It is not unusual to find two wolf fish (Anarhichas lupus) side by side in a hole. I have not found a definitive explanation for this behaviour and can only assume it is related to mating. However, various sources suggest they mate and lay eggs in January but when I see them in pairs it is always during the summer months. It may be they form pairs well in advance of the mating period - or perhaps pair up for life. Certainly these are always mature fish with their full blue colour and one is always bigger than the other. As I look in the hole the smaller one usually edges a little behind the larger. I have never seen sub-adults in pairs.
St. Abbs Marine Reserve, Berwickshire. E. Scotland