Arkaneo is a giant sailfish that occasionally spawns as a random event at the Deep Sea Fishing hub. She swims around for approximately 50 seconds and grants all fishing boosts after departing. The boosts last for 15 minutes if the player was on the same world when she arrived, or for 5 minutes if the player hopped worlds.
Her appearance and departure prompt the following messages respectively:
The sailfish, Arkaneo, has appeared!
The sailfish, Arkaneo, has departed...
The back portion of her dorsal fin has been removed from her, and attached to Tavia's fishing rod by Tavia during a catching attempt.