I don't know, but guess the cost of shipping fresh fish is $$$
One avenue that maybe worth looking at is filleting the fish, smoking it & packing it. Whilst it would still need to be chilled, you could pack to a greater density.
I have some contacts in the hotel and catering industries, I will have a chat and we may be interested ourselves subject to some research.
What amounts are you able to export freshly and whats the timescales to land in The UK?
Many thanks