I have only shipped within the country. But I have bought fish shipped from other countries. This include S. America, China and Indonesia. These fish usually arrive within 24 hours of being shipped. The key is to have all the needed clearances etc. in place as required. Always follow the rules for sending both our of the country of origina and the country or arrival.
I have had more domestic shipments go awry than anything coming in from overseas. But I also ship more boxes than I receive. The one thing I have learned is always to pack for there to be a delay, especially if needing to add heat or cold packs.
Also, it doesn't hurt to sacrifice a live chicken while you dance around the boxes before you ship. Yes, I am joking. Only kill the chicken if you plan to have it for dinner. The fish gods don't care if you eat it.