The Prohibition of Cooking and Eating Fish and Meat Together 

  1. Chazal had a tradition that it was forbidden to eat meat and fish that were cooked or roasted together. This prohibition applies to all fish and all meats, including fowl. If fluid from a fish falls into fluid from meat or fluid from meat falls into fluid of fish, the mixture is forbidden. 
  2. If meat and fish are roasted together without touching, so that only the smell of one combined with the other, the poskim disagree, but it is fitting to be machmir 
  3. Meat and fish that are salted together do not become forbidden but, lechatchilah, they should not be salted together. Whether or not meat and fish that were pickled together for 24 hours are forbidden is disputed by the poskim. 
  4. If meat and fish were in a basin, and boiling water was poured on them, they are not forbidden even though the boiling water cooked the surface of the meat and fish. The reason that the meat and fish are not forbidden is that Chazal did not forbid the combination of meat and fish in such a case and, besides that, there are some who hold that the danger of eating meat and fish together does not exist in these times.  
  5. If meat is cooked in a pot that was used to cook fish (even within the last 24 hours), or fish was cooked in a pot that was used to cook meat (even within the last 24 hours), the meat or fish is permitted. It is permitted to cook meat, wash the pot and then cook fish, and vice versa.  
  6. If while cooking fish, the fat of meat falls onto the outside of the pot, there are those who hold that the fish is forbidden, but it is fitting to be meikel 
  7. Breads and cakes that are baked in an oven that is used to roast meat may be eaten with fish. 
  8. If a piece of fish falls into a pot of meat while it is cooking and is removed immediately, the meat may be permitted because in so short a time the meat would not be forbidden.  
  9. Where there is a doubt whether fish fell into meat or vice versa, the doubtful mixture is forbidden, When something is forbidden because it is considered dangerous, we are machmir in cases of doubt. When it is doubtful whether the doubtful mixture occurred (sfayk sfayka), some are meikel and some are machmir 
  10. If fish fell into meat, and there are sixty parts of meat for every part of fish, the poskim disagree. Some hold that the mixture is allowed, others hold that the dangerous combination of foods is never allowed, no matter how much more meat than fish there is. In practice, modern poskim have permitted the meat. If the piece of fish can be identified, it must be removed and discarded. 
  11. When meat and fish are cooked together, is the pot prohibited and does it have to be kashered? The poskim disagree. Even though it is permitted to cook meat in a pot that was used to cook fish, when the meat and fish were cooked together, they formed a forbidden mixture. We are inclined to be machmir and forbid using the pot until it is kashered. There is also an important opinion that it is only necessary to allow the pot to stand for 24 hours.  
  12. After eating fish, a person who wants to eat meat should eat and drink something else according to the Rama. There is an opinion that he should wash his hands and eat pas sharui in order to clean out his mouth. This is the opinion of the Mechaber. If after eating fish a person touches his meat without washing his hands, the meat is not forbidden. We assume that there were at least 60 parts of meat against the very small quantity of fish that might have been transferred to it. 
MDhalachalMaase is written by HaRav HaGaon Rí Shammai Gross
Translated by Rabbi Tzvi Abraham