How do hatchery fish impact the native species?
Hatchery fish have not been selected for survival by the environment but by the hatchery. They are often poorly adapted to the particular environment in the long run and many can’t even breed in the new habitat (which is why they have to be reintroduced every year). They are released in such huge numbers however that they can swamp the river or lake they are placed in. Native species have a harder time competing against the larger numbers of fish being added and some end up hybridized or preyed upon as well. This destroys the native species ability to adapt to its native waters and can cause them to become extinct. This can open the habitat to exploitation by invasive species of other sorts as well.
