I don't know about Japan specifically but in the Caribbeans we'd often ship shrimps and other seafood in carbonic ice ("dry ice" in layman terms, turns solid be

I don't know about Japan specifically but in the Caribbeans we'd often ship shrimps and other seafood in carbonic ice ("dry ice" in layman terms, turns solid below −56.4 °C (−69.5 °F). It has the added benefit of leaving no residue. I noticed as a child that there's little to no smell when using this. Afaik (1990s), it's just more expensive (and possible frostbites without gloves iirc), so we don't use it when normal ice works, but I can see Japan using that for all wet markets (because sushi of all things).