I had quite a few in my first clutch with those big bellies, I was told it was their yolk sac and it would disappear but now I really don't think it was, mine couldn't swim other than go in circles, they wouldn't eat and I swear the "belly" just kept getting bigger on them, they eventually died. Also there were a couple that developed the issue weeks after being born but most came out of the eggs looking like that. With my other two clutches I'm culling any like that, that I see are not eating or are not moving much because I feel it's much crueller to let them starve to death, some lasted over 30 days looking like that. My second clutch didn't have many of them,