Mac Thomason's politics are a little fishy, and now I know why. Look here and learn more about our piscine pals than you might have wanted to.
Perhaps this doesn't call for so much thought, but I'm guessing that this is why fish go belly-up when they die - their gut is below their center of gravity, so if they don't cut loose once in a while they won't be able to keep themselves righted. Likewise the gas might be fore or aft of center, causing the fish to pitch upward or downward if in distress.
I have no word on whether fish can burp or vomit, or what would happen if you fed them an Alka-Seltzer or put them in a tank full of carbonated water. But if the govt wants to cut me a check for a couple hundred thousand bucks I'll be happy to research it all.