Non-Kosher Fish: The Complete Guide to What You Cannot Eat and Why

Understanding which fish are not kosher is just as important as knowing which ones are. Whether you are new to keeping kosher, planning a menu for guests who observe, or simply want a reliable reference, this guide covers the full picture — the rule, the specific categories of non-kosher fish and seafood, the edge cases, and the practical realities.

The Rule: fins and scales, Both Required

The kosher standard for fish comes from Leviticus 11:9-12 and Deuteronomy 14:9-10. The rule is clean and consistent: a fish is kosher if and only if it has both fins and scales. Both. Not one or the other.

Several important details follow from this rule. First, it applies at the species level — an entire species is either kosher or not based on its biology. Second, halacha requires that scales be removable without tearing the skin of the fish. A fish whose “scales” are fused to the skin or are technically a different structure does not qualify. Third, shellfish and other sea creatures that are neither fish nor have fins and scales are entirely excluded.

Shellfish: Crustaceans

Crustaceans have no fins and no scales. Every crustacean is non-kosher. This category includes:

shrimp and prawns (all species)
Lobster
Crab — blue crab, Dungeness crab, king crab, snow crab, and all other species
Crayfish (also called crawfish or crawdads)

Mollusks

Mollusks are marine animals that are entirely non-kosher. They have no fins and no scales:

Clams, oysters, mussels, scallops
Squid and calamari
Octopus
Abalone

Scaleless Fish

Some creatures are anatomically fish — they have fins, they swim — but lack true removable scales. These are non-kosher:

Catfish — All species, including swai, basa, and pangasius. Catfish has smooth skin without scales.
Shark — Most shark species have dermal denticles, which are tooth-like skin structures rather than true removable scales. All common shark species are non-kosher.
Eel — All species of eel, including freshwater eel (unagi, used in teriyaki eel at sushi restaurants) and moray eel, lack true removable scales. Eel is non-kosher.
Sturgeon — Sturgeon has scutes and ganoid scales, which are bony plates fused to the body and cannot be removed without damaging the flesh. Under the halachic removability test, sturgeon fails. The overwhelming majority of Orthodox authorities rule sturgeon as non-kosher. This also makes caviar from sturgeon — including beluga caviar — non-kosher according to most Orthodox authorities.
Lamprey — An eel-like jawless fish with no scales. Non-kosher.

Controversial Cases

Swordfish — Adult swordfish do not have scales. Juvenile swordfish have scales that are shed as the fish matures. Orthodox authorities rule swordfish as non-kosher because the fully grown fish used for food lacks scales. The Conservative movement has ruled swordfish kosher based on the juvenile scales.

Sturgeon caviar — As noted above, most Orthodox authorities consider sturgeon non-kosher due to the ganoid scale issue. There is a small minority halachic opinion that permits sturgeon, but standard kosher observance treats sturgeon and its roe as non-kosher.

The Species Is Not the Whole Story

Even a fully kosher fish species can become non-kosher based on how it is handled. A piece of salmon cooked in a pan previously used for shrimp, or baked in an oven alongside lobster, has been rendered non-kosher through the non-kosher equipment. A tuna roll made at a non-kosher sushi bar — even though tuna is a kosher species — is non-kosher because of the kitchen it was prepared in.

The species being kosher is a necessary condition, but not sufficient. Preparation, equipment, ingredients, and supervision all matter. This is why kosher certification from a recognized agency is essential for restaurant dining and prepared fish products.

A Quick Reference

If you need a fast checklist of what is not kosher in the seafood category:

All shrimp, prawns, lobster, crab, and crayfish — non-kosher
All clams, oysters, mussels, scallops, squid, octopus, and abalone — non-kosher
Catfish, shark, eel, sturgeon, and lamprey — non-kosher
Swordfish — non-kosher under Orthodox standards
Sturgeon caviar, including beluga — non-kosher under most Orthodox authorities
Any kosher fish species prepared in a non-kosher kitchen — non-kosher

When in doubt, stick to well-known kosher fish — salmon, tuna, tilapia, flounder, cod, trout, snapper — purchased from a kosher source or with reliable certification on the package. The restrictions, while real, leave an enormous range of excellent options on the table.