Kosher Aquatic Life: Fins and Scales
The dietary laws concerning aquatic life are characterized by a unique structural simplicity compared to the laws governing land animals or birds. While land animals require a combination of physical traits and specific species identification, and birds rely on a list of exclusions, the Torah provides a streamlined, binary criterion for water-dwelling creatures. Leviticus 11:9-12 establishes that any creature living in the waters—whether in seas or rivers—must possess two specific physical features to be permissible for consumption: fins (snapirim) and scales (kashkashim).
The Biblical Definition of Aquatic Permissibility
The text of Leviticus 11:9 explicitly states:
"These you may eat of all that are in the waters: everything that has fins and scales in the waters, in the seas, and in the rivers, those you may eat."
The repetition of "in the waters" serves to include all types of aquatic environments, ranging from large oceans to small freshwater streams. If a creature lacks either of these two features, it is categorized as "sheketz" (an abomination or detestable thing).
The term snapirim refers to the (plural) locomotor organs of the fish, which provide stability and direction.
The term kashkashim refers to the (plural) protective plating or skin covering.
The presence of both is the absolute requirement. Unlike land animals, where the Torah lists specific species like the camel or the pig to illustrate exceptions, the section on fish focuses entirely on these two biological markers. If a fish possesses both fins and scales, it is inherently kosher, regardless of its species name or its predatory habits.
The Halakhic Relationship Between Fins and Scales
A critical principle established in the Mishnah (Niddah 6:9) and further explored in the Talmud (Chullin 66b) is the biological correlation between these two markers.
It is written: “Whatever has fins and scales in the waters, in the seas, and in the rivers, you may eat them” (Leviticus 11:9). There is a principle with regard to the signs indicating that fish are kosher: Any fish that has scales has fins; and there are fish that have fins but do not have scales. Similarly, with regard to kosher animals it is written: “Whatever parts the hoof, and is wholly cloven-footed, and chews the cud, among the beasts, that you may eat” (Leviticus 11:3). Any animal that has horns has hooves; and there are animals that have hooves but do not have horns.
§ The Sages taught in a baraita: The Torah states the prohibition of non-kosher fish both positively and negatively: “These may you eat of all that are in the waters: Whatever has fins and scales…them you may eat. And all that have not fins and scales…they are a detestable thing unto you” (Leviticus 11:9–10). From the implication of that which is stated: Eat fish that have these signs, I would derive the inverse: Do not eat fish that do not have them. And from the implication of that which is stated: Do not eat fish that do not have them, I would derive the inverse: Eat fish that have them. If so, why did the Torah teach both of them? It is in order to indicate that one who eats non-kosher fish transgresses, on its account, both a positive mitzva and a prohibition.
The Sages observed that all fish that have scales also have fins. However, there are fish that have fins but do not have scales. Consequently, the presence of scales becomes the primary diagnostic tool for determining the kosher status of a fish. If you find a piece of fish with scales, you can be certain it also possessed fins in its natural state, making it permissible.
This observation simplifies the process of identification but does not remove the requirement for both. The legal reality remains that both fins and scales must exist. The "scales" mentioned must meet specific criteria to be considered halakhically valid.
According to the Ramban (Nachmanides), the definition of kaskeset requires that the scales be removable from the skin of the fish. If the scales are so deeply embedded or fused to the skin that they cannot be removed without tearing the skin itself (as is the case with sturgeon or shark), they are not considered "scales" in the biblical sense. This distinction is vital in modern food science and kashrut certification.
Ramban on Leviticus 11:9:1
SNAPIR V’KASKESES’ (FINS AND SCALES). “Snapirim — these are what [the fish] swim with. Kaskeses — these are the scales attached to [the body of the fish].”
This is Rashi’s language, and so also it is found in the Gemara of Tractate Chullin. But you should not [be led to] understand from their language that these scales are really [inflexibly] fixed to their bodies and attached to the skin of the fish [so that they do not come off at all]. Rather, they are called “fixed” because they do not move to and fro from the fish, nor do they quiver as do the fins. They are the round coverings, the plates of which are like finger-nails, and they can be removed from the skin of the fish by hand or knife. But those [scales] which are fixed and attached to the skin of the fish and cannot be removed from the skin at all, are not kaskeses (scales), and the fish [which has them] is prohibited food. It is for this reason that the Sages in the Gemara said that “Kaskeses is the cover of the fish.”
In the words of the Tosephta: “The kaskasim are those [objects] which cover the fish, and the snapirim are those with which the fish moves.” This is also the translation of Onkelos, who rendered the word kaskeses as klippin, [which means literally “shells”], for they are the “shells” of the fish which can be taken off and peeled away like the bark of trees and the peel of fruits. Such is also the meaning of the verse stating, and he [Goliath] was clad with a coat of ‘kaskasim’, for all their [war-] coats were made of rings, and some people made “scales” in them in order to close up the openings of the rings, so that thin arrows should not be able to penetrate them, and it was those “scales” that were called kaskasim.
The Sages also mentioned them in the Gemara [Tractate Sanhedrin] in the Chapter Cheilek: “Dressed in coats of mail made with scales.” Now Jonathan the son of Uziel translated [in the above-mentioned verse concerning Goliath that he was clad with] “a coat of galbin,” this being of the expression, the razor of ‘hagalabim,’ which are “leather workers.” [By so translating, Jonathan thus] intended to say that the covering at the openings of the rings in this coat of mail was like that of the scales on a skin of a fish, as they used to boil hard skin and cover the coats of armor with them, a practice they do to this day. Understand this.
The reason why fins and scales [are signs of permissibility as food] is that those fish which have them always dwell in the upper clear waters, and they are sustained through the air that enters there. Therefore their bodies contain a certain amount of heat which counteracts the abundance of moistness [of the waters], just as wool, hair and nails function in man and beast.
Those fish which have no fins and scales always dwell in the lower turbid waters, and due to the great abundance of moistness and gatherings of water there, they cannot repel anything. Hence they are creatures of cold fluid, which cleaves to them and is therefore more easily able to cause death, and it [the cold fluid] does in fact cause death in some waters, such as stagnant lakes.
(Commentary on the Torah by Ramban (Nachmanides). Translated and annotated by Charles B. Chavel. New York, Shilo Pub. House, 1971-1976. Source: nli.org.il. Digitization: Sefaria)
Biological Identification and Modern Taxonomy
Applying ancient biblical terminology to modern marine biology requires precise definitions. In the context of Jewish law, a scale is a "kaskeset" only if it is visible to the naked eye and can be removed by hand or with a knife. This usually refers to ctenoid or cycloid scales, which are found on common kosher fish like salmon, tuna, carp, and tilapia.
Conversely, placoid scales—the tiny, tooth-like structures found on sharks—are functionally part of the skin and do not qualify. Similarly, the bony plates found on sturgeon (ganoid scales) are often considered problematic because they are difficult to remove without damaging the flesh. This illustrates the gap between purely biological definitions, where a shark is said to have "scales," and the halakhic definition, which requires the scales to be a separate, removable covering.
The Status of Shellfish and Other Marine Life
The Torah's criteria automatically exclude several large categories of aquatic life. Because the requirements are specifically fins and scales, the following are prohibited:
Crustaceans: Shrimp, lobster, crabs, and crayfish lack both fins and scales.
Mollusks: Clams, oysters, mussels, and scallops are excluded.
Cephalopods: Octopus and squid, despite being "swimmers," do not possess the required markers.
Marine Mammals: Whales and dolphins, being mammals that live in the water, do not have the required signs and are strictly forbidden.
Bottom Feeders and Eels: Species that are smooth-skinned or possess only microscopic, non-removable scales are classified as non-kosher.
The classification of "sheketz" for these creatures is significant. While the prohibition of non-kosher land animals uses the term "tamei" (impure), the use of "sheketz" for non-kosher fish emphasizes a sense of revulsion. This terminology reinforces the boundary between the Israelite diet and the common practices of surrounding seafaring cultures of the ancient Near East.
Ibn Ezra on Leviticuss 11:10:1
OF ALL THAT SWARM IN THE WATERS. They are the small creatures that were created from the water. The waters contain living creatures that are both male and female. After stating they are a detestable thing unto you Scripture goes on to say, and they shall be a detestable thing unto you (v. 11) in order to explain in what way they shall be detestable namely, ye shall not eat of their flesh (Ibid.). Note, fish are called flesh. However, what the sages of blessed memory said with regard to vows refers to the custom of their generations. Scripture adds, Whatsoever hath no fins nor scales to include all waters, for Scripture earlier mentioned only the seas and the rivers.
Swordfish and Tuna: The Scale Debate
The application of these laws has led to historical and contemporary debates regarding specific species, most notably the swordfish. A kosher fish must have its scales for at least a portion of its life cycle. It does not necessarily need to retain them until it is caught. For instance, some species of tuna lose most of their scales as they mature or during the struggle of being caught, yet they remain kosher because they possess them at some stage.
The swordfish presents a more complex case. While juvenile swordfish possess scales, they lose them as they reach adulthood. In earlier centuries, many authorities permitted swordfish based on the presence of scales in the young.
However, in the mid-20th century, many kashrut agencies moved toward a more stringent position, arguing that the "scales" found on juvenile swordfish do not meet the legal definition of kashkashim because they are more like bristles or embedded spikes. This demonstrates how traditional law interacts with evolving anatomical observations.
The Concept of Ichthyological Integrity
Because fish do not require ritual slaughter (shechita) like land animals or birds, the primary concern in kashrut is the integrity of the species. As long as the fish is dead, it is potentially edible, provided it is a kosher species. In a modern marketplace, this creates a challenge: once a fish is filleted, it is often impossible to identify the presence of scales.
Halakhic authorities generally require that a piece of skin with at least one identifiable scale remain attached to the fillet for it to be accepted as kosher without a specific certification. This physical evidence serves as a "seal of identity," ensuring that a cheaper, non-kosher whitefish hasn't been substituted for a kosher variety. This practical application of the law links the ancient requirement of kashkashim directly to modern consumer protection and food safety in a Jewish home.
Philosophical and Symbolic Perspectives
While the primary focus of this study is the legal and linguistic framework, the choice of fins and scales has invited significant commentary regarding the symbolic nature of the kosher fish. The Sages of the Talmud and later thinkers like the Kli Yakar suggest that these two features represent movement and protection.
Deuteronomy 14:9 - Kosher fish: fins and scales?
The Midrash (Vayikra Rabbah 13:3) teaches that kosher laws elevate our eating to a holy act. Fish with fins and scales represent positive traits - scales symbolize protection from negative influences, while fins represent the ability to move forward spiritually (Kli Yakar on Vayikra 11:9)
Fins allow the fish to propel itself forward, resisting the current, while scales act as a suit of armor against the environment. This is often compared to the spiritual life of an individual: the ability to move against the "current" of popular culture and the necessity of maintaining a protective "outer shell" of law and tradition to preserve one's inner integrity. While these are homiletic interpretations (aggadah), they reflect the Jewish tradition's attempt to find meaning in the specific physical requirements set forth in Parsha Shemini. The fish is not merely a food source but a creature whose very anatomy signals a specific mode of existence—one defined by the boundaries of the Law.
Am Yisrael Chai!
Kimberly Davis
Contributors: Our Great Sages
Ramban (Nachmanides)
Rashi
Onkelos
Jonathan the son of Uziel
Ibn Ezra
Kli Yakar