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Scaleless Carp


Genetic engineering has opened the world of kashrus to new levels of discussion. Is the scaleless carp a kosher fish? Scaleless carp were originally developed in Germany for ease of cooking. In 1904, the scaleless carp became an export item. Can a species that originally had scales still be considered kosher without them? What is the status of a non-kosher fish which underwent a genetic mutation to make it grow scales? Is there a kosher eel? Can a scale-less species which could grow scales in certain environments be considered kosher? Is genetic engineering permitted? Hybridization is an age-old agricultural practice attempting to create superior produce. Is this branch of science permitted? Of this and more in the coming article.

Kosher Species

In this week’s parasha we read: “Among all [creatures] that are in the water, you may eat these: Any [of the creatures] in the water that has fins and scales, those you may eat, whether [it lives] in the waters, in the seas or in the rivers. But any [creatures]that do not have fins and scales, whether in the seas or in the rivers, among all the creeping creatures in the water and among all living creatures that [live] in the water, are an abomination for you. And they shall be an abomination for you. You shall not eat of their flesh, and their dead bodies you shall hold in abomination” (Vayikra 11:9-12). Fish are considered kosher if they have two kashrus signs: scales and fins. The Mishna (Niddah 51b) notes that the two are actually one – only scales, since no species of fish exists with scales and without fins. As a result, all scaled fish are considered kosher.

Could a species that underwent genetic engineering and therefore has no scales still be considered kosher? And can a similarly treated non-kosher fish with scales be considered kosher? What happens if the resulting creature has scales but no fins?


This question is not merely theoretic. One of the most popular fish in Israel is the carp, originally brought over from Yugoslavia nearly 100 years ago. The original species was covered with large prominent scales. Some 50 years ago, fish farmers began breeding carp with other species in attempt to produce a fish that was easier to clean. Over the years, along with genetic engineering, fish farmers now can raise carp that only have one or two lines of scales. Some fish can even be born with no scales at all. Another strain – the Scaleless Carp, (Doitsu or Koi) — originally from Germany, has no scales at all.

The incentive to produce a scaleless fish is understandable – scales raise the price of cleaning the fish significantly, and are a major headache for factories and housewives alike, besides for the various diseases fish can catch in their scales.

Due to the kosher consumer’s concerns, producers are careful to ensure fish retain a line or two of scales, but the question remains – could the same species without scales still be kosher? Is buying it permitted? And what can be done if after purchasing it, a fish is found to lack scales?

Indicator or Cause

Rabbi Bakshi Doron (Binyan Av II, 42) discusses this issue and points out that the answer is rooted in a much early dispute: is the kashrus sign mentioned in the Torah and Gemara indicative of a kosher species, or do they actually make the animal kosher? Does the Torah forbid eating non-kosher animals and provide us with a sign to recognize them, or do the signs actually make them kosher, in which case the same species without the kosher sign would be unkosher?

Rav Bakshi Doron does not issue a verdict on this issue, neither does Rav Moshe Sternbuch in his discussion in Teshuvos V’hanhagos V, 247. He writes that since this topic was disputed by the Rishonim we must be stringent both ways.

Non-Kosher Turns Kosher

The Yereim (131) notes a tradition deeming predatory or scavenger birds unkosher. Shevet Halevi (VII, 121) cites the Chasam Sofer (Chulin 61b) as understanding that according to the Yereim if the common chicken would change its behavior and become a bird of prey, it would no longer be kosher because the behavior is the determining factor. And conversely, if it would go back to its original disposition it would return to its original kosher status.

Rav Wosner, however, understands the Yereim differently: in his opinion a kosher species is forever kosher, no matter what changes it underwent over the years, and the Yereim’s tradition only applies when attempting to determine the kosher status of an unknown species.

Animal Changes

Rav Wosner furthermore, differentiates between natural changes that occur in animals like beginning to grow scales or eating prey, and human intervention that prompts them. In his opinion, even the Chasam Sofer would agree that if it is only a genetic mutation that prevents a fish from producing scales it remains kosher.

Additionally, he differentiates between the kosher signs and inherent factors. Chazal passed the tradition on birds as the most noteworthy inherent nature of non-kosher fowl. Therefore, any type of  bird seen predating or scavenging would be considered not kosher, according to the Chasam sofer’s understanding of the Yeraim, because doing so displays the nature of non-kosher birds. Scales, however, are just the sign of a kosher fish species, not an inherent nature. As a result, if one fish of the same species known as kosher happens to be born without scales, it can still be seen as kosher.

And the opposite, too, is true according to Rav Wosner – shrimp or eel that due to genetic engineering grow scales remain unkosher.

Practically, though, Rav Wosner maintains that the scaleless carp should not be accepted as kosher because it could create mix-ups, ending with us no longer being able to differentiate between a kosher and non-kosher fish. As a result, people might mistakenly eat non-kosher seafood.

Interfering with Nature

Rav Wosner criticizes scientists who use their intelligence to interfere with nature, explaining that changing G-d’s creation is forbidden and goes against G-d’s Will. G-d’s world was created complete and perfect and has everything in it to allow us to fulfil our mission. Interfering in it is akin to the prohibition of Kishuf or witchcraft. Kishuf, explain Chazal (Chulin 7b) is forbidden because it goes against the Divine Will, similar to the prohibition of kilayimm (planting certain mixtures of seeds; grafting; mixing plants in vineyards; crossbreeding animals; formation of a team of different kinds of animals working together; mixing wool with linen in garments).

Leather Carp

Rabbi Menashe Klein of Ungvar discusses a species of carp called Leather Carp, another variation produced through biological intervention. This method utilized radiation to cause the fish to be born without scales. He records that he discussed this issue extensively with Rav Elyashiv, concluding that if the fish originated from a kosher fish’s egg the result is kosher and the fish remains a carp, which is a kosher species. In his opinion the process here is similar to that used to produce seedless grapes. He does, nevertheless, discourage all involvement in this kind of scientific activity which involves the prohibition of kilayim.

Practically, though, the Leather Carp remains prohibited due to other reasons — so people should not get mixed up and come to eating other, non-kosher, scaleless fish. This prohibition is similar to Chazal’s prohibition against drinking fish blood — so people should not become mixed up and come to drinking animal blood. In his opinion, the Leather Carp should be prohibited despite being halachically permitted, simply because the Torah prohibits eating a fish without scales and fins.

Rabbi Ben David notes that he asked Rav Elyashiv about genetic changes and scaleless carp species. Rav Elyashiv told him that while halachically permitted, growing and selling scaleless carp is forbidden.

Part Kosher — Part Un-Kosher

The Gemara (Niddah 50b) notes that the male Tranegol Deagmo (commonly known today as the Hoopoe) is not kosher, while the female – is. The Tosefos explains this statement in two different ways. One sees both male and female as belonging to the same species, but while the male is a predator, the female is not. However, according to the second explanation of Tosafos there is no such possibility in the world, and if a species is kosher, both sexes are kosher or unkosher. Even though their names are similar these two fish are two different species and not the male and female of one species.

The Achronim explain that the two interpretations of Tosafos depend on whether the kosher signs  to determine if a fish is kosher mentioned in the Torah are indicators or causes. If they are indicators, having one sex kosher and the other unkosher is impossible; but if they are the reason — it is possible for one sex to be kosher while the other — not.

Despite the above dispute, there seems to be a halachic difference between fish and fowl.

The Tosefos add that since the Torah listed the 24 species of unkosher fowl, if the hoopoe does not appear on the list, it cannot be one of the unkosher ones, and only if it lacks all four signs of a kosher bird can it be deemed unkosher.


Despite being an unkosher marine animal, eels appear to have microscopic scales, visible through a magnifying glass. The Binyan Av (volume II, chapter 42) discusses the Kinneret eels which can reach giant sizes in which the scales are quite visible, as well as genetically mutilated scaled eels.

The Gemara (Avoda Zara 39a) recounts that fish called tzlofta was presented to Rav Ashi for ruling on its kosher status. The fish was examined in the sun and found to have scales. Rav Ashi deemed it kosher. Rashi and the Rishonim understand that the fish in question was the tzlofach, known today as eel, which is unkosher, but the one presented to Rav Ashi was of a similar species, which Rav Ashi deemed kosher.

In his conclusion, Binyan Av determines that all tzlofach – eel – are unkosher, whether or not they have scales. This prohibition is in place so consumers should not mix up kosher and unkosher variations of the same species.

Crossbreeding Fish

Since fish reproduce differently from mammals, the Rishonim maintain that the prohibition of kilayim does not apply to fish. Rabbi Yeshayahu Weiner (Chazon Yishayahu, 5753, 181-191) presented this question to a number of contemporary poskim in light of current scientific understanding of marine reproduction. Rabbi Moshe Sternbach permitted it since the crossbreeding as done by mammals does not apply to fish since the male and female do not interact, but Rav Elyashiv, Rav Sheinberg, Rav Fischer, and Rav Chaim Kaniyevsky forbade  using the sperm of one species to fertilize the egg s of another species.


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