Even though air has 20-40 times as much oxygen as water, why do fish suffocate if exposed to air?

Question

Some fish drown or suffocate if they don't keep swimming, and almost all fish suffocate if taken out of the water and exposed to air, even though air has 20-40 times as much oxygen as water does. Why is this?

Answer 1

b/c their bodies are used to getting ther O2 through a liquid. so when they suffocate in air it is nop different if we drown in water (b/c we are used to breathing air).

Answer 2

The fish gills are able to pass and extract oxygen from the water. By the same token, we humanoids would drown if we tried to extract our oxygen from water. Our lungs are for extracting from the air only.

Answer 3

Fish don't actively breath in air like humans, the oxygen diffuses across their gills and enters their blood stream that way instead of a complex respiratory system with lungs. So, fish have to keep swimming in order to keep the water flow across their gills. Once out of water, lack of water and gravity causes the gills to close, because the water and buoyancy keep the gills open. Once this happens, the fish can't absorb oxygen regardless of how much is actually available to it.