What should I watch for when eating sashimi at home? How do I avoid Anisakis?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Buying mackerel or horse mackerel at the supermarket and filleting it at home for sashimi is a common sight in Japan. But food poisoning from Anisakis, a parasitic worm, ranks among the top reported causes, and actual cases are estimated at more than ten times the reported figure. Here we set out how to handle sashimi at home and how to prevent Anisakis reliably.
Anisakis basics
| Item | Details |
|---|---|
| What it is | The larva of Anisakis, a nematode (roundworm). 2–3 cm long, 0.5–1 mm wide, white or translucent and thread-like. Sometimes coiled and embedded in the flesh |
| Fish it is common in | Mackerel, horse mackerel, sardines, Pacific saury, bonito, salmon, squid, flounder (hirame), yellowtail (buri) and others. Common in wild fish, rare in farmed fish (controlled feed) |
| Where it lives | Mainly in the guts. After the fish dies it moves from the guts into the flesh (muscle). The longer the time, the more likely it has moved into the flesh |
| Symptoms | Severe stomach pain, nausea and vomiting 2–8 hours after eating (stomach), or lower abdominal pain ten-odd hours to several days later (intestine). Also allergic reactions (hives; rarely anaphylaxis) |
| Medical response | In gastric anisakiasis, removing the worm by endoscope brings rapid relief. In the intestinal form, symptoms are managed as they arise |
| Reported cases | 432 in 2023 (food-poisoning statistics; the highest of any causative agent, bacteria and viruses included). Research estimates, however, put actual cases at more than 7,000 a year |
What works and what does not
| Method | Effect |
|---|---|
| Freezing at −20°C for at least 24 hours | Effective. Most home freezers are set to −18°C, so aim for 48 hours or more |
| Heating to 70°C or above, or 60°C for 1 minute | Effective |
| Picking worms out by eye | Effective but not complete. Worms hidden inside the flesh are missed. Check in good light, slicing thinly |
| Removing the guts early, keeping the fish fresh | Reduces migration into the flesh. Gut fish on the boat, or straight after buying, and keep them cold |
| Vinegar, soy sauce, wasabi, salt, lemon | Do not work. Many cases come from shime-saba (vinegar-marinated mackerel) |
| Chewing well | A worm dies if it is damaged, but this is not reliable. Cutting into fine strips (as in ika-sōmen) has some effect in cutting the worm |
Handling sashimi at home: the basics
1. Buy fish labelled "for raw consumption" or "for sashimi". Do not make sashimi from mackerel or horse mackerel sold for cooking. 2. Buy fish last, carry it home with ice packs in a cool bag, and refrigerate at once (4°C or below). 3. Eat it the same day. The use-by date on sashimi is normally the same day or the next. 4. Utensils: wash the board and knife with detergent before and after use, then pour boiling water over them. Do not use the same utensils as for raw meat. 5. Wash your hands, and eat soon after plating. Anything left at room temperature for 2 hours or more goes into a cooked dish instead. 6. If you fillet the fish yourself: remove the guts first and inspect the belly side (the flesh nearest the guts) carefully. Worms glow under a blacklight (UV lamp), which anglers use to check for them. 7. People at higher risk (pregnant women, older people, small children, people with weakened immunity) are safer avoiding raw fish. There are other seafood poisonings besides Anisakis, such as Vibrio parahaemolyticus (summer seafood).
[Verify] The food-poisoning statistic (432 cases in 2023) is the MHLW confirmed figure; the estimate (more than 7,000 a year) is based on a report by the National Institute of Infectious Diseases. Check both against the original documents.
Misunderstanding 1｜Shime-saba or vinegar-marinated fish is safe
Vinegar does not kill Anisakis. Many cases come from shime-saba; it needs fish frozen for raw consumption, or freezing at −20°C for 24 hours.
Misunderstanding 2｜Plenty of wasabi and soy sauce will kill it
They do not work. This is not a parasite that condiments kill.
Misunderstanding 3｜Fresh fish has no Anisakis
Even fresh fish has it in the guts. Freshness only means less has migrated into the flesh; the flesh near the guts still needs checking.
Misunderstanding 4｜Checking by eye and removing worms prevents it completely
Worms hidden inside the flesh are missed. Visual checking is a back-up. What is reliable is freezing or heating.
Misunderstanding 5｜If I get stomach pain, I can wait and see with an antacid
Gastric anisakiasis settles quickly once the worm is removed by endoscope. Severe stomach pain a few hours after eating sashimi: see a doctor promptly and tell them what you ate.
---
Sources
- Ministry of Health, Labour and Welfare, "Let's prevent food poisoning from Anisakis" [アニサキスによる食中毒を予防しましょう]
https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/0000042953.html
- Ministry of Health, Labour and Welfare, "Food poisoning statistics" [食中毒統計資料] (incidence by causative agent, 2023)
https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/kenkou_iryou/shokuhin/syokuchu/04.html
- National Institute of Infectious Diseases, IASR, "Trends in anisakiasis" [アニサキス症の発生動向]
https://www.niid.go.jp/niid/ja/iasr.html
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
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