One of my Zebra Danios began swimming very strangely the other day. It would swim vertically, upside down, and spiral out of control when startled. I took a quick video of what it is doing... https://www.youtube.com/watch?v=akOLNBo4Vgs I did some quick searching which suggests swim bladder disease or tetra disease. I've never had a fish have this problem before, and the other fish in the tank seem to all be fine. Does anyone know what is wrong with this fish? Should I just assume it is dying and put it out of its misery, or is there a way to help it?