Freshness is all, and with the sushi fan's favourite fish, tuna, that means rapid progress from as far as the Pacific to a sushi bar in central London.
A typical journey for a yellow-fin tuna might begin off the coast of Chile. Landed at Lima in Peru, the fish would be flown to London's Heathrow. Within hours it is checked through customs and finds its way to Billingsgate fish market in London's Docklands. This can take three days, although the freshest tuna is used before it is five days old.
For Bay of Biscay fish caught by Spanish trawlers the turnaround time could be, exceptionally, as little as 12 hours.
Not that tuna eaten in Tokyo undergoes shorter journeys. It may have been caught off the West of Ireland.