Shipping frozen fish to Michigan?

On 2 occasions, I have brought frozen salmon on international flight.
From the time I packed and unpacked was around 30 hours. Still frozen when the box opened.
One box weight about 40lb of frozen salmon.

I got Styrofoam box from walmart. Pack vacuum sealed salmon to the top of the box. No dry ice. Just frozen fish.
No one have asked anything where I got the fish from.