Based on a Naaleh.com shiur by Rabbi Michael Taubes
Rav Kana taught that if one bakes bread in an oven with roasted meat, one cannot eat this bread with dairy. Further on the Gemara in Pesachim writes that Rava B’Parziska prohibited consuming fish that had been roasted in an oven with meat, together with dairy. Mar B’rav Ashi adds that one should not even eat the fish itself because it causes bad breath and tzoraat.
The Shulchan Aruch develops this halacha further and writes that not only may one not eat fish roasted in an oven with meat, but one should refrain from eating fish and meat altogether. The Rema notes that b’dieved if one already cooked fish and meat together it is permitted. This is corroborated by the Shach. The Beer Sheva disagrees and rules that even b’dieved one may not eat it since this is a question of danger. The Chasam Sofer notes that the Rambam did not cite this din at all. He postulates that the case mentioned in Gemara may have referred to a particular fish, or that human nature has changed since ancient times and the danger referred to no longer exists. Nevertheless the Chasam Sofer rules that “Minhag avoseinu k’din“-the customs of our forefathers are like law and therefore we do not mix fish with meat. However we cannot say that the laws of meat and fish are stricter than the laws of meat and dairy.
The Shulchan Aruch writes further that one should wash ones hands and eat something to wash out ones mouth between fish and meat because it can lead to tzoraat, and “Sakanta chamura m’issura“-Matters of danger are more stringent than prohibitions. The Magen Avraham disagrees and notes that we find many examples in Gemara where Chazal tells us about dangers which are not found today. This is because our natures have changed and we dwell in different lands. Therefore there is room to be more lenient here. The Mishna Berura rules that we follow the Rema who holds that one does not need to wash ones hands between fish and meat. The Rema writes that fish and meat are only a problem when they are cooked together however it is still better to eat or drink something in between courses. The widespread practice in Klal Yisrael during the Shabbat meal is to drink liquor between fish and meat.
Chazal categorized poultry the same way as meat with regard to the laws of meat and dairy. Therefore the halacha would be the same in regard to fish and meat too. Some Sefardic Poskim prohibit consuming fish with dairy. Rav Akiva Eiger notes that there is a practice to refrain from drinking water after fish because that too is a danger. Indeed as noted, the custom is to drink schnapps. Perhaps the minhag to say L’chaim after drinking an alcoholic beverage stems from this idea.
Living a Torah life means living a measured, focused, existence. There is meaning and purpose behind everything we do. May our studying and knowing the halachot well help us reach our ultimate purpose.