What's with that dirt flavor?

I love to make fish tacos. My mother showed me how years ago, in her attempt to duplicate the fish tacos at Taqueria del Sol. I usually make them with talapia, but recently I've noticed a funny dirt type flavor in my talapia.
I thought it had to do with the freshness of the fish, but I made sure before I cooked it that there was nothing funny going on. Sure enough, they still tasted like dirt. I did a little on-line research and found that I'm not the only one. http://chowhound.chow.com/topics/375516 It seems that maybe it has to do with the pellet food it has been fed when farmed. Or maybe the dirty water it's been raised in, but regardless, I don't know that I'll ever get talapia again. (Although one post I read seemed to believe that talapia from Trader Joe's is fine. And another suggested that it's the fish raised in Asia that is the worst. If you get it from South America it's much better.) I have made these fish tacos at the beach with really fresh fish like grouper or snapper (can't remember which). So I won't give up on the whole recipe and idea - just the talapia.

Whatever the fish, cut it into strips about 3 inches long. (I usually cut it into four strips lengthwise then in half or thirds.) In a large ziplock bag, I put about a cup of flour and a teaspoon of salt and a bunch of grinds of black pepper. Throw the fish in here and toss it around. Heat a few tablespoons of olive oil in a pan over medium high. (I know it's ready when I splash a few drops of water in there and they sizzle and spit and dance across the oil.) Add the fish and fry until golden brown. Flip over and do the same on the other side. If you have some pieces that are particularly thick, I then put those on their sides to get golden. You can then drain these on a paper towel lined plate. If you're cooking for a crowd and doing batches or you're waiting for someone to get home, you can put the plate in a 200° oven until you're ready to serve.

Mmmmm Sauce:

I grew up on Blue Plate Mayonnaise. It's the only one for me. Sauce is made from Blue Plate, diced pickled jalapenos, and a spoonful or so of the juice from the jar of jalapenos.

Other yummy additions:

sliced avocados

salsa from the Oak Grove Market

Serve on soft flour tortillas warmed on a dry skillet.