Ari Enkin

“ The Rashba writes that only regarding blood, do we say that salting has no effect on vessels to bring it up, however in the case of the fish it would be forbidden. The Rashal holds that even for biblically prohibited items, salt has no effect to bring out the taste.
(8) It seems that they should be forbidden as the Mechaber holds that regarding fish we do not say that while they release their blood, they will release other blood for four reasons: a) Fish are a permitted entity and once absorbed with blood, become forbidden. ”

“ Even with regards to meat that had already expelled all its blood and tzir, we say that a second salting will cause the blood presently absorbed to be released. The first “there are those who permit” is referring to a case of meat that wasn't salted at all. The “those who forbid” at the beginning rule that salt can only expel its own blood but not blood absorbed from something else. ”

“ The reason is because kosher meat that was salted with non-kosher meat will easily absorb tzir even thought it won’t absorb blood since it is in the process of expelling its own blood. While meat is being salted to remove its blood, it can not absorb any other blood but it can absorb other liquids. Non-kosher tzir is biblically forbidden, but tzir from non-kosher fish, or tzir of meat that is forbidden because of blood is of rabbinical origin. ”