Dredge the fish lightly on both sides with flour, salt and pepper.

Heat the oil in a skillet and cook the fish until golden brown on both sides, three to five minutes to a side. Do not overcook. The fish is done when the flesh flakes easily when tested with a fork.

Meanwhile, melt the butter and add lemon juice. Simmer briefly. Transfer the fish to a hot platter, pour the butter over it, and garnish with lemon slices and parsley.