I always went by their pelvic fins. And sure enough, the paddle-shaped ones will get fat, spawn, and then skinny down again while the angular-finned ones just stay about the same (unless they just ate a big meal, of course).