How do fish survive in deep sea and why do they die when you take them to water higher up?

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How do fish survive in deep sea and why do they die when you take them to water higher up?

In: Biology

Probably the oxygen levels in the fish’s blood?

Water pressure increases as depth increases. A fish that is born and lives it’s entire life deep has a body used to those environmental conditions. When a fisherman reels in a fish like this, it’s eyes and such puff out and can kill the fish if not returned back to the water quickly. If the fish can return back to depths in time no permanent damage will be done.

Fish have what is known as swim bladders. These are the same in principle as the ballast tanks on submarines. They fill these with water to control their buoyancy. But unlike submarines they cannot just blow all the water out so a deep sea (deep water, probably applies to deep lakes too) fish that is pulled rapidly up has the water in these bladders expand to the point that they burst. Besides it probably being painful the fish cannot regulate its buoyancy and will flay and flounder in the water till it dies or is eaten.

As for survival they are simply made to be able to withstand the greater pressures. It helps to be filled with water and cartilage instead of giant gas bags and rigid bones like we have, we simply don’t compress very well. That is why for a while the navy was experimenting with an oxygen emulsion for deep divers to breath, similar to the amniotic fluid that we all breathe for 9 months.

Basically, pressure isn’t a problem to living things. *Change in pressure* is the problem. A living thing that lives its whole life at deep pressure is adapted to that pressure, and most of those organisms can only survive a narrow pressure range. Getting out of that range would require many generations, each moving a bit further.

Only a few complex organisms can survive dramatic changes in pressure, and they require some pretty extensive adaptions to do so.