The fish, a two-kilogram grouper which had been caught locally earlier that day, had already been placed in a baking tray and was set to be cooked for customers when staff at the restaurant spotted its unusual behaviour.
Restaurant owner Riccardo Braghieri, who runs the Cucù restaurant in Camogli, noticed that the fish was still opening and closing its gills, as if gasping for air. This was despite the fact that it had been out of water for several hours.
Braghieri approached a friend who was dining in the restaurant and was an amateur angler, to ask for advice. The friend agreed that the fish was still alive and offered to return it to its natural habitat.
Restaurant staff christened her Marta, after a hen in an Italian comic book series, who is the subject of repeated kidnapping attempts by a wolf, but is always saved thanks to a sheepdog.
Marta was put into a basin to allow her to breathe normally, before being released safely into the sea at Camogli, near Genoa.
"We are all happy. But without her tenacity and desire to live, it wouldn't have happened," the chef wrote on Facebook, sharing a video of the fish. "Some would call it a miracle."
The video has been viewed almost 2,500 times on the social networking site, and Marta's tale has been covered in some of Italy's largest newspapers, including the Corriere della Sera and La Stampa.
Marta's story comes just a week after the government in neighbouring Switzerland ordered chefs to stun lobsters before boiling them, as part of an overhaul of the country's animal rights law.