Shellfish

“Shellfish” is a kitchen word, not a biological one. It covers two groups of animals that are about as closely related to each other as a person is to a beetle, and the labelling rules split them accordingly.

Crustaceans: crab, lobster, shrimp, prawn, crayfish. The US law names this group specifically, as “Crustacean shellfish (e.g., crab, lobster, or shrimp)”, and it is one of the nine.

Molluscs: mussels, clams, oysters, scallops, squid, octopus, snails. These are one of the fourteen European allergens in their own right. They are not among the US nine.

Why that split matters when you shop

A US label is required to declare crustaceans and is not required to declare molluscs as an allergen, though molluscs will still appear in the ingredient list by name.

A European or UK label declares both, each under its own heading.

So a person allergic to mussels reading a US label has a weaker allergen statement to work with than the same person reading the same product’s European version, and has to read the ingredient list rather than the bold text. The reverse of the situation with Sesame, where the US rule is now the stricter one.

Most people allergic to one group tolerate the other, which is why the distinction is worth carrying rather than treating shellfish as a single thing.

Where it appears away from the fish counter

Glucosamine is the one people miss. Much of it is made from crustacean shells, which is why a joint supplement can carry a shellfish declaration and why it is worth reading a supplement label rather than assuming.

Fish sauce, oyster sauce, XO sauce and many Southeast Asian condiments. Surimi, which is fish shaped and flavoured to imitate crab and frequently contains crab extract as well.

Some calcium supplements made from oyster shell.

Chitosan, used as a clarifying agent and in some supplements, is made from crustacean shells.

The kosher and halal angle

Crustaceans and molluscs are not kosher, and the mainstream position in most schools of Islamic jurisprudence treats crustaceans and molluscs differently from fish and from each other.

As everywhere on this site, what we can tell you is what an ingredient is made from. The ruling is your authority’s, and the wider approach is on the page for reading labels when you keep halal or kosher.