Wally has been with me almost two years. In the last week, he's become lethargic and over the weekend spent most of his time lying on the floor of his tank. His breathing is labored. I've gone through the list of diseases and he doesn't have any of the symptoms of any of them. No lesions, no growths, no change in his fins or color. I did a 100 percent water change on Sunday as I do every week. Yesterday and today, he's been vertical in the water with his head at the surface and making lots of bubbles, breathing more air than water. I don't believe he's eaten in three days. His water temp is 78-80F and his regular food is pellets. He has a 2.5 gallon tank with no tankmates and no filter. I have two others in exactly the same conditions and they're both fine, but they're not as old as he is. Of them, I have had Marty about 9 months and Pete about six.
When I did the water change on Sunday and took him out of the tank, I put him in a cup as I always do while I clean, and he seemed normal while I was doing that.
Any suggestions? Is he just reaching the end of his life expectancy? Can I do anything to help him?