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How can you tell if a fish is Kosher?

by Rabbi Chaim Goldberg


Library » Mitzvot » Kosher » Kosher Creatures | Subscribe | What is RSS?


In this article, we will discuss two practical methods to determine if a fish is Kosher.1

The easiest way to determine if a fish is kosher, is by manually checking the fish for scales.2 Simply locate a scale on the side of the fish (preferably behind the gills, tail or fin – as mentioned by the Rama3 as a stringency to guarantee the scale did not fall off of another fish), grab it between your thumb and forefinger, and gently attempt to pull it out.

One should note that scales are always attached to the fish on the side closer to the head. The reason is fairly obvious if you can imagine how a fish swims. If the scale would be attached to the skin at the side closest to the tail, the current would pull the scale away from the skin and would inevitably rip it off as the fish swims.

Imagine an open umbrella in a brisk wind that is not pointed in the direction of the blowing wind. The umbrella would get caught in the wind and blow inside out. So too, the current would get caught under an inverted scale and rip it off, causing the fish to die due to infection.

The easiest way to determine if a fish is kosher, is by manually checking the fish for scales
After removing the scale, simply inspect the area where the scale came from and check if there is a rip in the skin. If the skin seems fairly undamaged, the fish is kosher. If the scale will not come out without the skin ripping, the scale is not a “kaskeset” (the biblical definition of a scale).

Generally speaking, it is fairly obvious if the skin ripped. As a practical way to get a sense of what skin normally looks like when a “kaskeset” is removed (and the skin does not rip) one could inspect the scaleless skin of fish which one knows to be kosher.

As long as a fish has “kaskeset” at some point in its lifecycle it is permitted and there is no requirement of “mesorah” (i.e. a tradition that identifies a particular fish as a kosher species).

Fish that lose their scales often have a single scale in the three areas mentioned earlier (behind the gills, tail and fin), though even without a scale present one could still recognize a kosher species of fish based on its skin.

The Darchei Teshuvah4 describes the possibility of determining the kosher status of a scaleless fish based on “mesorah”.

The “mesorah method” is derived from an idea mentioned in our previous article,5 namely that the Talmud tells us that a fish that has not yet grown “kaskeset” or lost its “kaskesket” is still a kosher species.

One should ask, even if theoretically true, how could one practically determine that the fish is kosher if there are no “kaskeset” on it now? The answer, says the Darchei Teshuvah, is that one can recognize the species based on its skin.

One may bring a fish whose “kaskeset” fell off or did not yet grow “kaskeset” but whose skin is still attached to someone familiar with the specific fish to determine if this is a species that is subject to a mesorah of being a kosher fish.

This “mesorah method” of determining kosher status is particularly useful when dealing with various types of mackerel. Mackerels tend to lose their scales when removed from the water, and the mesorah method can be used to permit the scaleless mackerel.


  • 1. See also "What is a kosher fish?" . (,2070155/How-can-you-tell-if-a-fish-is-Kosher.html)
  • 2. As discussed in the first part of this column , there is no practical requirement of checking for fins. (,2070155/How-can-you-tell-if-a-fish-is-Kosher.html)
  • 3. Rabbi Moses Isserles (Krakow, 1530-1572).
  • 4. Rabbi Tzvi Hirsh Schapiro, turn of the 20th century rabbi of Munkacz, Hungary.
  • 5. See footnote 2.


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Repentance. Or, more literally, "return" to G-d. Teshuvah involves regretting the past and making a firm resolution not to repeat the offense.
Usually referring to the Babylonian edition, it is a compilation of Rabbinic law, commentary and analysis compiled over a 600 year period (200 BCE - 427 CE). Talmudic verse serves as the bedrock of all classic and modern-day Torah-Jewish literature.
Literally means "fit." Commonly used to describe foods which are permitted by Jewish dietary laws, but is also used to describe religious articles (such as a Torah scroll or Sukkah) which meet the requirements of Jewish law.
Laws of Kosher (Jewish dietary laws).
According to Jewish law.
Beit Din
(Lit. House of Law). Rabbinical court.
It is forbidden to erase or deface the name of G-d. It is therefore customary to insert a dash in middle of G-d's name, allowing us to erase or discard the paper it is written on if necessary.
Supervisor. Usually a reference to the person hired by a rabbinical organization to supervise a facility to ensure its kosher status.