Why are there no fish in the deepest deep sea?

R. R. Helm in Deep Sea News:

ScreenHunter_1353 Sep. 04 17.19Here’s a mystery: below 8,400 meters there are no fish. There are other creatures: sea cucumbers, anemones, tiny worms, but no one has ever seen a fish. At 8,370 meters? There are fish. But not below 8,400 meters. At its deepest the ocean reaches roughly 11,000 meters, so there is plenty of space. And right below 8,400 meters it’s equally cold, equally dark, equally middle-of-no-where as it is right above 8,400 meters. But there is some magic line at 8,400 meters, below which fish apparently cannot go. No one understands why this line exists. Or if perhaps one day we’ll find a fish that can, in fact, cross it. But for now, scientists do have some ideas.

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