Chris, that's really a good question. I feel there is quite a difference in the fight a winter nate puts out compared to a winter hatch. I have no comparison for summer time fish on the coast.
Also, I have spent some time watching fish go through the fish passage facilities at a local dam (lower granite dam) and there really does seem to be a diffreence in the fish. Wild fish look stockier,(which I think makes them look stronger to me) and their fins are usually shaped perfectly. They just plain look healthier.
Hatchery fish, in comparison often have rounded fins and look like they're just worn out by the time they reach this dam. I also notice more "defects" in hatchery fish, such as a crooked tail.
Another problem with hatchery fish in these parts is that they do not reproduce well in the wild if at all. If they did we probably would not be having the problems we are having now.
So, are the hatchery fish different? Well, I'm still not sure. They look different, fight different reproduce different but are they really "genetically" different? I don't know.
Here's a theory I've been tossing around. I think that the environment that the hatchery fish grow in when they are young has a large impact on their developement. Wild fish grow up in an envroinment where they have to work for their food, hatchery fish mill around in a pond for the first part of their life picking up handouts. Just like the kid who grew up working on a farm verses the kid who grew up watching TV making trips to the fridge. Which one do you think will be more healthy in their adult life?
I had the opporitunity to go to a seminar last winter here at Washington state U. about some of the new hatchery practices that some people are researching. I found it extremely interesting that they are now trying to go away from the traditional "pond like" atmosphere and they are now trying to make the hatcheries more "riverlike". The speaker (sorry I forget his name) was running hatcheries that had fish runs with rocky bottoms and obstructions such as brush and logs in the run just like a natural river with natural streamflows. Also, they were experimenting with lower fish densities. They even went as far as adding predators such as a caged merganser so that the fish may learn predator evasion. Even fed the fish from subsurface to keep them lower in the water (more natural feeding style and may help predator impact). The research is not complete so he didn't have a final assesment as to whether this is the hatchery of the future but I think it may be on the right track.

So what does everybody else think? is it really a genetic difference...

Oh Just found the guys name, who was working on this research, Robert Iwamoto, from the Northwest Fisheries Center.

Sorry this is so long, I kinda got carried away.

Duke