TL;DR: A fish is kosher if it has both fins and scales — that’s the entire biblical test, drawn from Leviticus 11:9-12. salmon, tuna, cod, tilapia, herring, and most familiar species qualify. Shellfish, eels, catfish, and sharks do not. A few species like swordfish are contested. This guide explains how to verify any fish at the counter, what to do about processed products, and which authorities you can trust for the gray areas.
What Makes a Fish Kosher
The rules for kosher fish (kashrut) are simpler than for any other food category. There is one test, given directly in the Torah, and it has two parts: the fish must have snapir (fins) and kaskeses (scales). If a fish has both, it is kosher. If it lacks either one, it is not. There is no requirement for ritual slaughter the way there is for meat, and there are no restrictions on how kosher fish may be cooked or combined with other ingredients (with one important exception covered below).
This makes fish one of the most accessible categories of food for someone newly keeping kosher, or for anyone hosting kosher guests. You don’t need a hechsher (kosher certification symbol) on the package to know that a whole salmon is kosher — you can see the fins and scales yourself.
The Torah Source: Leviticus 11:9-12
The rule comes directly from the book of Leviticus, in the JPS translation:
“These you may eat, of all that are in the waters: anything in the seas or the streams that has fins and scales, these you may eat. But anything in the seas or the streams that has no fins and scales, of all the swarming creatures in the waters and of all the living creatures in the waters, is detestable to you. You shall regard them as detestable; you shall not eat their flesh, and you shall regard their carcasses as detestable. Everything in the waters that does not have fins and scales is detestable to you.” [Lev. 11:9-12]
A parallel passage in Deuteronomy 14:9-10 repeats the same rule. Both passages agree: two criteria, no exceptions, no further elaboration in the Written Torah.
The Two Criteria: Fins AND Scales
The Mishnah, which records the Oral Torah’s elaboration on the biblical rules, makes an important observation in tractate Chullin 3:7: any fish that has scales also has fins. This means in practice you only need to verify scales — fins come automatically. The Talmud (Niddah 51b) confirms this principle.
Not just any scales count. The halachic definition requires scales that can be removed from the skin without tearing the flesh underneath. This excludes “placoid” scales — the tooth-like dermal denticles found on sharks and rays, which are embedded into the skin itself. Rambam codifies this in Mishneh Torah (Hilchot Ma’achalot Asurot 1:24), and the Shulchan Aruch (Yoreh Deah 83) follows suit.
The scale types that DO count are “ganoid” (found on sturgeon and gar — though sturgeon is contested for separate reasons, see below), “cycloid” (most bony fish — salmon, herring, carp), and “ctenoid” (the comb-like scales on perch, bass, and many others).
Common Kosher Fish
The following species appear on every major kosher authority’s approved list (OU, CRC, Star-K). This is a starting reference, not exhaustive — the OU’s full kosher fish list at oukosher.org covers hundreds of species.
- Salmon — all species: Atlantic, Sockeye, Coho, King (Chinook), Pink
- Tuna — Yellowfin, Bluefin, Albacore, Bigeye, Skipjack (canned tuna typically requires a hechsher because processing equipment is shared with non-kosher fish)
- Cod — both Atlantic and Pacific
- Tilapia — most commonly farmed varieties
- Trout — Rainbow, Brown, Brook
- Sea Bass — true sea bass species; note that “Chilean sea bass” is actually Patagonian toothfish, which has scales and is kosher
- Mahi Mahi (Dorado)
- Flatfish — Flounder, Halibut, Sole
- Snapper — Red, Yellowtail, and most other species in the snapper family
- Forage fish — Herring, Sardines, Anchovies (whole-fish verification is easier here)
- Mackerel — Atlantic, Pacific, Spanish, and King mackerel are kosher
- Whitefish (Lake Whitefish) — traditional gefilte fish ingredient
- Pike and Pickerel — also traditional gefilte fish base
- Carp — completes the classic Ashkenazi gefilte fish trio
- Bass — Striped Bass, Largemouth, Smallmouth
Common Non-Kosher Aquatic Species
These are prohibited because they lack fins, scales, or both [Lev. 11:10-11]:
- All shellfish — shrimp, lobster, crab, crayfish, scallops, oysters, clams, mussels (no fins or scales)
- Cephalopods — octopus, squid, cuttlefish
- Eels — lack the proper scale type
- Catfish — no scales
- Shark — placoid scales (dermal denticles) don’t qualify [Rambam, Hilchot Ma’achalot Asurot 1:24]
- Monkfish, Anglerfish — no scales
- Marlin, Sailfish — generally prohibited by Orthodox authorities
- Frogs, turtles — these are amphibians and reptiles, not fish, and are non-kosher under separate Torah categories
The Contested Species: Swordfish and Sturgeon
Two species deserve their own section because authorities genuinely disagree about them.
Swordfish
Juvenile swordfish have scales that drop off in adulthood. The historical OU position, going back decades, has been that this counts — the fish had scales at some point in its life, satisfying the criterion. Conservative-leaning authorities (CRC and most Sephardic poskim) disagree: the scales must be present, not formerly present. Today, most kosher consumers in the US treat swordfish as a personal-rabbi question rather than a settled answer. If you keep your rabbi’s halacha, ask them.
Sturgeon (and caviar)
Similar issue — adult sturgeon’s scales aren’t easily removable in the traditional sense. Reform authorities have permitted sturgeon; Orthodox authorities (across all major schools) prohibit it. This means traditional sturgeon caviar is not kosher under Orthodox standards. Kosher caviar exists — it’s typically made from kosher fish like salmon, whitefish, or trout roe — but check the hechsher to be sure.
At the Fish Counter: How to Verify
If you’re buying whole fish with the skin on, you can verify kashrut yourself: look for scales you can lift with a fingernail without tearing the skin. That’s the test.
For fillets, this gets harder. Skinless fillets are visually identical between species — there’s no way to tell salmon from non-kosher fish by looking at a fillet. You have three options:
- Buy from a certified kosher fishmonger — they handle only kosher species, with separate equipment
- Buy packaged fillets with a hechsher — OU, OK, Star-K, CRC, or Kof-K on the label
- Buy fillets with the skin still attached — you can verify scales on the underside
At a regular supermarket, the skin-on rule is the most practical. Ask the fishmonger to leave the skin on, even if you plan to remove it at home.
Processing Concerns: Smoked, Canned, and Cured
Any fish that has been processed — smoked, cured, canned, or transformed into stock or fumet — requires a kosher certification on the packaging. Reasons:
- Shared equipment — smokers, canning lines, and stock kettles often process both kosher and non-kosher fish
- Additives — flavorings, preservatives, and oils may not themselves be kosher
- Wine and dairy concerns — some fish products include wine-based flavorings or dairy ingredients
The major hechsher symbols to look for: OU (Orthodox Union, the most widely accepted), OK, Star-K, CRC (Chicago Rabbinical Council), and Kof-K. Many local Vaads also issue reliable certifications — accepted standards vary by community.
One Important Exception: Fish and Meat
Fish is pareve (neither meat nor dairy), which would suggest it can be eaten with either. There’s one significant Ashkenazi custom, codified by the Rama in his glosses on the Shulchan Aruch (Yoreh Deah 87:3): do not eat fish and meat together in the same dish or at the same time. The custom requires using separate utensils, and rinsing one’s mouth or eating bread between courses. Sephardic communities historically did not adopt this restriction with the same stringency. If you keep Ashkenazi custom, plan menus with this in mind — gefilte fish as an appetizer course before a meat main is fine, served on separate plates.
Frequently Asked Questions
Is shellfish ever kosher under any circumstance?
No. Shellfish lack both fins and scales, so they fail the two-criteria test in Leviticus 11:10-11 outright. No preparation, blessing, or substitution makes them kosher. Vegan or fish-based imitation crab, lobster, or shrimp can be kosher if produced under hechsher.
Why does canned tuna need a hechsher if tuna is kosher?
The fish itself is kosher, but canned tuna is processed on shared equipment that also handles non-kosher fish. The cans, oil, broth, and packing additives may also include non-kosher components. A hechsher confirms that all elements meet kashrut standards [per OU kosher fish list guidance].
Is fish roe (caviar) kosher?
Roe is kosher if it comes from a kosher fish. Salmon roe (ikura), whitefish roe, and trout roe are kosher under standard Orthodox standards when bearing a hechsher. Sturgeon caviar — the traditional luxury product — is not kosher under Orthodox standards because sturgeon is itself non-kosher.
Can I eat fish at a non-kosher restaurant?
Strict interpretations say no, because of equipment cross-contamination (the same grill cooked shrimp earlier, the same knife cut shellfish). Lenient interpretations permit ordering a clearly-kosher whole fish prepared simply, on the understanding that the species is verifiable. Most Orthodox authorities encourage erring on the strict side; most Conservative authorities permit the leniency. Ask your rabbi for your specific community’s standard.
Is gelatin from fish kosher?
Fish-derived gelatin (used in some kosher gummies, marshmallows, and capsule supplements) is kosher when it comes from kosher fish and carries a hechsher. It avoids the kashrut complications of bovine or porcine gelatin. Look for “kosher fish gelatin” or a hechsher confirming the source.
What about fish stock and fish oil supplements?
Both require a hechsher. Fish stock concentrates may include extracts from non-kosher fish; fish oil supplements (omega-3, cod liver oil) are processed in facilities that may handle non-kosher species. The hechsher confirms source and processing line.
Where to Go From Here
Now you have the framework. If you want to go deeper:
- For specific authority lists: OU kosher fish list and CRC fish list
- For Torah text: Sefaria — Leviticus 11
- For practical halacha on disputes: ask your rabbi (the right authority for any borderline case is always the one who knows your community’s standard)
The biblical test is two criteria. Everything else — processing, certifications, the disputed species — flows from those two words: snapir and kaskeses. Fins and scales. Verify those, and you’ve covered the foundational kashrut question for any fish you’ll encounter.
