Halakhah su Levitico 11:10

Creatures lacking fins and scales "of all that swarms in the waters" (Leviticus 11:10) are biblically proscribed. Included in the prohibition against consuming such marine creatures are not only fish and crustaceans but also insects and the like whose natural habitat are "the seas and the rivers." Such creatures are forbidden even after having been ingested by a kosher fish but, as explained by the Gemara, Hullin 67b,²⁰Actually, the Gemara discusses rules applying to animals but does not explicitly refer to fish. Tosafot, ad locum, state that the underlying principle applies equally to fish. similar organisms generated within an animal or the flesh of the fish are permitted. Accordingly, as recorded in Shulḥan Arukh, Yoreh De'ah 84:16, worms found within²¹R. Ephraim Zalman Margulies, Teshuvot Bet Efrayim,Yoreh De’ah, no. 25, writes that, even when found on the external surface of the entrails, such organisms are forbidden. See, infra, note 50 and accompanying text. the entrails²²As understood by Rashi and Tosafot, the Gemara, Ḥullin 67b, indicates that such creatures are also forbidden when found in the liver or lungs of the animal or of the fish on the suspicion that they entered through the “nostrils.” Ḥiddushei R. Akiva Eger, ad locum, adds the phrase “or in the brain” reflecting the possibility that the worms might have entered through the nose and penetrated the cranial cavity. of a fish are forbidden because it is to be presumed²³Pri Megadim, Siftei Da’at 84:43, indicates that such creatures are prohibited, not with certainty, but as a matter of doubt since their presence within the digestive organs strongly suggests that they originated outside the fish. This view was expressed much earlier by Issur ve-Hetter he-Arukh, sha’ar 41, sec. 15. The Gemara found no reason to assume that organisms found elsewhere within the fish originated outside the fish and hence, if found under the skin or in the flesh of the fish, they are permitted. The matter can best be categorized as an application of the principal “ka’an nimẓa ka’an ḥayah—what is found here was always here [and not elsewhere]” other than in situations in which there exists a rei’uta, or unusual factor, giving rise to suspicion of the contrary.
Consistent with that principle, Knesset ha-Gedolah, followed by Baḥ and Yam shel Shlomoh in his commentaries on Sefer ha-Terumot and on Ḥullin 3:104, concludes that worms are permitted only if found in a whole fish and upon examination it is ascertained that there is no lesion through which the worms might have entered. However, once the fish has been cut, any worms that are found are forbidden because of the fear that, in cutting the fish, they may have penetrated the flesh from the viscera. that they were earlier present in the water and were ingested by the fish, whereas such creatures, when found between the skin and flesh, or, according to most authorities,²⁴See, however, Baḥ, Yoreh De’ah 84, Knesset ha-Gedolah, Yoreh De’ah 84:101 and Yam shel Shlomoh, Ḥullin 3:106, who permit such creatures only when found between the skin and the flesh. See infra, note 25. within the flesh of the fish itself,²⁵Rashi identifies the “darni” explicitly permitted by the Gemara, Ḥullin 67b, as “worms found between the skin and the flesh.” Rashba, Torat ha-Bayit ha-Kaẓer, bayit slishi, sha’ar shlishi, adds the phrase “or in the flesh” and that emendation is incorporated by virtually all subsequent authorities. are permitted.²⁶Nevertheless, when detached or separated from the fish, such worms are forbidden because of ma’arit ayin, i.e., because they appear to be forbidden creatures. Contrary to other authorities, Shakh, Yoreh De’ah 84:46, permits such creatures as long as they remain in the plate in which they are served but forbids them once they leave the plate for another surface. Cf., Pri Ḥadash, Yoreh De’ah 84:9 and Ḥokhmat Adam 38:29. Even if they develop within the fish while the fish is still alive, such creatures are regarded as having originated in the fish itself.²⁷R. Hai Ga’on, She’iltot, Parashat Shemini, she’ilta 4, explains that, since such creatures are generated by the flesh of the fish or animal, they have the halakhic status of their progenitor.
It is generally presumed that the Gemara asserts that such creatures arise in the flesh of their host as a result of spontaneous generation. However, Rashi, Ḥullin 67b, defines the term “gavli” in the phrase mineih gavli as meaning “gadli,” i.e., “grow” or develop.” That understanding is entirely consistent with the notion that the parasites enter the flesh while yet microscopic in nature—and hence are accorded no halakhic cognizance—and later develop within the flesh. Since their existence is recognized only when they become visually perceivable within the flesh of the host, their halakhic identity is that of the host in which they “grow” or “develop.” See infra, note 57. As enunciated by the Gemara, the applicable principle is that creatures that grow from the flesh of a kosher fish or of an animal that has been slaughtered²⁸Only worms generated in the flesh of an animal after it has been slaughtered are permitted; a worm generated in the flesh while the animal is yet alive is forbidden as “an organ torn from a living creature.” Since the worm enjoys independent animation, it is not rendered permissible by the slaughter of its host. Fish do not require slaughter and are not subject to the prohibition against an organ torn from a living creature. Hence, worms generated by the flesh of a fish, even when the fish is yet alive, are permitted. are entirely permissible.

The almost reflexive reaction of many people to reports of infestation of New York water by copepods was that the issue is hardly novel. Probably every person who has had the benefit of a freshman biology course has had the experience of placing a droplet of water on a slide and examining it under a microscope. The experience of viewing countless numbers of microorganisms is both thrilling and disconcerting: Thrilling because the microscope becomes a window opening upon the hidden mysteries of divine creation through which a tiny cross-section of the myriad complexities of the natural order is revealed; disconcerting, at least to a Jew, because, mindful as he is of the biblical admonition "of all that creeps in the water and of all the living creatures that creep in the waters … you shall not eat of their flesh" (Leviticus 11:10-11), he becomes jarringly aware that with every sip of water he imbibes copious quantities of such creeping things.

Rabbi Efratti cites the commentary of Tiferet Yisra'el on Avodah Zarah 2:6, which declares that for a fish to be deemed kosher its scales must be visible to the naked eye. This ruling is based upon two considerations. First, the Gemara, Niddah 57b, identifies the biblical term kaskeset as the "clothing" of the fish and, accordingly, defines kaskeset as "scales." Microscopic scales can hardly be deemed "clothing," and hence cannot satisfy this necessary condition of kashrut. Secondly, Tiferet Yisra'el establishes the general principle that in all matters contingent upon vision, Halakhah is concerned only with what is visible to the naked eye, not with what is visible under a magnifying glass or microscope. Rabbi Yechiel Michel Epstein reiterates the same principle in his halakhic compendium, Arukh ha-Shulḥan, Yoreh De'ah 83:15.^10aCf. also, Arukh ha-Shulhan, Yoreh De‘ah 84:36. Arukh ha-Shulḥan adds that mere perception of the scales is in itself insufficient since it is necessary that scales not only be present but that they be removable as well. This qualification is indicated by Ramban (Commentary on the Bible, Lev., 11:10) in his definition of kaskeset as a structure "which can be peeled off as one peels a fruit or removes bark from a tree."