Swim bladder disease, especially common in fancy goldfish, robs fish of their natural buoyancy, and can leave them floating upside down or even stuck at the bottom of the tank.
Swim bladder disease can be caused by high nitrate levels from overfeeding or from internal parasites. It can be cured with a green pea supplement or with surgery to remove the affected part of the swim bladder, but in cases where it can't be cured, why no work around it?
That's just what one ingenious goldfish owner did, as shown in this video:
Ada the goldfish is swimming along just fine in this buoyant harness. Other fish owners have suggested attaching ailing fish to a small block of Styrofoam, which also works.
Ada still has a little trouble eating, but her owner has solved this problem as well, by hand-feeding her.
This goldfish owner has really gone the extra mile to make sure Ada can get around like normal!