Yeah perruno catfish are a nocturnal species though with time it should start to come out by day. What have you tried feeding it? It is a rare fish that will turn down live or frozen bloodworms but i notice you have mbuna living with it so that could be a problem, i feed all my large catfish with Hikari sinking carnivor pellets and frozen foods such as fish, mussels and prawns (shrimp).
Do you know the size that catfish will grow to? When full grown it will be pushing 2 feet in length, sorry if you knew this but so many people buy them as "kittens" as they look so cute and dont realise in a couple of years time they will have a huge fish eating monster on their hands.