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Consumers’ FAQ’s on Kosher fish

Copyright © 2004 Union of Orthodox Jewish Congregations of America

by Rabbi Chaim Goldberg
Printed with permission of The Daf HaKashrus
Origionally printed in The Daf HaKashrus Volume 12 Issues 7 and 8

Q: How do we identify a kosher fish?

A: The Torah1 says that the simanim of kosher fish are “snapir v’ kaskeses”. However the Gemara2 tells us that all fish that have “kaskeses” have “snapir”, so in practice, all one needs to determine that a fish is kosher is that it has kaskeses!

Q: So what exactly is kaskeses?

A: “Kaskeses” is generally translated as scales. Nonetheless, not all scales are considered kaskeses. This is because the Ramban, in his commentary on the Torah3 tells us “kaskeses” are scales that can be easily removed by hand or with a knife without tearing the skin. Scales that are embedded in a fish (or are not visible to the naked eye)4 are not “kaskeses”. The Ramban’s definition is universally accepted, and in fact the Rema5 rules that those scales that cannot be easily removed (according to the parameters that will be discussed below) cannot be called “kaskeses”.

Q: I heard there a several different scientific classifications of scales. Which are kaskeses?

A: Though scientists categorize scales by certain characteristics,6 the Torah is only concerned with whether or not a scale can be easily removed without tearing the skin, irrespective of its shape, color or size.7 From the Torah’s perspective, the various scientific classifications of scales are irrelevant. Statements made by certain “experts” about certain types of scales always being kosher are not true.

Q: What are some examples of fish with scales that are not kosher?

A: Sturgeon definitely has scales8, but it is not kosher. Its scales are classified as “ganoid”, which means that they are covered with ganoin (similar in texture to fingernails) and cannot be removed without tearing the skin. Burbot has cycloid scales (one of the types often referred to as “always kosher”) yet because they are embedded, this fish is not kosher. Sand lances may have tiny scales, but since they are not visible, this fish is not kosher.

Q- How can I know if a fish is kosher?

A: To check if a fish is kosher, one must ascertain that its scales could be properly removed.9 Scales are attached on the side to the fish on that side of the scale which is closer to the head and are not attached on the other side of the scale which is closer to the tail. To remove the scales, one must grasp that side that is not attached and gently pluck it off from the side of the fish.10 If removing the scale did not damage the skin, then the fish is kosher.

Q- My local fish store is not under Rabbinic supervision, and it sells fillets without skin. How could I tell if the fish they are selling are kosher?

A: You cannot! Even if the fish is halibut, whitefish or carp (all kosher fish), once the skin is removed it is impossible to identify, and it cannot be assumed to be kosher. In determining the kosher status of fish, identifying the species is critical.

There are two ways to identify a kosher fish:

For example, let us say that you want to purchase tilapia.12 You heard that tilapia is a kosher fish, and the friendly counterperson assures you this scale-less fillet is tilapia. You simply cannot rely on this person, unless he is both observant in Torah and mitzvos and is familiar with the laws of kosher fish. Now let us say that a tilapia-eating friend (who is halachicly reliable) comes to the store with you and recognizes a fish in the display case whose scales have been removed (but the skin is still intact) as tilapia. Even though its scales are not present, you may eat this fish because a halachicly reliable person has positively identified it as kosher. Therefore, one can only purchase skinless fillets from a store under reliable Rabbinic supervision.

Q: What if only a patch of the skin is left on a fillet?

A: If you can have someone (halachicly reliable) confirm the identity of a fish based on a patch of skin, this would be sufficient.

Q: Why doesn’t the Orthodox Union just publish a kosher fish list?

A: At this time, there is no reliable consumer fish list, and it would be very difficult to create one.

The reason is that “common names” are a highly inaccurate way of describing a fish. For example, there are several fish known as “red snapper”.13 Who can say for certain that every fish called “red snapper” is in fact kosher, when “red snapper” could be referring to so many different fish? Another instance that we have found common names to be misleading is in the case of “Escolar”. Escolar could refer to Ruvettus pretiosus (kosher) or Gempylus serpens (non-kosher). Yet another is “Ling” which could refer to 6 different species of fish14 most of which are in fact kosher.  However when the OU examined a sample of one of these “Ling” fish whose Latin name is Lota Lota (also called Burbot, Freshwater Cod, Eelpout, Lawyer and other names) we found it to be not kosher.

Latin names are more accurate. We could theoretically create a list of kosher fish by Latin name. The problem is that fish sellers never refer to fish by Latin names, and have generally no knowledge of the correct Latin name for a fish! In one case, we asked a kosher fish store the Latin name of a certain (kosher) fish and the Latin name provided was that of a completely different, non-kosher fish!!!

Q: Can I bring my own knife to a non-certified fish store and have the workers prepare the fish for me?

A: Yes, but there are several issues to be aware of when doing this:

Q: What makes fish roe (eggs) kosher or non-kosher?

A: The eggs of fish have the same kosher status as the fish they come from, as do most foods that originate from a living creature.16 If a fish is kosher, the eggs found inside of it are kosher. Non-kosher fish, such as sturgeon, have non-kosher roe. Once roe is removed from a kosher fish (much like the flesh of the fish itself, after the skin is removed) it requires kosher supervision. Thus, even roe from a kosher fish could not be regarded as kosher unless it was under Rabbinical supervision from the moment of its extraction. The exception to this rule is red roe (i.e. from salmon or trout), which the Beis Yosef17 rules can be accepted as kosher without supervision (when processed in “dedicated” equipment and no ingredient other than salt is used.) The basis given for this leniency is that the Beis Yosef asserts that no non-kosher fish has red roe that remains red after salting. Though some have questioned the basis of this assertion,18 the Orthodox Union accepts the Beis Yosef’s ruling.

Q: Is it true that Blue Marlin is kosher?

A: Yes! Before the World Series Champions from Florida won the 2003 Major League Baseball Title, their mascot (whose Latin name is Makaira mazara) was approved for consumption19 in kosher kitchens. Despite resembling the non-kosher swordfish, (see below) Blue Marlin has the single requirement of a kosher fish; it has kaskeses.

Q: Besides shellfish, which are some common non-kosher fish to be aware of?

A: Catfish – (family Ictaluridae) lack scales entirely.20 Interesting for the kosher consumer to note, non-kosher catfish is reported to have a similar taste to the increasingly popular (and kosher variety of) tilapia.21 Catfish and tilapia fillets look almost identical, though catfish is notably cheaper. It is quite possible that an unscrupulous fish retailer might switch the two.

Basa or Tra (also called “China sole”) – (family Pangasiidae) are currently the subject of both nomenclature debates and antidumping litigation. Vietnamese importers were marketing them as catfish, to which they are nearly identical. Whether they are in fact catfish or not, they are not kosher.22

Sturgeon (family Acipenseriformes) as described earlier, its ganoid scales are not easily detached from its body, and thus are not “kaskeses”. A discussion about the kosher status of this fish can be found in a series of responsa from the Nodah B’yehudah23 where he seems to permit an Astooriyan, which bears close resemblance (in its characteristics) to a sturgeon. The Pischei Teshuva24 and other later authorities take issue with the Nodah B’yehudah (who appears to be the single authority permitting this fish). The Orthodox Union regards sturgeon as non-kosher.

Swordfish (Xiphias gladius) does not seem to have scales when one looks at a sample. Some say that it has scales that are embedded to such an extent that it is impossible to remove them without making a hole. Others say that it has kosher scales on parts of its body which fall off during its development. Still others claim that it may have some kosher scales even at the time of harvest. The Orthodox Union traditionally treats swordfish as non-kosher.25

Though your mother was right, and you should not judge a book by its cover, you should most certainly judge a kosher fish by its cover… its scales and identifying skin!


1 Vayikra 11:9.

2 Chullin 66b.

3 Vayikra 11:9.

4 Aruch HaShulchan 83:15.

5 Yoreh Deah 83:1.

6 For more information on the definitions of the various classifications of fish scales, see the Australian Museum’s web site at www.austmus.gov.au/fishes/students/scales/

7 Rabbi Y. Ephrati wrote this in the name of Rabbi Y. Elyashiv in a Teshuva dated the 11th of Elul, 5763 ( F-54).

8 More precisely scutes, which are technically defined as “enlarged scales often containing one or more bony projections.” See Peterson’s Field Guides Freshwater Fishes, 1991, Drs. Lawrence Paige and Brooks Burr.

9 Teshuvos She’vas Tzion #29 cited by Pischei Teshuva 83:1, states that it is necessary to actually remove the scales and not merely rely on the rov (i.e. majority) that most scales are easily removed.

10 I have not found this procedure explicitly, though this is simply the way to check the kosher status of a fish. Though the Nodah B’yehudah permitted a fish similar to sturgeon whose scales became removable only by soaking it in an alkaline solution, the Pischei Teshuva rules like the Teshuvos She’vas Tzion (cited above) who does not allow it.

11 The consumer need not personally remove the scale. The consumer only needs to see the scale removed and that the skin did not rip from having the scale removed. He must additionally be sure that the scale being removed was in fact attached to the fish before removal (and not that it was actually a scale from another fish which merely was stuck to this fish.)

12 According to www.fishbase.org, there are more than 30 different species that could be referred to as tilapia. The U.S. Food and Drug Administration (the “FDA”) officially lists 7 different tilapia that are marketed in the U.S., (see www.cfsan.fda.gov/cgi-bin/seafd?QUERY=tilapia) though there may be more. It is not possible for the Orthodox Union to ascertain that all species of tilapia are kosher.

13 See comments from the FDA on the species substitution of red snapper at www.fda.gov/bbs/topics/CONSUMER/CON00251.html.

14 See www.fishbase.org.

15If a piece of kosher skinless fish touches non-kosher fish oil, one cannot merely rinse the fish but rather must scrub it vigorously (referred to in halacha as shif-shuf gadol) or scrape the point of contact with a knife or stiff-bristled brush (referred to in halacha as graida).

16 Yoreh Deah 81:1.

17 Cited in Shach Y.D. 83:27.

18 See Aruch HaShulchan Y.D. 83:50 and Pri Chadash #26 cited there.

19 See footnote #7 above.

20 Peterson’s Field Guides Freshwater Fishes, 1991, Drs. Lawrence Paige and Brooks Burr.

21 Seafood Business Magazine, August 2003 issue.

22 For more on Basa and Tra see http://www.seafoodbusiness.com/buyguide/issue_basa.htm.

23 Sh’ailos and Teshuvos Nodah B’yehudah, Yoreh Deah Tinyana 28-30.

24 See footnote #9 above. See also Sh’ailos and Teshuvos Tzitz Eliezer 9:40 and 11:54 where he says explicitly that we cannot permit Sturgeon for several reasons.

25 See Sh’ailos and Teshuvos Tzitz Eliezer 9:40 who discusses a statement made by the Knesses HaGedolah about “cherev hadag” and explains why we cannot use the statement to permit swordfish.


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