I stumbled upon the wikipedia article about white fish:
Unlike oily fish, white fish contain oils only in their liver, rather than in their gut, and can therefore be gutted as soon as they are caught, on board the ship.
Why of all other properties is the presence of fat in the guts a criterion for gutting a fish aboard or not?
If I didn't read that wikipedia article I would have guessed that the size / amount of the catch and the level of invested and installed automation decides whether the fish is gutted on board or not. Some years ago a fisherman in the north sea told shrimps caught there are shipped frozen to Turkey to be peeled by manual laborers and then shipped back to be sold. I thought the same thing is done with "smaller" fish (maybe sized like a cod and smaller?).