Swordfish

You may be looking for Swordfish (Scenes From Her Life).

A swordfish was a type of fish that lived on Earth. The Eighth Doctor once caught one whilst fishing in Vienna. (PROSE: The Sorrows of Vienna)

The Twelfth Doctor stole a stuffed swordfish off the wall of a Sea Devil bar and named it Sonny. (COMIC: Clara Oswald and the School of Death)

In the 40th century, swordfish were among the sea creatures mutated to giant size by an unexploded H-bomb lost off the coast of Spain two thousand years earlier. A group of them attacked some giant sharks, inadvertently saving Pete Nesbit and Hal of the Marine Rescue Brigade. (COMIC: The Sea Monsters)