The Old Testament prohibits the consumption of shellfish. Specifically, Leviticus 11:10-12 states:
> But all creatures in the seas or streams that do not have fins and scales—whether among all the swarming things or among all the other living creatures in the water—are detestable to you. They shall remain detestable to you; you must not eat their meat. You must detest their carcasses. Anything living in the water that does not have fins and scales is to be regarded as detestable to you.
Since shellfish, such as shrimp, crab, lobster, oysters, and clams, lack both fins and scales, they are considered "detestable" and forbidden to eat according to this passage.
This dietary law is part of the larger set of kosher laws observed by some Jewish people.