Mine just look like they have pot bellies but not really that visible when viewed from the side like in your photos.
Like I said they seem happy. Surprisingly I got 3 of them from Petsmart maybe 6 months ago and all survived. They did go into my 10 gal tank first that had some algae for them to eat and quarantine before moving into my 20 gal. At first they seemed to love eating the zucchini but not so much anymore. And I did put some plants into that tank from my 75 gal that had brown diatoms on them which they really love to eat. It's possible some of the diatoms got on the substrate and that could be what they're eating now.