Greg, if I did my "googling" right, damage to the swim bladder can be seen internally just before a largemouth dies from LMBV,, otherwise there are few symtoms. It is the loss of equilibruim that causes death.

Here are some other possibilities:

Proteocephalm ambloplitis, a larva tape worm parasite.
http://www.blackwell-synergy.com/doi/abs/10.1111/j.1095-8649.1989.tb03397.x

Now some of the new manufactured nanomaterials, fullerenes or "buckeyballs" dissolved in water, have been shown to cause brain and liver damage in LMB as well.

http://nanopedia.case.edu/NWPage.php?page=in.mtp13.007

If it's not viral or parasitic infection then I suspect the liver damage could also come from some sort of chemical contamination as well.