Rinse fish fillets under cold water, cut into 2-inch wide strips; place in a large bowl.
Cover fish with buttermilk and mix with hands; cover and refrigerate: let soak for 30 minutes to an hour before frying.
In a large zip top bag, combine flour, cornmeal, cajun seasoning, garlic powder and black pepper.
Heat oil in a large iron skillet over medium-high heat to about 400 degrees.
Meanwhile drain off buttermilk from the fish. Drop 3 to 4 pieces into the cornmeal mixture and coat each piece well.
Fry fish pieces for 3 to 4 minutes per side, or until golden brown.
Remove from hot oil and drain on paper towels or brown paper bags.
Serve hot with tarter sauce.