Try this. Bag some up WITH NO SALT but use normal water supply and then bag some with NO SALT and USE BOTTLED WATER (go buy a couple of gallons for this test). Put a big X on the No salt and a check mark on the no salt, different water and them. Then un-thaw the fish and see if there's a difference.
Why in the world are you soaking them in saltwater anyway?
Yes if you let the tap water sit out for a few minutes the chlorine will be gone. Also human flesh soaks chlorine up so why not fish flesh? Test your water to see how much chlorine is in it.

