Marinate the fish fillets with salt, lemon juice, garlic paste, ginger paste and black pepper powder, keep aside for 3-4 hours.
In a bowl, add the flour, rice flour, salt and baking soda, mix well.
Add 3/4 cup of ice-cold water and 3/4 cup of soda water to the flour mix to form a thick batter, add a whipped egg white, sprinkle a little salt. Beat well. Refrigerate for 30 odd minutes.
In a separate mixing bowl, mix the flour, salt and pepper, spread evenly over a plate. Roll the fillets one by one over the flour. Shake off any excess flour from the fillets, dip into the batter.
Heat oil in a deep bottomed frying pan. Lift a fillet from the batter, allow any excess batter to drip off, carefully lower it into the hot oil and fry until golden-brown.