Cetopsis species catfish pretty much have to be kept in a species-only tank, MAYBE with tiny community fish floating over head.
My fiance experimented with them at the LFS where he works -- one of the managers had ordered a few in as a curiosity. AT MINIMUM, they WILL bite and twist off chunks from soft, exposed flesh (he tried out tilapia filet and a one-time experiment with a fancy goldfish from the store's deadpool). The damage to the goldfish was directed at its vital organs, and would have been sufficient to severely injure the fish, which would likely succumb to secondary infections or outright die from repeated bites to the same spot if not caught in time.
One of the customers that one got sold to (when he was not there to mention their feeding habits) came back and tried to return the fish because it had killed two of his oscars, but that is a third-hand account from me.
