You'd think that an army moving through the country would scare up scads of deer along the way, too, but I never heard of it mentioned as a food source, either.
Is it also possible that the streams were not exactly overflowing with scaley edibles? The folks of the time were not known as conservationists and were destroying natural habitats as fast as they could find them - gold mining in particular in N GA likely destroyed the natural ecosystems in that area. The method used at the time was to wash the dirt from the hills and sluice it over mercury into the existing streams - There wouldn't be any fish in those streams today if the Government didn't stock them yearly.