My fish has been acting depressed the past few days. Seems sort of "saggy" in the water, less active than normal, tends to go sleep in his tree more than I think he should.
I thought he might be sick but his appetite is ok. He is in a split tank and the other fish is perfectly well.
Yesterday I placed a piece of dark paper over the back of the tank. The back of the tank is nearby a kitchen counter light. The paper blocked the light. I came down this morning and saw that he has right away made a bubble nest (he never made them before) and seems more alert, active and happy. He's been good all day.
Is this a reaction to the light? Can a fish dislike light?