The usual explanation for why Japanese fish can be eaten raw is that it is very fresh. That answer is wrong in an interesting way, and correcting it explains almost everything else about how fish is handled in Japan.
A fish pulled from the sea and eaten twenty minutes later is at its freshest and close to its worst. It has almost no flavour. The compounds that make fish taste of anything have not formed yet, and the flesh is still contracting. What actually makes fish good raw is a chain of deliberate interventions in the first minutes after the catch, followed by a controlled wait. Freshness is the raw material. The handling is the product.
Ikejime: killing the fish immediately, and why it matters
Ikejime means dispatching a fish instantly rather than letting it die of asphyxiation in a box. A spike is driven into the brain, and the fish is dead in a second.
This is not sentiment. A fish that thrashes for twenty minutes as it suffocates is burning through its energy reserves, and the consequences are chemical and immediate:
- Lactic acid builds up in the muscle, dropping the pH and giving the flesh a sour, metallic edge.
- ATP is consumed. This matters more than anything else, because ATP is what later breaks down into inosinic acid — the compound responsible for most of the savoury depth in fish. A fish that struggles to death has spent the raw material of its own flavour.
- Body temperature rises from the muscular effort, accelerating spoilage before the fish is even on ice.
Two fish from the same net, one spiked and one left to suffocate, are not the same product a day later. On a market floor they will not fetch the same price.
Shinkeijime: the wire down the spine
The second intervention looks stranger. A thin wire is threaded down the spinal canal, destroying the nerve cord along its length.
Even after the brain is destroyed, the spinal cord keeps firing, and those signals keep the muscle twitching and burning ATP. Threading the wire stops that. The measurable effect is on rigor mortis: an untreated fish typically stiffens within roughly four to ten hours, while a fish treated this way can hold off rigor for around twenty-four.
That delay is the whole game. Rigor is what makes flesh tough and what starts the clock on deterioration. Pushing it back by a day means the fish can travel from a boat in Kyushu to a counter in Tokyo and still arrive in the condition a chef wants — and it means the chef has room to age it deliberately rather than racing the fish to the plate.
Chinuki: getting the blood out
The third step is bleeding — cutting the gill arch or the tail artery and letting the fish drain, usually in seawater. Residual blood in the flesh oxidises, and oxidised blood is where most of what people call “fishy smell” comes from. It is also a growth medium for bacteria.
This is why well-handled white fish tastes clean rather than fishy, and why a poorly bled fish smells wrong even when it is genuinely fresh. The smell people associate with fish is largely a handling failure, not a property of fish.
Then the counterintuitive part: waiting
Having gone to considerable trouble to stop the fish deteriorating, the next thing a Japanese kitchen does is let it sit. This is jukusei — aging — and it is the step that most surprises people who assume the goal is speed.
During the wait, enzymes break down the fish’s own ATP into inosinic acid, and proteins begin breaking into free amino acids. Both are savoury compounds. A sea bream eaten the day it was caught is crisp and almost flavourless; the same fish after two or three days under control is softer and tastes distinctly of something. Some chefs take white fish out to a week or more. Tuna is routinely aged.
The control is what makes this aging rather than rotting: constant low temperature, the fish wrapped and the surface kept dry, blood already removed, the flesh never sitting in its own moisture. Which is what the sheet in the next photograph is for.
Those sheets — a permeable film over an absorbent core — pull moisture out of the surface without drying the flesh. They are ordinary equipment in Japanese fish handling and are one of the least glamorous reasons the system works.
Blue-backed fish are the exception
Aozakana — the blue-backed, silver-skinned fish: mackerel, horse mackerel, sardine, saury — do not follow the aging rule. They are oily and enzymatically active, and they degrade fast enough that the traditional handling goes the other way: eat them immediately, or preserve them with salt and vinegar. This is why shime-saba exists as a category at all.
It is also why mackerel is regional in a way tuna is not. A place that eats raw mackerel is almost always a place that lands it.
Farmed is not the poor relation
In much of the world “farmed” reads as second best. For raw fish in Japan the picture is more complicated, and for some species farmed is straightforwardly preferable.
A farmed fish can be harvested to schedule, which means it can be starved for a day or two beforehand so the gut is empty — a significant factor in how fast it spoils. It can be netted without a long fight. It can be spiked, bled and chilled within minutes because the processing is right there. Its fat content is consistent instead of varying with the season. Farmed yellowtail and farmed sea bream are regularly better raw than wild fish that was landed badly.
Wild still wins on peak flavour when everything goes right. It just goes right less often.
The fish that are never eaten raw and fresh
Shirasu — the larvae of sardines and anchovies — are so small that they have essentially no shelf life. Raw whitebait is a genuinely local dish: you can only eat it near where it was landed, and generally only on the day. Everywhere else it is boiled and salted, or dried.
Dried further, the same fish becomes niboshi, one of the backbone stock ingredients of Japanese cooking. This is the other half of the story: not every fish is destined to be eaten raw, and the drying and salting traditions are not a fallback from sashimi but a parallel technology of equal age.
Frozen can be better than fresh
Sweet shrimp are a clean example. They contain an enzyme that starts breaking down their own flesh within hours of death, so shrimp that has never been frozen turns soft and loses its sweetness quickly. Freezing at sea, immediately, stops that enzyme and preserves the texture. The frozen product is the good one.
Shellfish reverse the rule once more. Abalone and turban shells are kept alive until the moment they are prepared, because their texture collapses on death rather than improving. Tanks in restaurants are not decoration.
Freezing and anisakis
There is one more reason frozen fish deserves more respect than it gets. Anisakis, the parasitic larva found in some marine fish, is killed by freezing at minus twenty degrees Celsius for twenty-four hours or more, or by heating to seventy degrees. It is not killed by vinegar, salt, soy sauce or wasabi — the traditional preparations that people assume are protective are not.
So commercially frozen fish is not a compromise on safety; it is a control measure. If you ever get severe stomach pain within a few hours of eating raw fish, that is the presentation to know about, and it is worth seeing a doctor promptly rather than waiting it out — it is resolved by removing the larva, and quickly.
Next: how to eat sashimi — the order, the wasabi, and what is on the plate →
Or: why sushi has seasons →