Ike-shime, Neuro-shime and How Our Fish Reaches Us

Nojime, neuro-shime, the Tsumoto method of thorough bloodletting. When a sushi counter speaks about buying fish, these three come before the name of any fishing ground. What is done in the hours or days between a fish’s last moment and its arrival at the shop turns the same fish from the same sea into something else. This article follows that sequence in order, then looks at what has changed by the time a piece reaches your mouth.

Whose hands the fish passes through

At Tanji the fish comes to us directly from the artisans who practise the Tsumoto method of thorough bloodletting: the practitioner who devised it, along with a small number of others who have mastered it to a high standard. Fish dispatched and bled by those hands travel from the coast to the counter.

A short route is itself part of the work. How many hands a fish has passed through, how long it spent in transit, shows plainly in the flesh. When it comes from someone whose timing, whose place, whose method we know, our own decisions about what to do next can be that much finer.

1. DispatchingNojime then neuro-shime, carried out the moment the fish is landed.
2. PreparingBlood drawn out under water pressure, with gills and viscera removed.
3. SendingWrapped under vacuum, sent direct under refrigeration rather than frozen.
4. RestingAged at the shop, the moment judged species by species.

What nojime and neuro-shime bring to a stop

Nojime, a single spike to the brain, is the first move of ike-shime (the practice of ending a live fish cleanly). It kills the fish at once and spares it the struggle that drains its strength. A fish packed into ice while still alive thrashes as it suffers; its temperature rises and lactic acid gathers in the flesh. Cloudy flesh with a slack texture is often decided at this stage.

Neuro-shime follows. A fine wire is passed along the spine to destroy the nerve and the onset of rigor mortis is delayed. The longer that delay runs, the softer the fish is when it leaves the port. What gives rise to umami is not spent on thrashing or stiffening: it stays where it is.

What the thorough bloodletting actually does

The Tsumoto method opens a cut towards the tail and drives water into the blood vessels under pressure. Even once the heart has stopped, pressure reaches the finest capillaries. It pushes out the dark blood line along the backbone as well as blood held deeper within the flesh.

Blood is the main source of a fishy smell. It oxidises as time passes and turns into odour. Where no blood remains, the hours before any smell rises stretch out, so the number of days the fish can be rested tends to grow with them. Bloodletting keeps a fish fresh while also making ageing possible.

Sealed under vacuum, sent chilled

Gills and viscera spoil faster than the rest of a fish. They carry digestive enzymes as well as bacteria, whose influence spreads into the flesh if they are left in place. Taking them out on the spot, once the fish has been dispatched and bled, removes the starting point of decay itself.

From there the fish is wrapped under vacuum and sent chilled. The vacuum keeps oxygen at bay along with drying. It is not frozen because ice crystals rupture the cells between freezing and thawing, letting the moisture that holds the umami run away with them. By the time the box is opened most of the preparation is done, which leaves us free to spend our attention on the resting time and on the measure of salt or vinegar.

Why a fish cleared of blood can rest longer

Ageing is the fish’s own enzymes breaking down its flesh a little at a time. As that proceeds, inosinic acid together with free amino acids, the substances behind umami, increase. The same hours are also hours in which odour develops. Where blood or viscera remain, the smell arrives ahead of the umami.

One reason the Tsumoto method has spread so widely is that it changed how this time can be used. When the number of days available opens up, the right moment can be chosen for each species: white-fleshed fish once their firmness has eased, hikarimono (silver-skinned fish) after only a short rest. Onto those judgements the Edomae repertoire is layered, the curing, the marinades, the nikiri (a glaze of reduced soy brushed over each piece). The thinking behind the work at this Oku-Akasaka counter rests in the same place, classical Edomae technique laid over ageing.

Why tuna and sea urchin come by another route

This process suits fish whose character grows when they are dispatched and bled: white-fleshed fish, silver-skinned fish, the blue-backed ones. Tuna and sea urchin arrive by a different route.

A tuna is one large body, broken down at the port or at the market, reaching the shop through the eye of an intermediate wholesaler. The scale of the handling is simply different, for bleeding as much as for chilling. Sea urchin is the part held within the shell, so there is no dispatching to speak of. It comes packed into its box where it was gathered, chosen on the colour of the grains, their scent, the way they hold their shape. The same word, sourcing, asks us to look at quite different things.

Where it shows at the counter in July

In Tokyo in July the white-fleshed fish firm up: makogarei (marbled sole) and suzuki (sea bass). Fat comes on in aji (horse mackerel) as well as shima-aji (striped jack). Later in the month shinko (the youngest gizzard shad) begins to appear at market. Summer is also the season in which fish turn quickly, so it is when careful dispatching and bloodletting tell most plainly.

The difference stays with you after you swallow. Once the sweetness has come out under the teeth, what remains in the mouth is either umami or the smell of blood. There is no need to decide in a hurry. By the second or third piece, most people notice it as a clarity in the finish.

Frequently asked questions

Reviewed by

Tatsuo Takada

Head chef and owner of Sushi Tanji. Trained in the Edomae tradition and rooted in Kyushu, he leads the eight-seat omakase counter in Oku-Akasaka, Tokyo, and reviews The Tokyo Sushi Guide.