Hmmm...not sure about the "catfish thing"!
But they are very calm and get along great with other fish. I've seen the koi push right through them to get to food and they just tolerate whatever comes their way. I was concerned about the water temps but they've been through two winters now so they're doing well. Many people keep them in aquariums from what I've read.
I've seen a couple 10 inch Hifins and they still had that same shape and hi dorsal fin, but they do lose it when they get older and much larger. I've heard of them getting to be over 30 inches, but in a pond like mine they'd probably not get that big. They are slow growers, too.