[mass55th]

"It was a large grey fish, now swimming in preservative instead of the ocean. "

They have never been able to keep one alive for long after being brought up in a net, and kept for study.

[EinNYC]

They have never been able to keep one alive for long after being brought up in a net, and kept for study.

That is because there is a large difference in water pressure where they live and the surface. They cannot live in the lower pressure water.