Petrale sole fish or Rex sole
I purchased Petrale sole fish at 99 Ranch Market for $1.99 lb. I was surprised usually I pay $7.99 or $9.99 per lb at other markets. I also was told by the seafood clerk at 99 Ranch that Petrale is the same fish as Rex sole. I fried the fish with cornmeal and flour as usual, the fish was mushy and broke apart while cooking, the worst fish I've ever eaten, had to throw away. I'm not sure what I purchased.
I find tilapia every bit as good as petrale, and much cheaper. Somehow, petrale has acquired an undeserved reputation. While not a flatfish,it can be treated as any flounder, etc.
A lot of those flatfish will practically melt if you overcook them even a little, especially if they aren't extremely fresh. The fish that's sold in CA as Dover sole is one "melter" that I've read about, but I've even had a large chunk of halibut turn gooey.
All those little guys like Rex sole and sand dabs (if you can get them!) do best with only a light seasoning and at most a dusting with flour, and then a quick turn in the pan with some butter - and if the butter burns then the pan's too hot. That's a good thing to do with tilapia, too, BTW.
Sole is a very delicate fish and doesn't stand up well to breading or high-heat frying. The only way I will cook sole at home is steamed en papillote (in parchment) w/ a few julienned veggies (leeks, carrots, zucchini), fresh thyme, and EVOO. It's not one of my favorite fishes though...