Herring require level 5 cooking and level 10 fishing, using fishing bait and a fishing rod at a bait fishing location. Herring are a grey fish that can be cooked over a fire into a cooked herring, which is pinkish. They can be eaten to recover 5 hitpoints.
A Monty Python and the Holy Grail reference is revealed when a player uses a herring (cooked or uncooked) with any tree. The text says: "This is not the mightiest tree in the forest" There is speculation, however, that the mightiest tree does, in fact, exist. Also, if used with the Grand Tree the text replies "It can't be done!" in reference to King Arthur's response.