You are very right, bowls are death traps for fish. Especially goldfish. He will eventually need at least a twenty gallon tank and a very efficient filter.
Does he look like this? http://katsu2.cside.com/kingyo/ryukin/ryukin11.jpg
If so, he could be a fancy goldfish which means the round belly is natural.
Otherwise it could be that he is overfed or has gas. To avoid this problem feed him a very small amount, and use a turkey baster to expel the flakes into the water. Gulping for food at the surface means they are swallowing a lot of air along with their food.
The other, more unfortunate, possibility is that he has dropsy. This is a bacterial infection that causes the body to swell. Another symptom of dropsy is the "pine cone effect", meaning that the scales of the fish will stick out.
~Goldfish do not get pregnant. Because they are egg-layers they become gravid. The odds of a goldfish breeding in a pet store are minuscule.