What a bummer. I have this little fantail for years. Was perfectly healthy and happy last night. I wonder if the water got too warm and maybe low on oxygen. Had him in my 100 gal stock tank with a buddy. I feel terrible if it was due to my neglect. Maybe should of added more air. We have been having temps in the 90s for the past week. Only other thought was a big frog that has been visiting that tank. Tried to swallow him but maybe he was too big. Not a mark on him though.