Something Fishy About Anisakis?

The current halachic rage – the status of fish known to host worms – presents two layers of fascination to me. From the very beginning, I recognized that how you generally understand the intersection between Chazal and science should determine how you approach Chulin 67B in light of scientific findings about the life cycle of the anisakis parasite. I thought that it would produce a rematch of the sides that squared off against each other regarding Rabbi Slifkin’s books. It didn’t. People weighed in on the fish in ways that seemed completely inconsistent with their expressed views on Chazal and science. (In many cases, this was because they simply had not gone through the gemara in any great depth.)

Additionally, there is an issue of loyalty. I have been a happy, contented mispallel at Rabbi Gershon Bess’ shlit”a, shul for over two decades. Rabbi Bess has been leading the charge against anisakis, and I therefore got drawn into the sugya.

When Rabbi Gil Student posted the latest from the OU , I tried responding on the Daf HaKashrus website, only to discover that the issue hasn’t been posted for the general public yet. I therefore am casting my net in a different place. I don’t think we’ve done halacha in Cross-Currents before; it really isn’t set up for serious halachic discourse. Then again, my comment on the Daf HaKashrus article doesn’t argue halacha so much as urge people (see the last paragraph) to learn more about the issue, so that their diets will be consistent with their hashkafa. Here is my comment:

The anisakis issue goes beyond the question of wholesale transgression of an issur d’orayso of sheretz hamayim, as if that is not severe enough. It penetrates to the heart of the our attitudes towards the relationship between Torah and science, and whether we regard the halachic system as having any integrity. People eager to employ koach dehetera might find themselves surprised when they learn about the conceptual basis for spearing that next forkful of fish.

You can approach anisakis in one of three ways.

1) You can argue (as many of the Chassidishe do) that worms form in the flesh through spontaneous generation. This is the basis of the Gemara in Chulin 67B permitting darni de-kavri, just as the gemara earlier had permitted kukyani at one point because minei gavli- they are formed from the flesh of the fish. Arguments by scientists denying such generation should be ignored, because science must bow to the mesorah of Chazal, who clearly accepted spontaneous generation. Furthermore, there is no reason to take issue with the clear statement of the gemara (which actually does not exist, and begins with Shulchan Aruch) that all worms found in fish flesh are kosher because they are products of the flesh. Therefore, there is no reason to get alarmed about anisakis any more than issues reported decades ago regarding other fish parasites.

2) You can argue that spontaneous generation must be rejected on the basis of voluminous evidence for what we know of reproduction. Nonetheless, halacha is determined by what Chazal said, regardless of whether they were “factually” right or wrong. The Ratzon HaBorei is that we follow Chazal, lehakel u-lehachmir, according to the information available to them in their day. (See the hakdamah of Sefer Dor Revi’i to Chulin, pgs. 7-8 in the most recent edition.)

3) You can argue that our task is to understand what principles Chazal were laying down based on their mindset. We then apply those principles based on our current understanding of the metziyus.

It is inconceivable that the OU would follow the first approach. Moreover, as recognized by Rabbi Belsky, shlit”a, himself, the gemara does not categorically rule that all worms found in fish flesh are permitted, period. It is easy to demonstrate that the gemara itself considered the possibility of worms that entered the alimentary canal of the fish, and found their way from there into the flesh by burrowing. The gemara only rejects this because worms would then be found in the gut, and were not in the fish considered by the gemara. The sardines in question have worms in their gut.

The second approach could conceivably be used, except that the gemara, as noted, does not categorically state that all worms found in flesh are permissible! Had the gemara stated that all worms found in the flesh of fish are permissible, without equivocation and without further analysis, it could be possible to use the Dor Revi’i’s approach, and permit them today. We would treat them similar to the way we treat killing lice on Shabbos, using the Dor Revi’i’s own example. The Pachad Yitzchok to the contrary, once the gemara permitted killing them (because it assumed that they generated spontaneously), they remain permissible to kill.

The gemara, however, does not say this. Again, as stated above, the gemara eliminates other possibilities of the provenance of the worms, and attributes it to spontaneous generation only when it is satisfied that they did not enter the fish through the digestive tract or some other orfice. Our observation of the life cycle of the anisakis parasite, our knowledge of how they enter the fish, encyst themselves in the stomach linings, and eventually burrow through to the flesh, would lead us to the conclusion that they are forbidden.

The third approach would seem most attractive, and is the one that Rabbi Belsky had been using till now. The gemara’s statement about worms coming from the flesh is taken as a principle that organisms whose entire (or majority) macroscopic development takes place within the flesh of a host can be considered halachically as part of the host, rather than halachically significant entities. Rabbi Belsky clearly declared this in a shiur a few years ago found on the OU website. By reasoning that I struggle to understand, Rabbi Belsky nonetheless argued that evidence that anisakis develops significantly outside the host fish before it is swallowed could be ignored. We are free to assume, as poskim have for centuries regarding the worms that they found, that the development of the worm takes place within the flesh of the fish, and is therefore still permissible. It looks like he is combining the first approach with the third, or shuttling between them. I can’t say I get it.

So what are these worms doing in the gut of the sardines? One would have to argue that they burrow out of the flesh where they originate and into the gut! Since we are confident, says Rabbi Belsky, that the worms are the kind that Shulchan Aruch permits, if we can be sure that the ones in the gut are of the same kind as the permissible flesh-worms, they too will be permitted. For this he turned to the scientists at the American museum, all of whom would be horrified by the pathway he describes. Nonetheless, since their DNA analysis shows that the gut-worms are the same as the flesh-worms, they are all mutar according to Rabbi Belsky, even thought those same scientists would all declare that they are the same because they travel from gut to flesh, not the other way around.

Rabbi Belsky in his response regarding the Anisakis clearly acknowledges that the worm originates from the outside. If so, how can he now claim that the path is from flesh to gut? Does it enter the gut, travel to the flesh – as he himself writes- then travel back into the gut? Even more troublesome is the fact that in the sardines the worms are found predominantly in the gut and to a much lesser extent in the flesh. I just can’t wrap my head around this.

For readers as confused as I am, I could not recommend too highly reading Rabbi Bleich’s magisterial treatment of the issue in the current issue of Tradition. He, too, cites DNA evidence – published evidence. His conclusion is reassuring as to the integrity of halachic analysis, although he does prohibit eating anisakis-infested fish.
Foregoing eating such fish seems to me to be a small price to pay for halachic consistency. For those less interested in halachic principle, let me reassure them that the impact on one’s diet is minimal. The vast majority of the fish we are used to eating are not problematic. The people most impacted are owners of fish companies that primarily sell the afflicted varieties. Most of us, it can be said, don’t have a horse-fish in this race.

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22 Responses

  1. joel rich says:

    The third approach would seem most attractive, and is the one that Rabbi Belsky had been using till now. The gemara’s statement about worms coming from the flesh is taken as a principle that organisms whose entire (or majority) macroscopic development takes place within the flesh of a host can be considered halachically as part of the host, rather than halachically significant entities. =======================================
    I agree that R’ Belsky’s (and R’Bleich’s) approach is intellectually consistent. I’m curious what you think the odds are that the principle articulated is actually what chazal had in mind (given the inability of the science of the times to use microscopes etc.)

    • Yitzchok Adlerstein says:

      I think that the odds are about 100% that Chazal had in mind that worms that originate in the flesh of fish are permissible. I also believe that they thought that the manner in which they originate in the flesh is through spontaneous generation. That, however, is irrelevant to the principle. The principle is similar to the kula that the Torah provides for drinking water with organisms that originate in the water without having left it, or eating fruit with insects that never emerged to the external world.

  2. micha says:

    Perhaps this “getting in the mind” thing should be something we try for with respect to today’s poseqim as well before publicly voicing astonishment.

    3b- We can argue, as Rav Dovid Lifshitz did in shiur with respect to maggots found within meat, that anything microscopic has no halachic “mamashus” (substance). Our water doesn’t have to be filtered to remove all the microscopic mites. Similarly microscopic bug eggs have no halachic weight. Therefore, the only cause the halakhah can be concerned with is the meat the maggot ate that got it from microscopic size to prohibited size. And therefore the maggots, or anisakis, are “caused by” the meat. Whether the microscopic worm was hatched in the fish or later swallowed by it, the distinction is irrelevant to this line of reasoning.

    The Daf HaKashrus has been available on-line (a href=>link), but I believe R’ Gil Student quoted R’ Belsky in full.

    The presence of nematodes (the general class of worm) in fish was known since the Egyptians (Ebers papyrus, c. 1550 BCE) and was studied by the Greeks and by Galen. They have infested the fish in the Mediterranean for millennia. Meaning, this was an issue in the Middle East back in the days of the Mishnah and Talmuds. And while the anisakis has a complex life-cyle, it isn’t unique — nematodes can be split in those with direct vs complex lifecycles. The anisakis itself was fully described in the 18 century by Carl Linneas.

    So, this is a new stringency in an old situation, one that we have no reason to believe our predecessors were ignorant of. This is R’ Belsky’s opening line, in only slight paraphrase — the gemara permits fish containing nematodes including this one. If you want halachic consistency, why not look for continuity over time rather than unifying over the most stringent common denominator?

    • Yitzchok Adlerstein says:

      People really ought to read the material before commenting. The issue of the non-significance of sub-visual phenomena is dealt with extensively in Rabbi Bleich’s article. Nothing new here.

      It is also quite besides the point. Rabbi Belsky does not dispute the metziyus, which is that the anisakis are macroscopic and free-swimming before they are ingested. He still thinks that they are OK. That was not the point of my article. My point was to question the consistency of using a type 3 approach, which is what he does, and still permit the sardines with worms in the gut. Even some of the Chassidishe who permitted other fish balked at this. Type 3 approaches do NOT take the gemara as stating that “all worms found in fish are mutar.” They see the gemara as permitting ONLY worms whose macroscopic growth has taken place entirely (or even to its largest extent, according to Rav Belsky’s reading) within the flesh, but not outside it. Arguing that the sardines are OK even though the worms are found in the gut – the very litmus test of external ingestion according to the gemara in front of us – seems to be quite a stretch.

      This is not a “chumra.” Reading it as a chumra means ignoring the pshat of the gemara. Consistency over time cannot ignore changes in the behavior of the organism – changes for which there are scientific explanation. Again, read the article.

  3. Chareidi Leumi says:

    >Foregoing eating such fish seems to me to be a small price to pay for halachic consistency.

    I can not agree. To me the price of dropping appoach 2 of the CI and adopting approach 3 leads to necessary radical changes to halacha. Mainly in the halachot of treifos where many (most?) of the treifos that chazal had are conditions with which we know the animal can easily live out the year – and where there exist many many conditions which are not treifos but are clearly lethal to the animal within months. And this is only one example out of many.

    • Yitzchok Adlerstein says:

      As I said within, a type 2 approach does not really work in this gemara. Had it said, “All worms in fish are OK,” you might be right. A type 2 approach (which you attribute to the Chazon Ish rather than the Dor Revi’i, with some justification) would then say that even if the gemara were predicated upon an understanding that all worms generate spontaneously, the halacha would not change. The 18 tereifos remain the 18 tereifos even if they now can live. But our gemara does not say that all worms are OK. It says that those found in internal organs (i.e. not in the alimentary canal) are forbidden, because we cannot exclude the possibility that they entered externally! It says that those in the flesh are OK because it is clear that they did not enter through ingestion, because then they would be found in the gut as well. – just as they are in the sardines. Nobody is “dropping” a type 2 approach here. Rav Belsky himself doesn’t use it. Invoking it is irrelevant to my point.

      It might be a good idea to keep in mind that pointing to tereifos as a firm basis for a type 2 approach is fraught. While it works in the Rambam, the Rashba resisted it. The Dor Revi’i himself notes this.

  4. Natan Slifkin says:

    The problem with the approach you describe is that the Gemara did not permit certain worms on the grounds that their “entire (or majority) macroscopic development takes place within the flesh of a host.” The Gemara’s reason was that they spontaneously generate. It’s true that it does not categorically state that all worms found in flesh are permissible, but it does state that certain such worms are permissible, for this reason. Whereas if you follow the approach that when we know that they originated outside, then they are prohibited, the end result is that the Gemara’s heter *never* applies and you have effectively undermined the halachic authority of the Gemara. You are also effectively claiming that Jews who ate Anisakis worms for thousands of years were all doing wrong.

    That’s why the Dor Revi’i’s approach – that we follow Chazal, regardless of scientific error – has to be used. This was also the approach of Rav Herzog.

    Regrettably, I cannot agree with your description of Rav Bleich’s impressive article as “magisterial” and certainly not “reassuring as to the integrity of halachic analysis.” Despite the great length of his article, he did not even acknowledge the existence of the approach of the Dor Revii and Rav Herzog, and furthermore he hedged on Chazal’s belief in spontaneous generation. I wrote a post about this that can be read at

  5. Doron Beckerman says:

    Does it enter the gut, travel to the flesh – as he himself writes- then travel back into the gut?

    According to Rav Belsky, yes. The Beis Yosef writes that all worms found in the gut are only forbidden because they may come from the outside. Worms found in the flesh are permitted, and they may have indeed migrated from there to the gut, and would still be permitted in theory.

    Rav Belsky is unwilling to wipe an entire halachah in Gemara and Shulchan Aruch off the books, and if one accepts the theory of anisakis worms as prohibiting them, then there is simply no such thing as דרני דכוורי. He claims that Rav Moshe Feinstein was presented with solid evidence of worms in cod originating from outside the fish, and nevertheless said that there was nothing to discuss – they are דרני דכוורי and permitted.

    • Yitzchok Adlerstein says:

      I am not sure which Beis Yosef you mean. I see the Pri Megadim who says that those found in the gut are only assur misafek. Certainly he means that they did not have to originate externally to the fish, but may have generated spontaneously within the walls of the gut, just as others generate within the flesh of the muscle. There is no evidence or assumption of worms migrating back out to the gut.

      Rejecting Rav Belsky’s approach (as do the gedolei poskim in Israel) does not mean rejecting the gemara. In my mind, it means accepting it, rather than bending it out of shape.
      It is clear in the gemara that if it were to find worms in the gut, it would assume that they were (betoras vadai or safek) swallowed. The heter of the gemara will still apply to parasites swallowed at a much earlier stage. T

      I am reluctant to accept anecdotal evidence of Rav Moshe zatzal’s positions without much confirmation.

  6. Tal Benschar says:

    While I have not researched every angle of the issue, one thing which jumped out at me when I first saw this is the issue of microscopic organisms — which to a great extent resolves the “Torah v. Science” issue.

    1. It is universally accepted that microscopic organisms have no halakhic status. Where it otherwise, then every cup of water would be teeming with shrotzim, and one would have to say that for millenia Jews have been ingesting shrotzim by the thousands with every drink. Someone mentioned on another blog that the Arukh ha Shulkhan originated this argument. I have not been able to track it down, but I also heard that R. Moshe Feinstein and R. Shlomo Zalman Auerbach held of it.

    2. The halakha of shrotzim is unique. The possuk says you need a sheretz ha shoretz ba mayim. The gemara understands this to mean that EACH INDIVIDUAL SHERETZ must have swam before it is assur. A sheretz that was born in the flesh of the fish and never swam in the water is not ossur. (A similar understanding is for sheretz ha shoretz al ha aretz.

    It is critical to keep in mind this deoraysa law. Usually the Torah uses descriptions of kosher/no-kosher animals to identify a species. (E.g. split hooves and chewing the cud). In this case, in contrast, you can have two worms of the same species, one kosher, the other not, depending on whether that worm ever swam in the water (or crawled on the earth).

    3. My understanding of the facts are that the fish swallows a microscopic egg or worm, which then burrows into its flesh, and then grows the point of visibility or even larger. Without a microscope, it would seem to spontaneously generate.

    But even though we now understand that the fish swallowed a swimming worm, at the time it was microscopic and hence had no halakhic significance. By the time the worm was visible to the naked eye, it was burrowed in the flesh of the fish. Hence there was never a time when it was both visible and swimming in the water. Accordingly, it was never a sheretz ha shoretz ba mayim.

    IOW, halakha simply discounts microscopic animals as having no significance. Someone told me that R. S.Z. Auerbach agreed with this argument.

    (Some consider this line of argument to be apologetics, but IMHO, it is an elegant way of dealing with the issue of spontaneous generation.)

    4. Someone also told me that R. Elyashiv disagrees in part. While he agrees that microscopic animals have no halakhic significance, once they grow to visibility, they are forbidden, even based on their history of swimming while microscopic. I personally have a hard time understanding that.

    5. In line with what R. Adlerstein relates here, there seems to also be a dispute as to the facts, i.e. whether the worms under discussion ever in fact are visible and swimming at the same time. IOW, some seem to claim that the fish swallows a visible, swimming worm, which later burrows into the flesh and grows. Others dispute this point.

    • Yitzchok Adlerstein says:

      I will reply only to item 5. All other points are discussed fully in Rabbi Bleich’s article.

      So is number 5, but I will briefly relate what he writes about this point (see note 64), which was raised by other readers as well.

      I don’t think that there is much of a dispute. There is quite a literature about anisakis. The smallest ones measured range from 144 to 215 microns. Generally they are between 281 and 293 microns long. The famed R Moshe Viya reports that opthamologic researches report that a person with normal vision can see an object five microns long at a distance of 25 centimeters.

      These critters don’t sound subvisual to me!

  7. David says:

    Rav Adlerstein:

    What is meant by “visible”?

    Isn’t it contextual?

    Would you say that tiny, translucent (or semi-translucent) anisakis is visible to the human eye in its natural environment, the open sea?

    I would guess not.

    • Yitzchok Adlerstein says:

      I’m going to leave that one for greater minds then mine. I hear your objection, but I can’t buy into using “natural” conditions. Tens of thousands of varieties of critters live their live at depths that no human could see anything. Do they not count? I would imagine that many of the shaylos in hilchos tola’im over the centuries dealt with organisms that spawned at the bottom of wells and cisterns with no illumination. What yardstick of size did they use?

  8. David says:

    For context to my above comment, 300 microns = about 1/100 of an inch.
    Furthermore, anisakis is 15-20 microns wide, the width of a thread.

    ALthough such a creature may indeed be visible to the naked eye given the right contrast, as per the opthamologist, I highly doubt it would be visible in its natural environment.

  9. David says:

    Rav Adlerstein,

    Perhaps you could pose the question to Rabbi Bess, given his deep involvement in this issue.

    Does it not seem necessary to define “nereh l’ayin” for the purposes of this halacha?

    When speaking of a semi-translucent, hair-thin creature, 100th of an inch long, is the standard a light box? A microscope? Naked eye + optimal lighting + optimal contrast?

  10. David says:

    So, were you able to fond out from Rabbi Bess what standard he uses for “nereh l’ayin”?

    Curious minds would like to know, given that as I noted on July 4, we are talking about a thread-thin, 1/100 inch long, translucent creature in the open sea.

    Once again, please clarify with him whether the standard is not its natural environment, but optimal non-natural conditions like with a bright light and black contrast.

    • Yitzchok Adlerstein says:

      We are getting there, at least piecemeal. Rabbi Bess notes that the most celebrated “bug” expert, Rav Vayeh, holds that the way to check whether an organism is considered subvisual is to hold it against a contrasting background. If it can be seen, we deal with it halachically.

  11. David says:

    To simplify:
    Isn’t there a difference between using the optimal light and optimal contrast in order to identify something that we have seen with our naked eye but cannot identify vs using it to see something that is otherwise not visible (thread-thin, translucent anisakis)?

    Reminder: The stage we care about, according to halacha, is where anisakis is free-swimming, not its size later on, after it it has developed within the fish.

    Is this not correct?

    • Yitzchok Adlerstein says:

      Apparently, there are important baalei halacha that think it not correct.

      As far as the reminder is concerned, R Elyashiv definitely disagrees. He is not alone. There is a section on this in Rabbi Bleich’s article.

  12. David says:

    Rabbi Adlerstein:

    I would appreciate if you would share with us which “important ba’alei halacha” openly extend the definition of “nereh l’ayin” to things we would otherwise not be aware of, were it not for having placed them under optimal light plus contrast.

    As I said before, there is a big difference between using the light/contrast to identify something vs using it to see something that is otherwise not visible. Has anyone explicitly rejected this distinction?

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