Ikejime: Effectively hit the entire central nerve of the fish's spine

Question

In search for the most humane ways to kill a fish, I have came across the technique Ikejei. This is said to be one of the best methods to preserve the quality and flavour of a fish.

From what I got, the technique consists of more than killing the fish fast. After killing the fish, there's a not so simple procedure for bleeding it by cutting the fish in the gills and in the tail and then, another procedure, of cleaning the blood inside the spine.

Regarding the cuts, I know that in the gills one should cut completely the area that connects the gills and the branchi operculum.

However, one question remains, how to effectively hit the entire central nerve of the fish's spine with a "streak"?

Answer 1

The goal of this technique is to avoid a bad flavor of the meat that comes from certain chemicals released into muscles. Bleeding the fish out is just an additional step.

The key of the technique you described is to destroy the brain and central nerve system down the entire spine, which basically completely stops any "signals" from the brain and exposed nerves to the muscles to contract. This stops the twitching you can sometimes observe after killing a fish. The fish is dead, but the nerves still fire random signals. These muscle contractions use energy, which is created by chemical reactions in muscle fibers, which can turn the meat sour.

To destroy the nerves in the spine, you usually bore a hole into the head of the fish (the tool depends on the size of the fish and the thickness of the "skull", sometimes poking it with the wire is fine) then you use a stiff wire and try to follow the nerve channel into the spine of the fish. Once in there, it is usually easy to push through, as the spine works like a pipe. You can move the wire forwards and backwards to "clean" the spine of any nerves. You goal is to have the muscles stop twitching entirely.