Ask the Expert: Fins and Scales

How can you be sure a fish is kosher?

Question: I know that kosher fish need to have fins and scales, but then how can codfish possibly be kosher? I grew up on Martha’s Vineyard, and I saw a lot of codfish, fresh out of the ocean. Their skin is as smooth as a baby’s tush — not a scale to be found. What’s the story?
–Sara, Brookline

Answer: I am an expert on many things, Sara, but codfish is not on that list. So I consulted with Michelle Jost, of the John G. Shedd Aquarium in Chicago. Michelle assures me that all species of cod have cycloid scales, like most members of the Gadidae family. Cycloid scales have a smooth outer edge, and that might be part of the reason that you couldn’t see them on the apparently very sleek codfish exterior.

But, as you’ve pointed out, determining whether a fish has fins and scales isn’t always so simple.

The ruling about kosher fish comes from Leviticus 11:9, “These you may eat of all that live in water; anything in water, whether in the seas or in the streams, that has fins and scales–these you may eat.”

The Mishnah in Niddah 6:9 explains that all fish that have scales also have fins. Therefore, any fish with scales is kosher. This theory is reiterated in the Gemara (Hullin 66b). But scales can be a complicated matter in their own right. Some fish are born with scales that fall off as they get older. Other fish have scales that are only visible with a microscope. So is there any foolproof method for telling if a fish is kosher?

Right here on My Jewish Learning we have a list of kosher fish. These are fish that are known to have scales (and thus fins) and so are generally accepted as kosher.

But a list isn’t always sufficient. There are some (mostly Orthodox) rabbinic authorities who worry that a non-kosher fish might be (inadvertently or intentionally) marketed as being kosher. So someone who’s trying to buy a pound of whitefish might accidentally buy a similar-looking fish that does not have scales. How to avoid this situation?

The Webbe Rebbe, over at the Orthodox Union, advised me to simply ask the man (or woman) at the fish counter to remove a scale on the spot. If the scale comes off easily, without ripping the flesh of the fish, then the fish can be considered kosher.

Interestingly, sturgeon and swordfish fall into the category mentioned earlier–fish that have scales when they’re young, but lose them as they get larger. Because there is no scale to pull off that could prove the fish’s kashrut, most Orthodox rabbinic authorities say that these fish are not kosher. However, after consulting with a number of marine biologists, the Conservative Movement‘s Committee on Jewish Law and Standards has ruled that swordfish and sturgeon are kosher.

So you see, this fins and scales business is more complicated than it might seem. Next time you’re at a fish counter (or back at your childhood home) see if you can get some up-close-and-personal face time with a cod, and I bet you’ll find it to be both smooth and scaly. Until then, may I recommend this trout recipe that is more eco-friendly than cod and also tastes pretty snappy when made for a Shabbat meal?

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