From the words of the Mechaber it seems that we are referring to a case of fish that was not salted yet, and even so it is forbidden and salting it will not help, for with fish we don't say the rule that while it releases its own blood it will release other blood. They are soft and will absorb a lot that will not come out through salting. Not like the Rema who holds that we do say that the fish will release other blood that has been absorbed.
 From the words of the Mechaber it seems that even if they are touching they are permitted. This is difficult to understand for in the case of non-kosher meat that is not salty, touching kosher meat that is salty, the Mechaber brings the opinion that forbids them! The answer is that nevertheless, the non-salted one is not considered roseiach enough to release blood for here the only problem is because of blood that the poultry releases and may be absorbed in the fish. This is not the case over there where it releases non-kosher tzir which is forbidden.
 This is only if we are certain that the fish did not fail to the bottom, if we do not know this for sure it is forbidden, for it is common during salting that items on top fall to the bottom.
 The same is true in a case where they were placed on the same side, that if the fish Is higher than the meat what is above is permitted and what is beside it is forbidden. Even what is on top is forbidden to the extent of a klipah.
 Nevertheless one must remove a klipah. The reason that this was left out is because the Mechaber holds that all problems through salting require a klipah, whereas the Rema wrote this law for us who forbid the fish unless there is sixty. However when placed on the poultry it is permitted with only a klipah being removed.
 Even though it says later on in section 91, that even after the required salting time it is still considered roseiach, the case over there is dealing with meat and cheese. This is not the case here where we are dealing with the prohibition of blood, which is non-existent after the required salting time. In the case of Rashi in section 69 where we forbid the meat even after the required salting time, is also a different case for over there the meat is sitting in tzir, which is not the case over here.
 This is even if the fish sat as well since the beginning of the required salting period, that they are permitted. They should not be declared forbidden because of tzir coming from the poultry unless they were placed in the tzir.
 This is only post facto. Initially one is forbidden to salt fish in a vessel used for salting meat, for in any event they must be washed and we are worried that it will be forgotten. This is referring to fish salted in order to be cooked immediately in which it is not common to wash them off. However, with fish being salted for preservation in which it is common to wash off before cooking, it is permitted even initially to salt them in a vessel used for salting meat. See later on in section 91 where we say that if the vessel was wiped well one need not wash them.
 The Rema is explaining his own opinion, however according to the Mechaber it is not so for he does not hold that by fish we say that as it releases its own blood, it releases other blood.
 Not necessarily simply washed, for even if washed, the fish are forbidden because even though the pores do not close up, the fish releases all it’s tzir before the poultry releases it’s blood. The word “washed” over here, is defining that meat washed off of its salt and is considered saltless.
 It is explained over there in section 5 in the Rema, that tzir from salted meat, even if only salted for the purpose of roasting, is considered roseiach, and this is indeed the law. The Issur V’heter writes that one should not forbid fish salted with poultry for there is no danger through salting. This is referring to a case where there are no problems of blood as when salting for preservation, however when blood is involved it is forbidden.