I have never been fortunate enough to catch one in the wild, but they do ocur naturally; however, they are sterile...
I have not heard of any state dnr, or dept of fish and wildlife actually raising and stocking tigers, though some private organizations do.
I would imagine most of the tigers caught are natural...

a char can spawn with a true trout because they are not that far off... they are a part of the same family (salmonidae)they only differ inthe genus and specific epithet...