information:classification, structural:reformatting, information:extraction, structural:summarization
In religion

Religious rites and rituals regarding food also tend to classify the birds of the air and the fish of the sea separately from land-bound mammals. Sea-bound mammals are often treated as fish under religious laws – as in Jewish dietary law, which forbids the eating of cetacean meat, such as whale, dolphin or porpoise, because they are not "fish with fins and scales"; nor, as mammals, do they chew their cud and have cloven hooves, as required by Leviticus 11:9–12. Jewish (kosher) practice treats fish differently from other animal foods. The distinction between fish and "meat" is codified by the Jewish dietary law of kashrut, regarding the mixing of milk and meat, which does not forbid the mixing of milk and fish. Modern Jewish legal practice (halakha) on kashrut classifies the flesh of both mammals and birds as "meat"; fish are considered to be parve, neither meat nor a dairy food. (The preceding portion refers only to the halakha of Ashkenazi Jews; Sephardic Jews do not mix fish with dairy.)

Ichthys has become a symbol of Christianity since ancient times. In the New Testament Luke 24 – Jesus's eating of a fish and Jesus telling his disciples where to catch fish, before cooking it for them to eat. Seasonal religious prohibitions against eating meat do not usually include fish. For example, non-fish meat was forbidden during Lent and on all Fridays of the year in pre- Vatican II Roman Catholicism, but fish was permitted (as were eggs). (See Fasting in Catholicism.) In Eastern Orthodoxy, fish is permitted on some fast days when other meat is forbidden, but stricter fast days also prohibit fish with spines, while permitting invertebrate seafood such as shrimp and oysters, considering them "fish without blood".

Some Buddhists and Hindus (Brahmins of West Bengal, Odisha and Saraswat Brahmins of the Konkan) abjure meat that is not fish. Muslim (halal) practice also treats fish differently from other animal foods, as it can be eaten without requiring the ritualistic slaughter that is prescribed for other halal animals.