I recently added an upside down catfish to my aquarium and am really just wondering if he is nocturnal? The first few days he was active during the day, until he discovered his rock. Now he just hangs out (upside-down of course) under there all day. I rarely see him come out, except for maybe 2 or 3 in the morning, a few hours after all the lights in the room have gone out. Is this normal?