If you shop at Wal-Mart in Ajijic, look in the frozen fish department for blanco de nilo. It's Vietnamese catfish, no muddy or musky taste, and it's absolutely delicious. Cheap, too. I dust it with flour and sauté it in a mix of olive oil and butter. Mmmm...
If you like catfish, you can buy frozen filets at Costco that are outstanding. Fresh tasting, not fishy, musky, muddy, or anything else negative. We serve them to guests all the time either blackened, breaded and fried, poached, baked with a lemon butter dill sauce, etc. Absolutely delicious.
We also just returned from a month in the US where I ate fried or blackened catfish several times. Not once did the fish have a muddy or musky flavor and that is the difference between something fresh and a fish that is past its prime.