Fold the pieces of fish into a small bowl and pour in 1/4 cup of beer. Cover the bowl and refrigerate for 1 hour.
Turn on the oven to preheat to 220 degrees.
Sprinkle (or grease) a large baking sheet with vegetable oil. Put the potatoes on an oiled baking sheet in one layer. Drizzle 1 tablespoon of potatoes with unscented vegetable oil. Sprinkle potatoes with 1/4 teaspoon of salt and mix well. Place the baking sheet in a preheated oven and fry the potatoes for 20 minutes, stir once.
Remove the fish from the beer, drain. Sprinkle fillets with 1/4 teaspoon of salt.
In a medium bowl, combine flour, remaining beer, and 1/2 teaspoon of ground black pepper and stir until smooth.
Put the pieces of fish in the batter, mix well. In a large skillet over medium-high heat, heat the remaining 3 tablespoons of unscented oil. Remove the fish from the batter, lightly shake off the dough and put the fillet pieces in a preheated pan, cook for about 3 minutes on each side. Sprinkle fish with 1/4 teaspoon of salt and serve immediately with the fried potatoes.