I have heard there are rare occurrences of naturally spawned tiger trout where brook and brown trout spawning overlap. Not sure if that is true or not. Like mules, I suspect an amorous horse and donkey may have gotten together before man intervened...For all intents and purposes any tiger trout you would target were produced in a test tube.
With respect to our "pure strains of trout" I wholeheartedly agree...just wish there were a few more of those around.