A Maguro Bocho, also known as a Maguro Kiri Bocho is an extremely long, highly specialized knife used in Akavir to generally fillet tuna, as well as many other types of large ocean fish.
Often they are used by two people simultaneously, where the second person handles the other end, using a towel wrapped around the blade for protection.
Require smithing skill level 40 to craft - Temperable (sharpening) with a Refined Moonstone
Use cooking pot to convert between 1H and 2H variant, cost 1 raw salmon fillet (there's no tuna in vanilla skyrim, so i choose my favorite fish instead)
Additionally, there's one free to grab at any time on Sky Haven Temple's roof, it's up to you to find a way to get it.