For the dill tartar sauce: Mix the mayonnaise, pickles, capers, lemon juice, dill and sugar in a bowl. Taste and add salt and pepper to your liking.
For the fried fish: Heat 1 1/2 inches of oil in a deep skillet (I use cast iron) on medium heat until the oil reaches about 375 degrees F.
Clean the fish with cold water and dry just a tad; the fish should be a little wet to help the cornmeal mixture stick to it. Sprinkle a little salt and pepper on the fish. Add the cornmeal and flour to a paper bag. Sprinkle in the Cajun seasoning. Add the fish to the flour mixture and coat each piece evenly. Transfer the breaded fish to a plate or cutting board.
Lay the fish into the oil in batches and fry until they start to float and are golden brown, 3 to 4 minutes. Rest them on a rack to let the extra oil run off. Squeeze a little lemon juice on top. Serve with the tartar sauce.