Following up on C'man's post, no amount of raising fish in a hatchery, regardless of their genetic background, can overcome the weakness associated with hatchery rearing. It might help if you think about it in terms of heritable traits instead of the more mysterious concept of genetics. Just like other animals and organisms, fish inherit a lot of traits from their parents. Two of the most important traits are the instincts to forage for food and to seek cover from predators. When wild fish are spawned and their offspring raised in a hatchery, their instinct of foraging for food becomes "softened" because they don't have to search for food. It just magically falls on the water surface several times a day, every day, without fail. The foraging instinct becomes dulled because it goes unused until the fish are realeased as smolts to migrate to the ocean, so they aren't nearly as good at it as their wild counterparts who reared in the natural stream environment.

The second heritable trait or instinct, seeking cover from predators, is dulled even more than the instinct for foraging because their are no predators in the hatchery pond. This is an incredible instinct, because juvenile fish that have never seen a predator, have no idea what a predator is, somehow through inheritance, know that they better find cover to avoid becoming a meal for a predator.

In the natural environment, a juvenile fish constantly has to balance its use of time. Should I forage? If I don't, I won't grow and will starve. Or should I seek cover to avoid predation? If I do, I can't forage and grow, and if I don't, I get eaten and die. Life is constantly in the balance. In the hatchery, a juvenile fish simply eats when food appears, and doesn't have the slightest idea why it flinches when a bird flies overhead or the hatchery worker walks along the pond. Thinking about it, it's a wonder that hatchery fish retain enough key survival instincts for foraging and avoiding predation to ever survive the trip to the ocean and back.

There are other epi-genetic heritable traits that affect survival rates of wild and hatchery fish, but these two outlined above are the most significant ones that come to mind.