I sent e-mail to the TWRA and just got this clarification back from them.

"The Tennessee limit for crappie in all waters that drain into the Mississippi River is 30 per day with no size limit. The exception is for the Mississippi River itself (includes adjacent sloughs, bayous, and all river runs and chutes, that are accessible by boat from the river proper) where the creel limit for crappie is 50 per day with no length limit. "