If the scales are sticking out, then it's dropsy. Dropsy could be bacteria or bad water conditions. There is anotehr form where the fish may have swallowed too much air along with the good. Some suggest to soak your food first in water, then use a turkey baster to squirt it into the tank, under the water line.
Otherwise, it could just had overeaten. I had a few zebra danios and they are the quickest swimmers in the tank. Therefore, they get to the food quicker.
Don't feed any of your fish for a day. Fish should actually be fed about 6 days a week. This helps clean up their system. The following day, feed your fish some frozen peas (skinned). This is a natural laxative for the fish.
But first check to see if the scales are sticking out, then treat from there. Otherwise, try the frozen peas.
Oh yeah...It would hurt if you do a 15%-25% water change and light gravel cleaning.