Season the fish with a little salt and pepper just before cooking. Heat the frying pan until very hot, then add 2 tbsp oil. Lay the fish fillets in the pan, skin-side down. As soon as it goes in, press each fillet down with your fingers or a fish slice to stop it from curling up. Reduce the heat to medium, then leave the fish to cook for 3-4 mins, undisturbed, until you can see that the flesh has cooked two-thirds of the way up and the skin is crisp and brown. Flip the fillets over, then fry on the flesh side for about 2 mins until just done, basting the skin with the oil in the pan as it cooks. Leave to rest on a warm plate, skin-side up, and baste with the hot oil and juices from the pan.