When we travel south each fall we have 150# of fish in our baggage. We also haul 100# fish back east to our daughter and family each summer. Then all of our house guests fly home with lots of fish. Yeah, we eat a whole lot of fish and know a lot of serious fish eaters!
And it all makes it safely and in fine condition. But, we're set up for doing it. Everything from vacuum sealers to cold freezers to scales and insulated shipping boxes.
And that's what it takes. If you're not set up for it, though, you kind of climb out on a limb quality-wise. If the fish thaws along the way, you're wasting your money and the fish. Hard to be set up too, when you're traveling.
The airlines are all set up with freezers at the major hubs, and if the boxes (insulated!) are labeled, they'll be put in freezers for a long layovers. In the Seattle airport there's a freezer service right across from the baggage claim if you are spending a day or two before continuing.
Yeah, you'll pay excess baggage for a box of fish. But if it arrives in good form, you're only paying around $25 for a 50# box of incredible fresh fish.