I lost my 14 inch plus tigrinus a few months back and I could figure out why. I figured it out now because my 18 inch royal clown knife just died the same way. I started with heavy breathing, lying on his side, and when he would swim it was only in clockwise direction. The tigrinus lasted almost a month, after being isolated, treated for bacterial infections and fungal infections caused by running into things in the tank. The knife only lasted about 2 days. He was isolated from everyone except a female ray who was recovering from breeding. She stuck him with her barb, which was evident by the skin being peeled away from the barb. Same exact behavior but quicker demise. I didn't even think that it could have been the case the the tig, but I admittedly didn't look to see if any of their barbs were exposed. Anyone else have this experience?