For the most part, Deadliest Catch is real. Some things were set up for the camera, like the captains talking over a burn barrel. They never did it before yet said it was always done, and it was never filmed nor talked about again. I think that some of the practical jokes were done for the camera. It's not that they don't do the jokes on each other, I just think that the film crew were told that practical jokes occured and they did them to film them.
This isn't to say that what the viewer sees is not manipulated through editing. One of the captains left the show (Blake on the Maverick, I think it was) because of how Discovery filmed something and showed it and it really didn't happen that way.
So, fake in that they set up scenes and act them out? No, not really. Fake in how they edit and show the story? Sometimes, yes.