Freshwater mussels attach to fishes gills in their larval stage as a pasrasite if i remember correctly.I can pretty much guarantee a bunch of freshwater mussels will be ignored,and if your p bass ignore crayfish(most s do) then add some thunderbolt crayfish.
I would think Pbass would nail small crays and bigger ones run the risk of injuring the bass.
I would advocate knifefish, i have never kept knives with bass and have never kept bass, but i find my knives to be very interesting fish indeed, some you should look out for:
-reticulated knife, said to be very busy and eats well, ask K krichardson
-black ghost knives, get large and come from similar areas
-royal, chitala or similar chitala knives. the usual go to for large knifefish