The only thing that I can think of regarding the legality of Tilapia in Missouri (or other states where they cannot overwinter) is...what if they get into the river system and work their way into areas where they can overwinter. I'm not for or against the idea, but it may be the "thought" of why they are restricted.
Humor has it that a fish farm near the center of our state (very near the Missouri River) flooded out in '93 and that's how the Asian Carp got loose. Apparently, they were pond farming them as a food source (they are good to eat, btw) and the flood waters overtook the pond/s and the rest is history.
