Dark Herring

The Dark Herring is a fish used as a dagger.

Catching this fish meets the criteria for One That Didn't Get Away.

Source
The Dark Herring can be fished from the inland waters of the Howling Fjord in Northrend, both open water and Fangtooth Herring Schools. It is a rare catch.

Trivia
Possibly a reference to "...cut down the mightiest tree in the forest... with... a herring!" in Monty Python and the Holy Grail.