Why would goldfish stay at the top of their bowl?

A reason for goldfish swimming to the top is the lack of oxygen. Even if the water is perfectly clean, if you put too many fish in a small amount of water, there may be not enough oxygen in the water for the fish, so they go up to the surface where there is more oxygen. Constipation can be a reason for this weird behaviour too, and I feed my fish the insides of boiled frozen peas when this happens. It actually works! My fish are doing it again, so i plan to feed them the peas today.