In a large deep skillet heat 1 inch of the vegetable oil to 375F. and in it fry the potatoes, peeled, halved lengthwise, and cut crosswise 1/4 inch thick, in 2 batches for 8 minutes, or until they are golden brown. Transfer the potatoes with a slotted spoon to paper towels to drain and sprinkle them with salt to taste. In a small bowl combine the fish with the milk. Put the seasoned flour in a bowl, remove the fish strips from the milk, letting the excess drip off, and dredge them, a few at a time, in the flour, shaking off the excess. Reheat the vegetable oil to 375F., in it fry the fish in 2 batches for 3 to 5 minutes, or until it is golden brown, and transfer it with a slotted spoon to paper towels to drain. In a large baking dish combine the fish and the potatoes.

In a large skillet cook the garlic in the olive oil over moderate heat, stirring, until it is golden, add the onion, the bell pepper, and the oregano, and cook the mixture over moderately low heat, stirring, for 5 minutes. Add the wine, the vinegar, the sugar, and salt and black pepper to taste, boil the liquid for 2 minutes, and pour the mixture over the fish and potatoes. Chill the mixture, covered, for at least 8 hours or overnight. Let the mixture stand at room temperature for 30 minutes before serving.