Sometimes swim bladder can be caused by deformities. These can be corrected by surgery although its not recommended. It may be there food. There to change there food and feed them pease for about a week. This cure worked on my goldfish so I see no reason why it shouldnt on yours. Boil some frozen/fresh … Read more
Either not much oxygen is getting to the rest of the tank, or the water is too dirtyso there gasping for air at the top.