(This should not be relied upon for practical halacha. When a question arises a Rabbi should be consulted.)
Does This Prohibition Still Apply Today-
1. The Magen Avraham (173) writes that there are many natural phenomena mentioned in the gemara that no longer apply today. The health concern of eating meat and fish is simply another example of something that used to be a real concern, but is no longer an issue. The teaching of the Magen Avraham is cited without comment by the Mishnah Berurah and the Aruch Hashulchan.
2. The Chasam Sofer (Y.D. 101) noted that the Rambam omits the concern of fish and meat entirely from his Mishnah Torah. The Chasam Sofer suggests that the Rambam knew that nature has changed and although there once was a legitimate health threat posed by mixing fish and meat, no such threat exists today. (It is important to note that the Chasam Sofer does not recommend that we rely on the Rambam’s opinion in this area.)
וכדאי לציין למה שראיתי בשו”ת מהרש”ם ח”ד ס’ קכ”ד וז”ל: “בדגים עם בשר שהמג”א צידד דליכא בזה”ז סכנה וגם אמרתי לרו”מ בשם ס’ הקנה דאחר אלף החמישי בטלה הסכנה אבל לא ראיתיו בעצמי רק ח”א אמר לי כן
3. The vast majority of poskim disagree and the basic halachah forbids eating meat and fish together. This is surely the universal custom and should be strictly adhered to. (The poskim do, however, take the Magen Avraham’s view into consideration and allow for some leniency in certain questionable situations, as we shall discuss later on in this chapter.)
Bitul B’shishim With Fish and Meat-
4. In general if an ounce of non kosher food becomes absorbed in sixty ounces of kosher food we assume that the entire mixture is kosher. We require sixty times the forbidden food to nullify it because the taste of the forbidden food is not discernible when mixed with sixty times its volume.
5. Although halachically forbidden foods may be nullified in sixty times their volume, the poskim dispute whether this principle applies to nullifying dangerous foods. The Taz (116:2), citing the Rama, rules that dangerous foods cannot become nullified in sixty times their volume. His ruling is based on the Talmudic dictum “chamira sakanta m’issura.” This means that something that involves a severe health risk is considered more stringent than regular prohibitions. In a case of a severe health risk, halachically there is no nullification, as halacha is extremely cautious when it comes to people’s health.
The Leket Yosher (Y.D. page 7) writes that his rebbi, the author of the Terumos Hadeshen, and the Maharam Mintz also ruled that dangerous foods do not become nullified in sixty times their volume.
6. However, most authorities maintain that even dangerous foods are nullified in sixty times their volume. The Shach argues that chamira sakanta m’issura is a principle that is limited to a case of doubt, but would not extend to the laws of bittul. Indeed, Harav Ovadia Yosef zt”l (Yabia Omer Y.D. 1:7) uses his encyclopedic knowledge of halacha to list all the authorities who rule leniently and he does so as well.
7. One very common practical application of the above dispute is the issue of Worcestershire sauce which is always made with fish. Many people enjoy eating their Worcestershire sauce together with meat. Some brands of Worcestershire sauce have sixty times the volume of other ingredients than fish, while others have a higher concentration of fish. The policy of the Orthodox Union Kashrut Division is to label any sauce that contains more than 1.67% fish with an OU Fish to indicate that it should not be eaten with meat. If, however, the sauce is composed of less than 1.67% fish they will not label it as containing fish indicating that it may be eaten with meat even though there is some fish in the ingredients. Harav Herschel Schacter shlit”a explains that the logic for this policy is that the Orthodox Union relies on the opinion of the Shach that foods prohibited on account of danger may be nullified. In addition, they take the Magen Avraham’s view (cited above) into consideration, that the danger of fish and meat no longer applies.
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