Rinse fish with water. Pat dry with a piece of paper towel and season with a small amount of salt and pepper.
In a large bowl, whisk together brown rice flour, oat flour, cornstarch, baking powder, baking soda, a pinch of salt and pepper. Whisk in the seltzer/carbonated water until there are no lumps. Cover with plastic wrap and let sit at room temperature for 30 minutes.
Heat oil over medium-high heat. Dip the fish into the batter, let excess batter drip into the bowl before transferring to hot oil. The batter will be a little soupy, that is ok. Fry until the batter starts to turn golden, about a minute or so depending on the temperature of the oil. Flip fillet so that all sides are fried golden. Place fried fish on a wire rack or plate. Repeat this process with the rest of the fish.
Dip fried fish into the batter, let excess batter drip into the bowl before transferring to hot oil. Place double-fried fish on a wire rack or plate. Repeat for the remaining fish.
This step is optional. You may repeat the previous step if you prefer to have a thicker crust. I find that the double-dip worked really well but I personally preferred the triple dip.
Serve with Traditional Jamaican Escovitch Sauce, tarter sauce or your preferred sauce.