This sounds like pickled fish my mom makes(SE Asian). It's pretty good. I some times use it when cooking scrambled eggs to flavor it. lil bit of oil, lil bit of garlic, lil bit of pickled fish.. sautee, then crack some eggs over it.. yum!!
What's even better is pickled fish eggs.
Interesting, in that pickled fish (herring, usually, not sure if any other fish get pickled?) is common in many continental European countries, at least the northern ones. I presume pickling was invented independently all over the world?
But I think that's different (and sounds way more palatable to me!) to _fermented_ fish. I mean, that's basically rotten fish. The cans start to bulge with the gases produced - which is apparenty a sign that it's "good".
Hmmm...reading about it, it seems then that fermenting could be seen as a sort of 'self-pickling'. Where the bacteria that grows in the foodstuff itself produces the acid, thus inhibiting futher bacterial growth - instead of the acids being added separately at the start so as to stop any bacterial growth. I suppose the idea is the bacteria that runs amok is 'good bacteria', and it prevents the growth of the harmful kind.