One of the nice things about natural selection is that it works if you give it a chance. Allow only wild-spawned fish to spawn in the wild in the future and you will get stocks adapted to the conditions. If the fish can adapt to the changing conditions. If not, extinction. But the concern about hatchery fish on the grounds is cured two ways. The first is don't put them there on purpose. The second is to overwhelm the few strays with naturally evolved spawners.

Nature is pitiless. If you aren't capable of survival, you die. End of genetic issues.