> You're looking for something that goes bad in less than 1.5-two hours

I don't think the target is "goes bad" as much as "degrades in quality to a perceptible–or marketable–degree". Oysters, crab, et cetera (not sure about lobster) taste different, in New York, between the restaurants that make daily fish-market visits and those that skimp to three (or fewer) times a week.

And, yet, good sushi places in California get fish and shellfish flown in from Tokyo. Also, the tuna and some of the other fish sold in the Tokyo fish market is actually frozen.

To be fair, the practice of flying in fish from Tsukiji could easily be more related to prestige than quality. There are three major fish markets in Tokyo, and nobody cares about two of them (Kanda and Koto).

And who knows what the upcoming move of Tsukiji will bring :-)

So fresh sushi is less tasty than that made from frozed/aged fish.

The "fresh sushi" is more marketing than palate based - so say sushi/sashimi lovers.