I've had my betta for almost a year, and I've never seen him do this before. Usually he's very active, and he likes to sleep near the bottom of his tank behind a fake plant, so when he started floating near the top of the tank yesterday I started worrying.
He lives in a 2 gallon tank with no filter system, but I change and treat all the water on a weekly basis. He's also got a heater in his tank. He eats a lot, I feed him those betta pellets once or twice a day and he always eats all that I give him (10-15 pellets). He stopped seeming interested in his food about four days ago, but still ate a little.
Since yesterday he's just been floating near the top of his tank, with his mouth at the surface. He is breathing, but doesn't move much. I changed all his water today, but it didn't seem to help. It also looks like the area right under his head is englarged, but he's a large fish already, so it's hard to tell.
Any suggestions/ideas are very appreciated! Thanks!