Tokyo Food Safety Information Center » Tokyo Metropolitan Government food safety FAQ » When we eat shellfish dug by ourselves, such as clams for example, what should we pay attention to?

When we eat shellfish dug by ourselves, such as clams for example, what should we pay attention to?

Bivalve shellfish such as short-necked clams may accumulate shellfish poisons if poisonous planktons appear in their habitats. Some conches inherently produce poisons.
Before you go clamming, check whether any shellfish poison is reported in the nearby sea area (For example, search with keywords “name of municipality + shellfish poison”).
Do not catch and eat bivalves from sea areas where occurrence of shellfish poison is unknown and unknown species of shellfish cohabitate.

More information

Type	Major shellfish that reportedly turn poisonous or those that have poisons	Symptoms	Measures that can be taken at household levels
Paralytic shellfish poisons:	Bivalve shellfish such as scallops, short-necked clams, Pacific oysters, and blue mussels.	Symptoms appear approximately 30 minutes after ingestion. Numbing of lips, face, and ends of the four limbs; dizziness, headache, nausea, etc. If the symptoms are severe, the patient may die due to difficulty in breathing.	Before going clamming, check whether any shellfish poisons are reported in the nearby sea area.
Diarrheic shellfish poisons:	Bivalve shellfish such as blue mussels, scallops, short-necked clams, Korean mussels, and bay scallops.	Symptoms appear approximately 30 minutes to four hours after ingestion and can include: diarrhea, nausea, vomiting, stomachache, etc.	Before going clamming, check whether any shellfish poisons are reported in the nearby sea area.
Salivary gland poisons:	Conches* such as many species of whelks, Suruga-bai, ayabora, and Japanese marine mollusk (sold in market as bai or baigai) * Poisonous matters are contained in the shellfish salivary gland.	Symptoms appear approximately 30 to 60 minutes after ingestion and can include: severe headache, dizziness, feeling of seasickness, feeling of drunkenness, staggering, etc. It is reported that the symptoms disappear in several hours in ordinary cases.	At shops or at home, remove salivary glands from whelks with shells purchased in market.
Puffer poisons:	Conches such as whelks, kinshibai, and trumpet shells	Symptoms appear approximately 20 minutes to three hours after ingestion, including: paralysis in lips, limbs, and the whole body. If the symptoms are severe, the patient may die due to difficulty in breathing.	Do not catch and eat unknown species of shellfish.

Some species of shellfish have poisons in the natural condition. The poison-by-poison symptoms and the measures that can be taken at household levels are as described above. To prevent food poisoning from the natural poisons of shellfish, do not catch and eat unknown species of shellfish in principle.