Wash fillets and cut into serving-size pieces.
Lay in a single layer in a large flat dish.
Sprinkle with salt.
Pour in enough buttermilk to cover fillets.
Let stand 30 minutes.
Lift out fillets and drain.
Put oil and butter in large heavy skillet and heat well (there should be about 1/8 inch of fat in pan, so add more if necessary).
Combine flour and paprika in a flat dish and dip fish in mixture to coat both sides lightly.
Drop into hot fat and fry quickly until golden.