Ankoro

Ankoro is a gigantic anglerfish under the command of captain Vander Decken IX, residing in the Underworld of the Sea, seven thousands meters underneath the ocean surface. Wadatsumi seems to regard Ankoro as a pet, as apparently Ankoro has needed to be told to "not to eat ships" before.

History
It tried to eat the Straw Hat Pirates and their ship, the Thousand Sunny, but was stopped by Wadatsumi.

Ankoro was later seen again when Vander Decken IX was talking to Wadatsumi about Shirahoshi. As of now, the fish's whereabouts are unknown.

Trivia

 * Its name comes from "ankō" (アンコウ), the Japanese word for anglerfish.