Which Fish Are Kosher?

Fish are the simplest of the three categories and the one with the most practical traps.

The signs

A kosher fish has fins and scales. The scales must be the kind that can be removed without tearing the skin — which is the detail that does the work, because many fish have something scale-like that does not qualify.

Every fish with the right kind of scales also has fins, so in practice the scales are the test.

Excluded, therefore: shellfish and all crustaceans and molluscs; and fish such as catfish, eel, shark, monkfish and sturgeon. Sturgeon is the reason most true caviar is not kosher.

No slaughter, and pareve

Two consequences that make fish unlike meat and poultry:

• Fish require no shechitah. There is no slaughter requirement at all, which is why fish products are so much simpler to certify than meat.
• Fish are pareve. They are neither meat nor dairy. Many have the practice of not eating fish together with meat, which is a separate matter of health-related custom rather than the meat-and-dairy prohibition.

The fillet problem

Here is where it becomes practical. A whole fish with its skin on can be checked — you can look at the scales. A skinned fillet cannot. Once skin and scales are gone, one white fillet looks much like another, and you are relying entirely on what you are told.

This is why fish is bought whole, or with a patch of skin left on, or with reliable supervision. It is not a theoretical concern: it is the ordinary situation at a fish counter.

Identifying signs where skin is gone

Where the usual signs are absent, other distinguishing features can serve. Herring is a good example: its flesh carries a natural silvery-blue colour distinctive to that fish and not found in others. Where a skinned herring lacks that colour, it cannot be accepted as herring — the identifying sign has gone, and nothing else establishes what the fish is.

That is the general shape of the answer: what is relied on is a feature that reliably distinguishes this fish from others, not merely a plausible appearance.

Transport and handling

A related question that comes up often: if kosher fish is moved by a non-Jewish driver, is there a concern it was swapped?

The reasoning here is instructive. A non-Jew has no credibility in matters of prohibition — but he is also not suspected of causing a Jew to transgress out of spite. The concern arises where there is something to gain. Where a driver moves fish from a facility handling only that one kosher species, and stands to gain nothing from substituting it, there is no real concern.

What supervision your fish requires, and which species your community accepts, is a question for your rav. See also which birds are kosher.