Italians never use Parmesan on fish pasta dishes. Our three favourites are tuna in olive oil, roughly broken up, with garlic, capers and creme fraiche (or cream, but we like the tang), sprinkled with chopped fresh parsley; salmon arrabbiata (plenty of home-made tomato sauce with garlic, parsley and a goodly dose of chilli, with rigatoni); and prawns with spaghetti, lemon, garlic, chilli, sundried tomato paste and rocket.   We never use Parmesan on puttanesca either. Just a sprinkling of fresh parsley.