The following is an article written for Matzav.com by a talmid of Rav Yisroel Belsky shlit”a explaining Rav Belsky’s stance on the anisakis parasite in fish on a basic level. To view Rav Belsky’s full teshuvah, click here.
By Rabbi A. Margolin
The tzibbur has recently been flooded with literature pertaining to a recent tumult in reference to the presence of parasitic worms in fish. The following is a synopsis of several shiurim that Hagaon Harav Yisroel Belsky shlita, rosh yeshiva of Yeshiva Torah Vodaath and senior posek of the OU, has delivered on the inyan.
The Gemara in Maseches Chullin says that sheratzim in water that never separated from the vessel holding the water are permitted to be consumed. The reason for this is because the Torah excludes such a creature from being a sheretz hamayim and, until it gets separated from the water, it is not a sheretz ha’aretz. Similarly, worms that are in produce that were not there while the fruit was attached to the ground are permitted for consumption provided that the worms did not leave the produce. Once again, it is not considered to be a sheretz; it is obviously not a sheretz hamayim, it is not a sheretz ha’of, and, because it was never on the ground, it is not a sheretz ha’aretz.
In short, a sheretz has to be classified as either a sheretz hamayim or a sheretz ha’of or a sheretz ha’aretz to be assur. Otherwise, it is permitted to be eaten.
The issue that was recently raised concerns the anisakis parasite. In a nutshell, the parasite’s eggs are found in a large amphibious creature such as a whale, dolphin, or seal. The microscopic larvae pass out with the excreta and are then consumed by a host known as crustaceans (shrimp-like creatures). In their host, the worm grows and may sometimes become nireh la’ayin. The crustaceans are eaten by kosher fish and thus the parasites end up in the stomach of a kosher fish. As parasites, the anisakis worm may bore through the fish’s stomach and work their way into the flesh of the fish.
The Gemara, as interpreted by Tosafos, says that the worms that are found in the stomach of a fish are forbidden, but the worms found in the flesh of the fish are permitted. The Bais Yosef in Yoreh Deah (Siman 84) says that the reason the worms in the stomach are assur is because perhaps they came into the fish as fully developed worms and thus were included in the issur of sheretz hamayim. [The Pri Megadim paskens this way as well.] This is unlike the worms that entered the fish that did not have the status of sheretz hamayim. In other words, when one observes worms in the stomach, one does not know if they are mutar or assur. The Shulchan Aruch rules clearly that worms found in the flesh of fish are always permitted. It is possible that Chazal knew that worms that were sheretz hamayim would not enter the flesh of the fish.
In summary, worms in a fish’s stomach are assur misafek and worms in the flesh of fish are permitted.
In the case of the anisakis worm, the worm in its microscopic state is not considered a sheretz hamayim; any organism not visually discernible by the eye has no meaning in halacha. Thus, this worm was never exposed to the water and is not considered a sheretz hamayim. The fact that it was “hosted” by a crustacean does not have any negative halachic effect as far as yotzei min hatamei (see Chavos Daas, Siman 81:2). [Even those who disagree with the Chavos Daas would agree in this case, since "minei gavli," as will soon be explained.] We are not concerned that the worm was in the fish’s stomach prior to its migrating to the flesh and was thus considered assur; its assur status is only a safek, and once it is in the flesh, it is permitted.
Some claim that since the Gemara describes the worms that are in the flesh as “minei gavli, ” a worm is not permitted unless it can be ascertained that it was generated spontaneously by the flesh of the fish. This is because they define the word “gavli” as “being created.” However, since we became aware that all worms without exception come from outside sources, and there is no such thing as spontaneous generation in any shape or form, then, by extension, it is proven with complete certainty that the words “minei gavli” mean something else. Rashi, who says “lashon gadli,” defines the word gavli to mean “to grow.” This means that the worms in question entered the host in miniscule form and grew off their host. He gives no reference to the idea of spontaneous generation, a concept alien to Chazal and most certainly not required by halacha.
[Paranthetically, the common louse which Chazal describe as "eino parah v'rava," commonly translated as meaning that it does not reproduce, does very certainly reproduce. Furthermore, its eggs, commonly referred to as nits, are visible to the eye. Nevertheless, one is permitted to kill it on Shabbos because of its status. Rav Belsky explains that the louse can not survive on its own; its survival is dependent on mooching off the host's protein. In the case of a human, this is usually through the hair. Thus, we have another example how the words of Chazal have been misinterpreted.]
It is important to note that the Shulchan Aruch, when allowing consumption of worms in the flesh of fish, does not differentiate between worms; the heter is a blanket heter. Had there been a limitation on types of worms the, Shulchan Aruch would have indicated as much. This is especially true in light of the fact that the anisakis worm had already been identified in the time of the Mechaber. Futhermore, there is no way for a lay person without expensive equipment to determine which worm he is looking at - whether it is the anisakis or any other type of worm. If we were to forbid the anisakis, then we are forbidding all worms, contrary to the p’sak of the Shulchan Aruch!
In 1978, the Rashkebeha”g, Rav Moshe Feinstein zt”l, was asked about worms in the flesh of fish. He paskened, in accordance with the ruling of the Shulchan Aruch, that there was no concern.
One writer suggested that the p’sak of the Shulchan Aruch permitting the worms is limited to a specific parasite that enter the fish from the outside and is microscopic. This is simply absurd. Had the heter been limited to one type of worm, the Shulchan Aruch would have said so.
Another writer claims that a study in Norway found that the fish today are far more infested with anisakis worms in the flesh, because the fish lay packed together after they are dead and are therefore more prone to the parasites working their way into the flesh. This is in contrast to years ago when the fish would be cleaned immediately upon capture and there were very few worms in the flesh of the fish. Thus, it was a mi’ut sheaino matzui. This argument has no basis. The concept of miut sheaino matzui is in reference to when we have an issur, but we do not know how prevalent it is. When the likelihood is a low one, we do not need to consider it. Here, we are not talking about whether or not it is a rare occurrence. The point is whether or not worms in the flesh are assur or mutar, and the halacha is that they are mutar.
Others expressed concern that once we know that it is the same worm from the stomach that is migrating to the flesh and it is established that worms in the stomach are assur, how can those same worms subsequently become mutar in the flesh?
However, since the Bais Yosef explained that the issur is because it is a safek, there is no issue with them once they migrated to the flesh, as previously explained.
It is noteworthy to mention that a recently publicized letter which argues that anisakis should be assur is actually the most convincing proof that it is mutar. This is because all the reasonings stated therein to prove that the worms are assur would also apply equally to all other worms found in fish, rendering all worms in fish assur. However, this cannot be, since Chazal clearly state that they are all mutar. Thus, the only possible alternative, and consequently the truth, is to say that the reasoning is faulty and that they are all mutar. [The fault in the reasoning should be easily understood by anyone who read the forgoing material, but whether one discovered the flaw or not is immaterial, as no amount of reasoning in the world could lead to an absurd conclusion - that the p'sak of the Shulchan Aruch permitting worms is rendered obsolete.]
In conclusion, the p’sak of the Shulchan Aruch, permitting those worms found in the flesh of the fish, applies to the anisakis worm just as it applies to any other worm.