I have a roughly 3 or 4 inch common pleco in with my 3-4 inch red bellies and he usually lives in the snake skull type decor I have in there, he only seems to come out when I am out of the room, because when i walk into view of the tank i see him retreat into his skull cave. Also he comes out as soon as i turn my lights off and scurries back when they go back on. Are common plecos usually this shy?