Sounds more stressed than male.....do a couple water changes. They shouldn't be sexable till they are about 10 to 12" for cincta. Not sure if you can sex cincta the same way either. Pikes have an elastic stomach for a reason, they know when to stop eating. I've never had one die on me from over eating, and i feed mine A LOT, there must've been something else...as a side note...check aquabid.com they have pikes for sale a lotta the time....and Miles, as well as John import from Peru....so they should both have cincta.