My goldfish has been staying at the top of the tank more than before. I have a air filter and he has been hanging around where the water comes out of the filter and goes back into the tank. I'm wandering if this is normal behavior or if something is wrong with him. I was looking at him and noticed his mouth doesn't open as much as before and when it opens its not as wide as in the past. The area between his mouth and gills looks as thou its pushed in. This isn't new. He has been like this for awhile but he wasn't hanging around the filter and etc. I'm hoping someone can help me out with this issue. Thanks!