Season the fish. Melt the fat in the grill pan and place the fish skin side uppermost in the pan. Cook for 1 min., then turn with flesh side up and grill steadily until golden brown and cooked, about 5–8 min., depending on thickness of fillets. Remove to a hot serving dish, keep hot. Add the lemon juice to the remaining fat in the pan, reheat and pour over the fish. Sprinkle liberally with chopped parsley.