What makes a fish kosher? A great article from kosher.com, here’s a comprehensive FAQ on kosher fish.
Q: How do we identify a kosher fish?
A: The Torah (Vayikra 11:9) says that the simanim of kosher fish are snapir v’ kaskeses. However the Gemara (Chulin 66b) 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 fish that have scales have kaskeses. This is because the Ramban, in his commentary on the Torah, 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, Aruch HaShulchan 83:15) are not kaskeses. The Ramban’s definition is universally accepted, and in fact the Rema (Yoreh Deah 83:1) rules that those scales that cannot be easily removed (according to the parameters discussed below) cannot be called kaskeses.
Q: I heard there are several different scientific classifications of scales. Which are kaskeses?
A: Though scientists categorize scales by certain characteristics, 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. From the Torah’s perspective, the various classifications of scales are irrelevant. Statements by certain “experts” about various 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 scales, 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 scales can be properly removed. Kaskeses are attached on the side of the fish closer to the head and are not attached on the side closer to the tail. To remove them, one must grasp the side that is not attached and gently pluck it from the side of the fish. 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, identity is critical.
There are two ways to identify a kosher fish:
1. By removing a kosher scale from the skin. (The consumer need not personally remove the scale. The consumer only needs to see the scale removed and confirm that the skin did not rip from having the scale removed.)
2. By recognizing the fish as being from a kosher species. One can only recognize a fish species if the skin is still intact. It is generally impossible, even for a “maven”, to identify fish without skin. The exception to this rule is that the salmon and red trout fillets are accepted without skin, as there is no non-kosher fish whose flesh resembles that of a salmon or red trout.
For example, let’s say you want to purchase tilapia. (According to http://www.fishbase.org, there are more than 30 different species that could refer to tilapia. The U.S. Food and Drug Administration [the “FDA”] officially lists seven different tilapia that are marketed in the U.S.) You’ve heard that tilapia is a kosher fish, and the friendly counterperson assures you this skinless fillet is tilapia. You cannot rely on this person, unless he is both Torah observant and familiar with the laws of kosher fish.
Now let’s say a tilapia-eating friend (who met the above criteria) comes to the store with you and recognizes a fish in the display case whose scales have been removed as tilapia. Even though its scales are not present, you may eat this fish because a halachically reliable person has positively identified this as a kosher fish. Therefore, one can only purchase skinless fillets from a store under reliable rabbinic supervision.
Q: Why doesn’t the OU 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”. 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 in which 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 six different species of fish (see http://www.fishbase.org), 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. The OU 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:
1. You must bring a kosher cutting board as well, or have the store cover their cutting board, so that the fat of non-kosher fish on the board will not touch your fish. Make certain, as well, that the person cutting the fish washes their hands or changes their gloves before handling your kosher fish. (If the flesh of kosher 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].)
2. Be very familiar with the fish that you are buying, or check its kosher status personally before its skin is removed. One cannot use a kosher fish list to select a fish.
3. Be sure the employee who is working with your order does not mix non-kosher pieces of fish (or pieces that were not properly supervised) into your order.
4. One must be certain that the worker only uses the knife and board that you brought with you. This is particularly true when you do not bring a high-quality filleting knife, because it will be to the worker’s benefit to use the store’s knife, as the wrong knife is hard to work with. You cannot rely on a store that claims to have separate knives for kosher customers, unless the store has reliable kosher supervision.
5. Try to shop during the hours in which the store is less busy. Fish sellers will be more cooperative with the necessary requirements for a kosher order, as described above, if there are fewer customers waiting and the store is not being rushed to fill orders.
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.
If a fish is kosher, the eggs found inside of it are kosher. (Yoreh Deah 81:1.) 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 Yosef rules (cited in Shach 83:27) 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, the Orthodox Union and cRc accept 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 consumption in kosher kitchens. (Rabbi Y. Ephrati wrote this Psak in the name of Rabbi Y. Elyashiv in a Teshuva dated the 11th of Elul, 5763.) Despite resembling the non-kosher swordfish, 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. 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. 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.
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’yehudah (Sh’ailos and Teshuvos Nodah B’yehudah, Yoreh Deah Tinyana 28-30.) where he seems to permit an Astooriyan, which bears close resemblance (in its characteristics) to a sturgeon. The Pischei Teshuva (Yoreh Deah 83:1. 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.) and other later authorities take issue with the Nodah B’yehudah (who appears to be the single authority permitting this fish). The Orthodox Union and cRc regard 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. (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.)
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!