In Milan, maybe you can find so many places for seafood, but there are a few restaurant which serve you fresh traditional seafood, one of the famous one which is give you seafood originally from "Sardegna" is " Al Molo 13 ".
You have to book a table for sure! The kind staff will advice you about the Menu and the Drink! I suggest to try the very traditional Wines from Sardegna region.
For food, If you have doubt about your choice, you can easily ask from the staff! They are so patient and so kind and they suggest you all the best choices for you.
Buon appetito !