Li Du did not know how so many fish ended up frozen in one ice sheet. Most of them were deep-sea fish, and it didn't seem plausible that a single wave of frost did away with them all.
Blue-fin tuna, in particular, was a fish that commonly lived in very cold climates but rarely froze because it was in motion all its life.
That fish used percussive breathing to stay alive, which meant that it constantly swam, letting water through its gills and then absorbing oxygen as it passed through. They never stopped moving, so they wouldn't freeze unless the ice traveled very abruptly.
The polar regions were the places where most of nature's mysteries were buried. Li Du stopped thinking about it because he didn't understand it. The space-time bug flew into the ice and when he found the blue-fin tuna, he started work.
Seven or eight meters long and four or five meters wide, the fish was a colossal mass, and it was not easy to carry it back.