You don't put Parmesan on fish.
par-mi-GIA-no — stress on third syllable. The 'gi' sounds like the 's' in 'measure'.
Know this rule before asking for Parmesan in an Italian restaurant. Asking for Parmesan on a seafood dish or on a carbonara will cause visible discomfort to your waiter. The rule extends to several other dishes.
Italian food rules: no Parmesan on seafood (fish, shellfish), no Parmesan on carbonara (the egg provides richness), no Parmesan on pesto pasta, no Parmesan on dishes with truffles (the flavours clash). These are not suggestions — violating them in front of an Italian marks you as someone who 'doesn't understand food'.
Scusi, posso avere del parmigiano?
Excuse me, may I have some Parmesan?
Always acceptable to ask — good waiters will gently advise if inappropriate.
È normale mettere il parmigiano su questa pasta?
Is it normal to put Parmesan on this pasta?
Asking first shows respect for the cuisine.
In questa regione usano il pecorino invece del parmigiano.
In this region they use Pecorino instead of Parmesan.
Regional variations — Rome uses Pecorino Romano, not Parmigiano Reggiano.
Italian culinary rules are deeply felt and regionally specific. The prohibition on Parmesan with seafood dates to ancient Roman taste distinctions. Breaking these rules in front of a traditional Italian family is equivalent to, say, putting ice in a fine red wine — technically possible but socially damaging.