The Kashrut of Herring, An In-Depth analysis

Hi, I was at a Kiddush and there was some discussion about whether herring contains worms. Could you please explain what this issue is about, and what HaRav Fried’s opinion is on the matter?

Thank you for your question.

The herring served at Kiddushim does raise concern about infestation. The type of worm found in herring is called Anisakis — a type of parasitic nematode commonly found in fish, including herring. While these worms are usually found in the internal organs, there have also been cases — especially in recent years — where Anisakis has been found inside the flesh of the fish as well.

I would like to share with you the Halachic discussion on the subject and then bring the Halacha by HaGaon Harav Amrom Fried Shelittah.

The chance of infestation is considered according to Halacha as מיעוט המצוי (mi’ut ha-matzuy), meaning there is a minority chance of finding it, but it definitely exists. For example, before we eat a date, we check it for worms, since even though most dates are not infested, we nevertheless check it, as it is something that exists and therefore should be checked

The same too, we could say that since there is a chance that there is an infestation of worms in the herring, the herring should therefore be checked before eating.

However, lehalacha, if checking for an issur that is a mi’ut ha-matzuy is very difficult or would ruin the food, then one does not need to check it before consumption (though each case needs to be analyzed individually). Regarding herring, it is a very difficult process to check for worms, since workers would need to inspect the fish under a special blue light—and even with the blue light, it is not certain that the fish is free of infestation, as the worms could be deep within the flesh of the fish.

Similarly, it would need to be clarified whether, lehalacha, there is an obligation to check for an issur that is a mi’ut ha-matzuy in a case where it can only be checked professionally.

Although we do find that even if checking requires professional expertise and takes a significant amount of time, we still perform the check—even in cases of mi’ut ha-matzuy.
For example:

1. We check the lungs and the gidin of the animal after shechitah, even though this raises the cost of the meat, since it must be professionally checked (although checking fish for worms would take even longer).
2. We also bring our new clothing to be checked for shaatnez by a professional

So according to this, one would also need to check herring for infestation, even though it takes time and requires professional inspection

(Although we could contemplate whether one who cannot detect the davar issur with the naked eye is obligated to use a blue light to identify it, this is brought in Shulchan Aruch Yoreh De’ah 98:4, where the Rema writes that since there is a way to identify the forbidden food, one is obligated to do so. Therefore, the same could be said in our case—that since there is a method, such as using a blue light, one should use it to identify the issur.)

One could also argue that this is a case of safek mi’ut ha-matzuy, since it is unclear whether the worms originated from within the fish itself (in which case they would be permitted) or came from outside the fish (in which case they would be forbidden). There is a dispute among the Acharonim—see Shu”t Beit Ephraim Yoreh De’ah siman 6 and Mishkenot Yaakov Yoreh De’ah siman 17—whether one needs to be concerned in such a case of safek mi’ut ha-matzuy.

Le’Halacha, HaGaon HaRav Fried shlit”a writes that it is almost certain the infestation comes from outside the fish, and therefore one should not rely on this leniency.

LeHalacha:
HaGaon HaRav Fried shlit”a writes in Azamrah Lishimcha, issue #293, that since the opinion of the Mishkenot Yaakov (Yoreh De’ah, Siman 17) holds that a 10% chance or higher is already considered significant, therefore, since there is a 10% chance of finding such worms, one must buy herring that has been checked. However, we do not rebuke those who are lenient.

This halacha also applies to other types of fish.

Cod fish (bacala): Spain and China
Young cod: Argentina
Zahavon: China
Lucet (hake): Argentina
Sole: China
Salmon: Canada, China, USA, and Alaska
Trout: USA
Cod: Norway and Iceland

Wishing you well.

Mishkenot Yaakov, Yoreh De’ah, Siman 17

Shulchan Aruch, Yoreh De’ah 98:4

Rema, ibid.

Shu”t Beit Ephraim, Yoreh De’ah, Siman 6

HaGaon HaRav Amram Fried shlit”a, Azamrah Lishimcha, Issue #293