Under mainstream Orthodox practice, no. Adult swordfish lack qualifying scales. The Orthodox Union rules it non-kosher. A small number of Sephardic authorities take a different view, but this is not the prevailing position.

What Makes a Fish Kosher? Fins, Scales, and Jewish Law Explained

Q: Do fish need to be slaughtered like other kosher meat?

No. Fish are exempt from the shechita (ritual slaughter) requirement that applies to mammals and birds. The Talmud (Chullin 27b) derives this exemption from the same Leviticus passage that defines kosher fish by fins and scales alone. A kosher fish remains kosher regardless of how it died.

If you’ve ever stood at the fish counter wondering whether a particular species is acceptable under Jewish dietary law, you’re not alone. The rules governing kosher fish are rooted in Torah law and have been clarified by rabbinic authorities for centuries. Understanding the core requirements makes it straightforward to identify kosher fish — and to understand why some popular species don’t qualify.

For a comprehensive overview of all kosher fish topics, visit The Complete Guide to Kosher Fish.

The Torah Source: Leviticus 11:9–12

The requirements for kosher fish come directly from the Torah. Leviticus 11:9–12 states that any creature living in the water is kosher if it has both fins and scales. Creatures in the water that lack fins and scales are considered non-kosher and may not be eaten. This dual requirement — fins AND scales — is the foundational rule that governs all kosher fish determinations.

Deuteronomy 14:9–10 repeats this same rule, reinforcing its status as a core principle of kosher dietary law rather than a later rabbinic addition. Both passages use the Hebrew terms snapir (fin) and kaskeset (scale), and both place the requirement plainly: a sea creature must have both to be permitted as food.

This is the entire biblical test for fish. Unlike land animals — which require ritual slaughter (shechita) by a trained shochet — fish do not need to be slaughtered in any particular way. The kosher status of a fish is determined entirely by species. If the species has fins and scales, the fish is kosher; how it died is not part of the halachic question.

What Counts as Acceptable Scales?

Not all scales qualify under halacha. According to the Orthodox Union (OU), the scales must be the type that can be removed from the fish’s body without tearing the skin. Embedded scale-like structures that are part of the fish’s skin, such as the placoid scales found on sharks, do not qualify.

The Talmud (Chullin 66a–66b) and Niddah 51b specify that qualifying scales are described as kaskeset — scales that can be peeled off. Rashi, the foundational medieval commentator, clarifies that kaskeset means a thin, plate-like covering attached to the body in a way that allows removal. Maimonides codifies the same rule in Mishneh Torah, Forbidden Foods 1:24: a kosher fish is one whose scales can be detached from the skin by hand or with a tool, without damaging the underlying flesh.

Fins Alone Are Not Enough

Every fish with scales also has fins, but the reverse is not true. Catfish have fins but lack the detachable scales required by Jewish law. According to the OU and other major kosher certification agencies, catfish is not kosher. Scales are the decisive qualifier — if a fish has the right kind of scales, it will also have fins. That’s why in practice, kosher fish identification reduces to a single question: does this fish have removable scales?

The Four Types of Fish Scales (and Which Qualify)

Marine biology recognizes four general scale types. Knowing the difference helps explain why some fish are kosher while others — even species that look superficially scaly — are not.

Cycloid scales — KOSHER. Smooth, rounded scales with concentric growth rings. Found on salmon, trout, carp, and most “soft-rayed” fish. These are the textbook example of detachable scales.
Ctenoid scales — KOSHER. Similar to cycloid but with tiny comb-like projections on the rear edge. Found on perch, bass, snapper, tilapia, and most “spiny-rayed” fish. Also detachable; halachically equivalent to cycloid.
Placoid scales — NOT KOSHER. Tooth-like structures embedded in the skin, made of the same material as teeth (dentine + enamel). Found on sharks, rays, and skates. These are not removable without tearing the skin; the OU and all major Orthodox authorities rule these fish non-kosher.
Ganoid scales — NOT KOSHER (mainstream Ashkenazi). Hard, diamond-shaped, non-overlapping bony plates. Found on sturgeon, gar, and paddlefish. The OU, Star-K, and CRC rule sturgeon non-kosher on this basis. A minority Conservative and historical position permitted sturgeon, but Orthodox practice today does not.

Common Kosher Fish Species

The following fish are widely accepted as kosher by the OU, Star-K, and CRC:

Salmon — easily identifiable scales; widely available
Tuna — has small, detachable scales
Halibut — kosher; popular for its mild flavor
Flounder — kosher flatfish with qualifying scales
Cod — classic kosher fish
Tilapia — kosher; scales are easily visible
Trout — kosher; includes rainbow trout and other varieties
Bass — kosher; includes striped and sea bass
Carp — kosher; traditional basis of gefilte fish
Herring — kosher; a staple of Ashkenazi Jewish cuisine
Mackerel — kosher; has detachable scales
Snapper — kosher; red snapper is a common variety

For an exhaustive species-by-species reference covering more than 290 fish, see the complete kosher fish list.

Non-Kosher Fish Species

Shark — embedded placoid scales; does not meet the detachable scale requirement
Catfish — has fins but no qualifying scales
Eel — lacks both qualifying fins and scales
Monkfish — no scales
Sturgeon — controversial; Orthodox say no
Swordfish — controversial; Orthodox say no

The Swordfish and Sturgeon Controversies

Swordfish has scales as a juvenile but loses most of them at adulthood. The OU and most Ashkenazi authorities rule swordfish is not kosher. Some Sephardic rabbinical authorities — most notably the position historically associated with the Aleppo community — permitted it based on the juvenile scale presence, but this is a minority position not followed by the major American kosher agencies.

Sturgeon’s ganoid scales (hard, bony, non-overlapping plates) do not meet the standard halachic definition of detachable scales according to the OU, Star-K, and CRC. The Conservative movement’s Committee on Jewish Law and Standards permitted sturgeon in a 1969 responsum, which is why it appears in some Conservative settings. For those following mainstream Orthodox practice, both swordfish and sturgeon should be avoided.

Marine Animals That Aren’t Fish

The Torah’s fins-and-scales rule applies specifically to fish. Other sea creatures are categorically non-kosher because they are not fish at all — none of them have fins and scales, by definition.

Crustaceans: shrimp, lobster, crab, crayfish, prawns. None have scales. All non-kosher.
Mollusks: clams, oysters, mussels, scallops, squid, octopus, snails. None have fins or scales. All non-kosher.
Echinoderms: sea urchin (uni), sea cucumber, starfish. Not fish; non-kosher.
Cnidarians: jellyfish. Not fish; non-kosher.
Marine mammals: whale, dolphin, seal, sea lion, manatee. Mammals require shechita AND must have split hooves and chew cud, which marine mammals don’t. Non-kosher.
Amphibians and reptiles: frog, alligator, sea turtle. Not fish; non-kosher.

For a deeper dive into kosher sushi specifically — where shellfish and roe issues come up often — see the Kosher Sushi Guide.

Identifying Scales in Practice

At the fish counter, the simplest test is visual: look for visible scale flakes on the skin. If you can see distinct, overlapping plates, the fish is likely kosher. If the skin is smooth, slimy, or covered in tiny embedded denticles, treat it with suspicion until you can confirm the species.

A few practical situations:

Whole fish with skin on: Visible scales are the strongest evidence. Most Orthodox authorities consider this sufficient for fresh, unprocessed whole fish.
Fish fillets: Scales are removed during filleting. You can’t visually verify the species, so reputable certification (OU, Star-K, OK, CRC) or a known-reliable source becomes important.
Sushi: Salmon, tuna, yellowtail, mackerel, and snapper are kosher species, but a sushi restaurant’s kitchen may share equipment with shrimp, eel, and crab. Kosher certification or a dedicated kosher sushi restaurant is the safe path.
Smoked or canned fish: Always look for a kosher symbol. Additives, shared equipment, and oils derived from non-kosher sources are common issues.

Where the Major Kosher Authorities Agree (and Disagree)

The major American kosher certification agencies agree on the vast majority of species. The OU, Star-K, CRC, OK Kosher, and Chabad all accept the same core species lists. Disagreements tend to cluster on a small number of edge cases:

Swordfish — All major American Ashkenazi authorities (OU, CRC, Star-K) rule non-kosher. Some Sephardic communities historically permitted it.
Sturgeon and caviar — Orthodox authorities universally rule non-kosher. Conservative authorities have permitted it since 1969.
Buffalo fish and certain river species — Generally accepted as kosher when scales can be confirmed; occasional disputes turn on whether observed scales are cycloid or another type.
Roe (fish eggs) — Kosher only when from a kosher fish species. Caviar from sturgeon is non-kosher; salmon roe (ikura) and herring roe are kosher.
Anisakis worms in fish flesh — A separate halachic question. The OU and most contemporary poskim hold that anisakis worms originating in the flesh (rather than the digestive tract) are not the type of forbidden insect the Torah prohibits; some authorities are stricter and require visual inspection.

For fish-by-fish kosher status across nearly 300 species cross-referenced with these authorities, use the lookup at KosherFish.co.

Processing and Kosher Certification

Even a kosher species can become non-kosher based on processing. Equipment shared with shellfish or non-kosher seafood can render a product non-kosher. This is why canned or processed fish products benefit from a hechsher from the OU, OK, Star-K, or CRC.

A few specifics worth knowing:

Fresh whole fish with visible scales generally does not require certification — the visual identification is itself the certification.
Filleted fish at a non-kosher counter can be problematic if the same knives and surfaces are used for shrimp, shellfish, or non-kosher species. Many Orthodox consumers buy whole fish or use kosher-certified fish counters.
Canned tuna, sardines, salmon are technically from kosher species but may contain non-kosher oils, broths, or be processed on shared equipment. Look for an OU, OK, Star-K, or CRC symbol on the can.
Smoked salmon (lox) and gravlax need certification because smokehouses often handle non-kosher fish on the same equipment.
Imitation crab (surimi) is made from kosher fish (typically pollock) but always requires certification because of flavoring and processing concerns.

Fish Don’t Need Shechita — But Still Need Care

One important practical point: fish do not require ritual slaughter (shechita). Mammals and birds must be slaughtered by a trained shochet according to specific halachic procedures to be kosher. Fish are exempt from this requirement — the Talmud (Chullin 27b) derives this exemption from the same Leviticus passage that lists fins and scales as the only criteria. A kosher fish that died naturally, in a net, or by any other means remains kosher.

However, fish DO have their own concerns:

Bug check — Whole fish, especially when cleaning, should be inspected for parasites such as anisakis. Most contemporary authorities don’t consider in-flesh worms forbidden per Torah law, but reputable sources still recommend visual inspection.
Blood from fish — Unlike the blood of mammals and birds, fish blood is permitted to consume per the Talmud (Kritot 21b), with the caveat that one should not collect it in a way that suggests blood from non-kosher animals.
Mixing with dairy — Fish can be eaten with dairy (a salmon-and-cream-cheese bagel is kosher), but Ashkenazi custom traditionally avoids cooking or eating fish together with meat. This is a health-based custom (the Talmud cites a concern about tzara’at), not a Torah prohibition.

Frequently Asked Questions

Does a fish need both scales and fins to be kosher?

Yes. According to Leviticus 11:9–12, a fish must have both fins and scales. Since every fish with detachable scales also has fins, scales are the practical determining factor.

Is shark kosher?

No. Sharks have placoid scales embedded in the skin that cannot be removed without tearing it. These do not meet the halachic definition. Shark is not kosher according to all major Orthodox authorities.

Is swordfish kosher?

Under mainstream Orthodox practice, no. Adult swordfish lack qualifying scales. The OU rules it non-kosher. A small number of Sephardic authorities take a different view, but this is not the prevailing position.

Does canned tuna need kosher certification?

Yes. Tuna is a kosher species but canned tuna is processed on shared equipment and may contain non-kosher additives. Look for an OU or similar symbol on the can.

Do fish need to be slaughtered like other kosher meat?

No. Fish are exempt from the shechita (ritual slaughter) requirement that applies to mammals and birds. The Talmud (Chullin 27b) derives this exemption from the same Leviticus passage that defines kosher fish by fins and scales alone. A kosher fish remains kosher regardless of how it died.

Where can I check if a specific fish is kosher?

Use the lookup tool at KosherFish.co, or see the full species guide at The Complete Guide to Kosher Fish. The Orthodox Union also publishes detailed guidance on kosher fish at oukosher.org.