Rome airport restaurant
It has been years since I last ate there, but I have had decent seafood meals at the restaurants on the north side of the canal that runs through the center of Fiumicino. There are also places in Ostia and Fregene, near the beach. In Fregene, Da Mastino used to be good, though pricy.
There are a couple of options in Fiumicino for good seafood. Try Bastianelli al Molo $$$ or Pascucci $$, while in Fregene the only option is Il SanGiorgio that is actually located in Maccarese. Based on my latest experiences il Mastino has gone downhill and still charges top $$$ unless you're a politician or a TV star.
Hope this helps
I just stayed at the Courtyard last week and ate at a restaurant not 50 feet down the street from the hotel. Don't remember the name, but it was out the door of the Marriott restaurant, turn right and then it's across the street. Excellent seafood and very reasonable prices (about 12 euros for various seafood pasta).