The Tennessee River Aquarium is fabulous! They focus on the river, and while you expect it to be trout, trout, catfish, trout (making me very hungry) it is far more interesting. Many kinds of trout and catfish, but more turtles and the fish are more varied than I anticipated.
The last time I was there, they had an exhibition of jellyfish, too. If I recall correctly, they partnered with the National Aquarium in Baltimore on the seahorse show that just closed. Breeding seahorses was an intergral part of that effort.