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Parasites In Fish

by Rabbi Dovid Bistricer

© Copyright Orthodox Union 2010.
This article first appeared in THE Daf HaKashrus Vol 18 #8 TAMMUZ 5770 / JUNE 2010, a monthly newsletter for the OU Rabbinic Field Representative.
Reprinted with permission of the publisher.

FOR THE PAST several months there has been much public discussion about the presence of parasites found in the flesh of fish, with the OU’s position consistently lenient. On June 1, the OU hosted Rabbi Moshe Vaie, the world renowned expert in the field of hilchos tolaim and author of Bedikas Hamazon Ke’halacha. Rabbi Vaie, along with two other speakers, gave a thorough presentation about the current issue and its impact on the kosher fish industry. Also in attendance were kashrus professionals and representatives from the major kashrus agencies in the United States and Canada.

The current issue centers on the scientifically accepted lifecycle of the anisakis worm, a common parasite that is found in the flesh of fish. The anisakis is assumed in its immature form to originate in the ocean and undergoes a series of developmental stages until it finds its way into a fish, where it migrates from the stomach to the flesh. Although Chazal and the Shulchan Aruch unequivocally permit worms found and grown in the flesh of fish, halachically those found in the stomachs are considered forbidden since they are assumed to have been directly swallowed by the fish from the ocean. The scientifically accepted lifecycle of the anisakis seemingly describes a sheretz that is halachically forbidden, whereas Chazal and the Shulchan Aruch permit worms found in the fish’s flesh without qualification.

Rabbi Vaie began by discussing and presenting a slideshow about the prevalence of anisakis and similar parasites throughout the fish industry. Rabbi Vaie emphasized the following points:

  1. There are thousands of species of parasites that may be found in the flesh of fish that are commonly consumed.
  2. The presence of parasites in fish flesh is highly prevalent and in large volumes. It is therefore not possible to properly clean fish from these parasites, as only a modest percentage will be removed.
  3. Parasites in the flesh of fish is not a new phenomenon, but can be traced back 700 years ago in the literature of Rishonim, which also recognize that these worms are not dormant but can migrate.
  4. The size of the immature parasites while in the ocean is microscopic and therefore not forbidden at that stage. It is possible to suggest that since the microscopic parasite develops as noticeable in a host after it is ingested, it is therefore not considered a sheretz hayam.
  5. There are still several unknowns in the world of science regarding parasite development.
  6. This precise issue was presented years ago to numerous gedolei yisroel, many of whom ruled leniently.

Rabbi Vaie also summarized the current positions of certain gedolei yisroel in Eretz Yisroel:

  1. Rav Shmuel Wosner shlita and Rav Yosef Shalom Elyashiv shlita advise one to be vigilant.
  2. Rav Nissim Karelitz shlita has ruled that one may eat fish without checking for parasites, although if a parasite is noticed it should be removed.
  3. A well known and highly respected kashrus agency in Eretz Yisroel certifies herring; despite consistently high concentrations of anisakis. This is because their Beis Din essentially assumes that parasites found in the fish flesh are permissible.

Rabbi Moshe Yosef Blumenberg, an associate of the Tartikover Beis Din who has researched a significant amount of scientific data in this area also presented. Rabbi Blumenberg demonstrated the following points:

  1. Scientific studies assume that migration between the stomach and flesh occurs while the fish are still living, unlike what others have suggested that it occurs after death since the fish are not gutted properly.
  2. There are discrepancies and differences of opinion amongst scientists with details about the anisakis’ lifecycle.

The third and final presenter was Rabbi Yechezkel Meisels, mora de’asra of Ehel in Williamsburg. Rabbi Meisels related that he was present with Dayan Gross in 1978, when this same sheilah was presented to Rav Moshe Feinstein zt’l. Rabbi Meisels proceeded to tell the background of the sheilah prior to visiting Rav Moshe and that he received letters from two scientific experts outlining the lifecycle of a parasite that is found in the flesh of fish. Rabbi Meisels recounted how he and Dayan Gross came to Rav Moshe with samples of fish and these two letters, showing them while explaining that modern science assumes that these parasites originate from outside the fish. Nevertheless, Rav Moshe unwaveringly responded that since the parasite is found in the flesh of the fish, it should therefore be permitted in accordance with Shulchan Aruch. When asked if a teshuva could be written, Rav Moshe declined since the answer is clearly found in the Mechaber.

Throughout the meeting there was ample and extensive discussion of the differing sides of the issue.


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