Measure flour into mixing bowl that is large enough to dip fillets in.
Dip moistened fish pieces into flour to coat lightly but evenly. Dust off any excells.
In large mixing bowl whip pancake mix with the club soda to the consistency of buttermilk...pourable but not too thin and not too thick. Beat in the onion powder and seasoned salt.
Dip fillets into batter and drop into hot oil (425° F.) in heavy saucepan or deep fryer, using meat thermometer. Brown about 4 minutes on each side. Arrange on cookie sheet in 325° F. oven until all pieces have been fried.
Serve immediately with tarter sauce.