It is cruel to keep a goldfish in a bowl. Do not even think of buying one. The RSPCA disapproves of them. Bowls are generally not as suitable as tanks, as they do not allow the fish so much straight swimming space. In addition, bowls that curve over at the top reduce the ratio of air-water contact area and thus will reduce the amount of oxygen in the water. The traditional bowl also has no cover so frightened fish may leap out and die for lack of water. Even very large bowls with an inbuilt filter are far from ideal. The tall cylinder or rectangular tanks also have the problem of a small air surface, reducing the amount of oxygen in the water. These, and bowls, look good to humans but are bad for fish.
