One shark catfish will do nothing other than mope around, except perhaps go periodically frantic if disturbed. Though these catfish are often hyped-up as "deadly predators" it is difficult to overstate just how gentle and sensitive they actually are. Firstly, they like company, and at the very least should be kept in pairs. Trios are better, and schools of dozens best of all! Secondly, they respond to the situation in the aquarium. If kept with peaceful fish, they are outgoing, but keep them with anything aggressive and they panic or try to hide. Made this mistake mixing them with triggerfish. Finally, they are, like all catfish, they have amazingly good hearing (sort of dog-level sensitivity, hearing things we can't). So if the tank is anywhere noisy, e.g., by a door that slams shut, they won't ever settle down.
In short, get your kitten a playmate or two, and check the tank is nice and peaceful.
Cheers, Neale
