This case happened this past shabbos in my neighborhood and I wanted to hear the Rav’s view on the matter. A woman thought she was putting a tin foil wrapped piece of kishka in the chulent, but the kishka turned out to be gefilta fish. The chulent was on the smaller size, so there wasn’t even shishim presumably. However, can one rely on the Taz and others that say if the only issue is belios of fish (because the fish was wrapped well in tin foil) then we aren’t worried about danger, or do we say that we only rely on the taz in a classic nat bar nat case but here it is bevas achas all occuring at the same time?
As the question notes, the Taz (Yoreh De’ah 95:3) explains that the prohibition of eating a mixture of meat and fish applies only to eating actual meat and fish together. The taste of meat alone (ta’am), which is emitted by a pot or plate into fish, does not render it as forbidden food, and vice versa.
In this case, there is no actual mixture of meat and fish, but only the “taste” of the fish that goes through the foil, and into the meat. Therefore, it appears that no prohibition will apply.
It is true that in this case, the nat-bar-nat is besha’as bishul. According to some authorities, the transfer of nat-bar-nat “at the time of cooking itself” is more stringent than the general transfer of nat-bar-nat.This is ruled by the Chavas Daas (95:1), based on the Taz (92:24, quoting from the Issur Veheiter), and is also stated by the Chamudei Daniel (Basar Bechalav 44). The ruling is further implied by the Taz (95:2) and the Shach (97:2), the Be’er Yitzchak (9) and the Yad Yehudah (97:7) write that the question is a matter of doubt, and one should be stringent.
Yet, it is clear that a number of rishonim did not follow this chumra (see Yevakesh Torah, Basar Bechalav 16, anaf 2), and many later authorities are also lenient, such as Peri Megadim (M.Z. 2), Beis Efraim (YD 37), Peleisi (97:2), Yeshuas Yaakov, Beis Meir, Kanfei Yonah, and others.
For the issue of meat and fish, the harmful effects of which are not felt in our days, the tendency will be towards leniency, and this is especially true in the case of an entire pot of cholent — though one can be lenient even without substantial loss.
Very best of wishes as always!