Maguro bōchō

Long maguro bōchō, used to filet tuna at the Tsukiji fish market

A maguro bōchō in use at the Tsukiji fish market in Tokyo

Main article: Japanese cutlery

Maguro bōchō (マグロ包丁, lit. "tuna knife") or Maguro kiri bōchō (マグロ切り包丁, lit. "tuna cutter") is an extremely long, highly specialized knife used in Japan to fillet tuna and other large fish.

The maguro bōchō is a longer knife with a blade length of 40 cm (16 inches) to 150 cm (60 inches) in addition to a long handle. It can fillet a tuna in a single cut, although usually two people are needed to handle the knife and the tuna. The flexible blade is curved to the shape of the spine to minimize the amount of meat remaining on the tuna carcass.

They are commonly found at wholesale fish markets in Japan, the largest of which is the Tsukiji fish market in Tokyo. They may be found at very large restaurants, but they are not used in a regular Japanese kitchen, unless there is a frequent need to fillet tuna with a weight of 200 kg (440 pounds) or more.

To those unfamiliar with Japanese knives they may be confused with Japanese swords. However, they are not a weapon but a tool, although they have been used as weapons by Yakuza.. 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, as seen in the picture.