Freezing fish can be a slippery slope, and there are opposing views on this subject. Fast freezing causes less damage to the flesh and this is why so many commercial processors use this method. Slower freezing can cause the cell tissue to burst.
One point of view for smoking fish that was frozen is that ruptured cells will take the flavors in the (dry or wet) brine easier, and take smoke easier. The opposing point of view is that ruptured cells will result in greater moisture loss during thawing -plus- the salt in the brine draws out moisture... so both of these things will result in a change in texture. I have smoked a lot of trout for friends that they had frozen and I can tell a difference in the moistness and texture. I actually field dress trout for smoking immediately after catching them, and get it on ice. This is especially true for river or lake shore trout. This reduces the effects of rigor, and trout are not a stringer fish.
Timing for your brine (wet or dry) depends on the brine strength, the species of fish, and the thickness of the fillets. I smoke 99% of my trout, steelhead or salmon with the skin-on so that is a factor as well.
Here is an article I have updated over the years that uses a dry brine method.
Revised 1-13-2022 Cured fish has been prepared for centuries as a means of food preservation. Because of refrigeration and our knowledge ...
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