I ship frozen salmon to a friend that lives in suburban Washington DC every fall. I foodsaver it, freeze it and ship it FedEx next day with frozen gel packs in the box. It always arrives in primo shape still frozen. I don't know if they are available where you live, but here I can buy sturdy cardboard boxes that have a one inch thick styrofoam liner made for shipping frozen product. The box will hold about 6 frozen silver salmon.
Just like Nick and Larry said.
Friends don't let friends eat farmed fish.
"People sleep peacefully in their beds at night only because rough men stand ready to visit violence on those who would do them harm."