Ikejime is a method of cutting off the medulla oblongata (spinal cord) and aorta of a fish, essentially keeping the body alive while killing the fish. The first step is to stab a fish in the head to make it brain-dead. Next, cut the spinal cord in one place and prepare to remove the blood. To drain enough blood, the spinal cord at the base of the tail is also severed. There is also a method of inserting a thin wire, like a piano wire, into the backbone. This technique paralyzes the nerves while at the same time suppressing the putrefied substance that comes from the spinal cord. Finally, soak the fish in seawater to remove the blood.
Using the Ikejime method extends the time until rigor mortis starts, and makes it easier to maintain freshness, while at the same time preventing raw fish odor and damage to the body by inserting a butcher knife into the base of the tail to drain the blood and keep oxidized blood from running throughout the body.