1In 4-quart Dutch oven or deep fryer, heat oil (1 1/2 inches) to 350°F. Cut fish into 8 serving pieces. Lightly coat fish with 3 to 4 tablespoons Bisquick mix.
2In medium bowl, mix remaining ingredients except Tartar Sauce with hand beater until smooth. (If batter is too thick, stir in additional beer, 1 tablespoon at a time, until desired consistency.) Dip fish into batter, letting excess drip into bowl.
3Fry batches of fish in oil about 4 minutes, turning once, until golden brown. Remove with slotted spoon; drain on paper towels. Serve hot with Tartar Sauce.