According to thoes few published EX fisheries bios who are not genetisists... They can and do on a continual basis tell hatchery fish from wild fish via genetic testing.
they are genetically the same asn you and I are genetically the same. However your genes may make you more resiliant to certain conditions ald less resilliant in others.
For instance a person who is fair skin is not adapted to lots of direct sunlight and may be at more of a risk for certain skin diseases caused by excessive sun. If that person mates with someone who is also fair skinned and that continues to happen throughout the generation you'll develop a race of humans who are increasingly vulnerable to sunlight. They'd still genetically be human and very similar to us but their genetic traits would make them not survive as well in constant direct sun..

That is what has happened to our hatchery stocks. We have unknowingly selected fish that are geneticallt "designed" for life in a hatchery and they do wonderfully there. but as soon as they are turned loose in the river they have a poor survival traits. They when they spawn in the wild their offspring have no choice but to be of the same genetic makeup that does not allow them to survive in the wild..

Hmm i don't know if i explained that well but I tried..