Not sure what went wrong, but I don't wash fish before cooking (perhaps that may be my mistake, not yours-), I put seasonings in the flour/cornmeal, not onto the fish before dredging (not that it could make difference-), and I have never fried fish in butter. Butter burns at a fairly low temperature and IMO is unsuitable for frying excpet for eggs, which cook very quickly. I have gently cooked thin sole fillets in butter, but not hot enough to call it frying, and they didn't have a flour or batter coating. I seldom fry fish these days (maybe once a year each for flounder and shrimp) and use coconut, walnut or sunflower oil since I stopped using canola oil maybe a year or two ago. Also, if the fish was less than fresh it might've been sort of mushy--but then, wouldn't it taste off?

I know my method works with frozen fish as well, which I thaw first in the fridge.