According to both Rabbi Karp and others present, Rav Elyashiv stressed that the Anisakis is forbidden because of the clear evidence that it’s origin is clearly from outside of the flesh of the fish and are thus considered Sheretz HaMayim. Other worms that develop inside the flesh of the fish are permitted, however, and fall under the rubric of the Talmudic dispensation of “Minei Gavli” (See tractate Chullin 67b).It is difficult to consider a non-written teshuva, so I don't have much to work with here. And so I am stumbling about in the dark here. (Corrections are, of course, welcome.) There are good reasons for forbidding fish with the anisakis worm (though I still maintain they are permitted and we should not change our practice; and there is an alternate theory of the relevant halachot provided by Rabbi Belsky). What are these good, straightforward reasons? Namely, Chazal were operating under a theory of spontaneous generation -- minei gavlei -- and that is the only reason they would be permitted, along with the fish. But just as worms in the belly are forbidden, for they might have come from outside, so too any instance when they might have, or especially if they certainly came from outside. The scientific investigations conducted showed that the worms in the flesh came from the worms in the belly, and we know that the worms in the belly come from the outside.
Given a general statement of Chazal against eyewitness reports of the actual metzius, we would of course believe the actual metzius. This, in contrast to what Rabbi Chaim Scher wrote:
While we should embrace spontaneous generation, we should do so boldly and without apology. We trust the words of Chazal over what we can observe with our own eyes. This is a feat which only Hashem’s chosen nation, the Maaminim B’nei Maaminim, can accomplish. For, in the end, it is not scientists’ words which we disbelieve in favor of Chazal’s tradition, but rather evidence that our own eyes may confirm.But where there is no such concrete evidence, we are entitled to follow this general rule. (Of course, Rabbi Scher was talking about the general case, but explains why it does not apply in this present case.) Does Rav Elyashiv indeed believe that spontaneous generation operates on all these other fish, or even in general? He very well might. On the other hand, from Rabbi Scher again, Rav Elyashiv is willing to permit not just based on spontaneous generation but upon hatching of the eggs internal to the fish:
In truth, however, according to many Poskim including Rav Elyashiv and Rav Nissim Karelitz, a worm need not be spontaneously generated in order to be permitted. Any internal generation, even generation from an egg, would be permitted. Therefore, even worms that have been demonstrated to be generated from eggs may be permitted. It follows, therefore, that in order to prohibit these worms, it is not sufficient to prove that the worms generate from eggs; we must prove that they generate externally.This would appear to be in line with Rav Belsky's discussion of shoretz on the water; or alternatively, understanding minei gavlei as any internal development. I don't know whether this is to the exclusion of the possibility of spontaneous generation, or not. And that we rely on Chazal's statement as a general rule, but when we can directly observe the opposite, then this is NOT covered by the blanket heter of Chazal.
(According to Rabbi Scher's presentation, they would only be forbidden if is was
Rav Elyashiv is certainly entitled to his position, just as Rav Belsky is. I will explain my slight disagreements in a moment. But one important point I could extrapolate may be this:
If not for certain troublemakers who were looking to establish yet another thing as assur, who demonstrated to rabbis in a lab this migration from the belly, perhaps "we" would not "know" that they generate from the outside of the fish, and we could have continued to rely on the blanket heter of Chazal.
Perhaps not. Perhaps existing scientific discussion of this was sufficient. But see for example Rav Wosner:
Rav Wozner Shlit”a clearly stated in my presence and in the presence of Rav Shaul Klein Shlit”a, his Av Bais Din, that while in the past he did not feel an obligation to be Mocheh [protest] since the evidence was based only on scientific reports, now that there is a Raglaim L’Dovor [strong circumstantial evidence] that it enters the flesh from the viscera, one is obligated to protest.While I personally disagree with this distinction, based on an assumption that we cannot trust scientists, for they lie, it seems that this investigation by trouble-making busybodies was what sparked the recent issur.
Now here is my disagreement.
1) First and foremost, according to some reports, both Rav Vaye and Rav Belsky, who permit, were not allowed entry to speak to Rav Elyashiv about this. (There have also been denials on the point of Rav Vaye.) As such, he may not have been adequately presented with the reasons to be mattir, on the level of halacha or metzius. We have seen the tznius video where someone manipulated Rav Elyashiv to extract the answers he wanted. So while the halachic theory may be consistent and sound, I would not attach Rav Elyashiv's name and endorsement to it, despite firsthand reports that he does endorse it.
Call it instead the position of whatever Rabbis are propounding it.
2) This is based on a particular understanding of the relevant sources which I don't think is really true. Chazal and the Rishonim did rely on the idea of spontaneous generation. Substituting another theory and working with that in a way that we conclude that these in particular are forbidden does not convince me. Minei gavlei in almost all likelihood means spontaneous generation, and this was their basis. If you forbid these, first state categorically that spontaneous generation was the basis, and that Chazal were mistaken. And / or, then reevaluate ALL of halacha in ALL the places Chazal were incorrect in science. (This is true even here, where they are saying Chazal erred in science even as they claim they are not saying Chazal erred in science.) The osrim have no idea the major upheaval this would cause, and how many simanim in Shulchan Aruch would need to be rewritten. (That is, forbid, but accurately, and consistently! This, BTW, is the true reason I would say we should permit, though I should develop this in another post.) And if Chazal really meant internal generation of the eggs, or we could extend the reason to include internal generation from eggs, then regardless, Rav Belsky is correct that both Chazal and the Shulchan Aruch do not make distinctions but make a blanket heter. Yes, I know the difference, according to the present theory, is in how we may conduct ourselves, and whether we can rely on this assumption, where the metzius has changed -- the metzius that changed being our knowledge of the metzius. But the reason Chazal made this assumption was faulty science, and faulty observation. Why should we be able to rely on this blanket heter and assumption made by Chazal in error?
3) In terms of the science, it is not clear that these worms indeed generate externally. The eggs and larvae are swallowed by krill, the krill are swallowed by the salmon, and the anisakis then leaves the krill and enters the salmon. If swallowed when eggs, then perhaps this is enough "internally". If when larvae, perhaps not. (Why? Under a theory of shoretz upon the water.) On the other hand, as Rabbi Scher presents it, while earlier in the article he said:
It follows, therefore, that in order to prohibit these worms, it is not sufficient to prove that the worms generate from eggs; we must prove that they generate externally.But I think later he modifies this to the idea that they could have generated externally, according to "many" poskim. Emphasis mine:
There is broad agreement among the Poskim that the Gemara refers only to a case where there is no contrary evidence. Furthermore, many take the position that to prohibit a specific worm in fish flesh, we need not even provide definitive proof that the species is externally generated. Even evidence of doubt would be sufficient to question the assumption that a certain worm has internally generated. Where there is a reason to question the assumption, we will assume that the case is an exception. However, in absence of such evidence, we will assume that a worm is covered under the “blanket heter” of Shulchan Aruch.Who are these many poskim? Does it include Rav Elyashiv? If not, we have possible reason to permit.
4) There are other ways of permitting which I will discuss, even in light of all of this. And besides, Rav Belsky has a way of interpreting the sources to permit; because there are multiple ways of reading these sources and developing a theory of these halachot.
Note: Don't rely on this, or really anything on the Web, for halacha lemaaseh. Consult your local Orthodox rabbi instead.