So I've had my male betta fish for a little over a year now. He has always been healthy, swam around a lot, and always swam right to the food when I fed him. About a week ago I switched him into a bigger sized tank. This tank has a filter and the other one I didn't use the filter just cleaned it a lot. I have the heater going at a good temperature for him and everything.
After I put him in he started acting strange. At first I thought that he was just getting use to the new tank, but a week later he's still not his normal self. He's barely eating anything and he spits his food back out a lot. He just sits on the bottom of the tank a lot and just gets short busts of energy every once in awhile. Sometimes when he's laying on the bottom, he'll lay on his side, which he's never done before. Yesterday was when I started getting really nervous for him, because he went inside this hideaway rock I have for him and laid in there pretty much the entire day. Even when I shook the rock and tried to get him out he wouldn't budge till after awhile. I took the net I use to get him out and brought it right up to him and he just sat there. Before he would swim away, but he was letting me poke him with it even.
As for how he looks, he looks fine. Isn't any paler, can't really see him getting skinnier yet from not eating. He's not bloated, doesn't look like he was a parasites, bacteria or anything like that. He's also blind in his left eye, but that's never bothered him before so I don't see how it would bother him now.