Wouldn't these deep-sea creatures die?

They wouldn’t have the same problem that a human would have breathing ‘air’. The problem with ‘air’ is the all of the nitrogen in it that doesn’t dissolve in our blood. Breathing air at sea level (or a little above or below that pressure) is okay for humans, but if you breathe compressed air at very high pressure, then you also have high pressure undissolved nitrogen in your blood. That’s okay as long as you stay at the high pressure, but if you rise quickly, then the nitrogen gas expands too quickly, hence ‘the bends’.

Sea creatures who live their whole lives at high pressure obviously don’t breathe air, so they don’t have that problem.

Apparently this isn’t a problem for deep-diving whales, though, so I don’t know how they compensate.

Yes, they would die if you brought a creature like that straight to the surface. You need to stop many times along the way to slowly acclimate the fish as you go up. I watched a video a while ago that ill try and find when I have more time that shows divers doing just this. They puncture a tiny hole in the fish to release the air in the swim bladder, otherwise as they go up it would pop and kill the fish.

@CyanoticWasp with the whales, they’re inhaling O2 on the surface, so it’s compressed on the way down, and restored to it’s original volume when they ascend so there’s no issue. With scuba, you’re taking a full breath of highly compressed air down below, and it will expand as you rise, which is why you need to exhale when you ascend. I’m not 100% clear on how the nitrogen issue works with whales though.

I think I have the answer, @gorillapaws. It’s actually related to what you said about the breath of air that’s taken and compressed in the whale’s lungs on the way down to deeper pressure. The nitrogen in the bloodstream was ‘normal’ at the surface, and is also compressed as the whale dives. As the whale rises, the nitrogen in the blood goes back to normal (sea level) pressure. If the whale had SCUBA gear and could breath compressed air at depth, then rising too quickly to the surface would cause the bends, same as in humans.

Here we go. While granted it doesnt show super deep sea animals, the procedure is the same.
Video
gotta love the voices lol

It wouldn’t be ‘the bends’ that kills them. It would be other, more specific reasons….for example…... If any had a vestige of a swim bladder, it would explode as they rose, but I don’t know what species you’re talking about, and I don’t imagine you do either if you are associating a human vascular disease to a fish.