Why can't fish breathe on land?

Question

10 points to the first person who knows the correct answer to why fish really can't breathe on land (or any animal with gills for that matter).

Additional Details

Think along the lines of simple, the answer is a lot simpler than you think.

Think of why humans cant breathe in water and try to figure out why fish cant breathe on land in that aspect.

Ok guys we have a winner, read annalyn's answer..just the first paragraph is sufficient enough.

Fish could in fact breathe on land if their gills had enough support but they collapse out of the water, they need the water for support. Gills have the ability just as lungs to take in oxygen from any medium but just arent strong enough on land.

All i was looking for was that they collapse on land. Thanks to all for your efforts. Best answer will be given when the four hours is up.

Answer 1

Best Answer - Chosen by Asker

Fish gills are very delicate, and have a very large surface area (which makes them work so well). It is completely dependent on being immersed in water to support their weight. Out of the water, the delicate gills will collapse like wet tissue paper, and very little surface area is left exposed, so gases can not be properly exchanged. Therefore, most fish can't survive out of the water for a long time, because oxygen deficiency will catch up with them and they asphyxiate.

If we could find a way to keep the gills supported and moist without being immersed, a fish could survive for a lot longer, but this it isn't physically possible, even in a humid air-filled chamber at zero gravity, considering that the gills would just stick to one another. Water must completely fill the gill chamber to keep everything else in working order.

For that matter, the water has to be flowing in the mouth and out the gills in order for oxygen extraction to work properly. If you force water to go in the opposite direction, in the gills and out the mouth, the system only works at about half the efficiency, since the water flow needs to go counter to the blood flow for maximum oxygen intake.

Many fish species have evolved mechanisms to work around this limitation (usually involving the development of lung-like structures in addition to the gills), and some can go for long periods out of water (like the Beta fish). But land-based creatures haven't developed a comparable ability to breathe while submerged. The lungs of other vertebrates are simply not designed to extract enough oxygen for them to function underwater, where the oxygen concentrations are more than an order of magnitude lower. If water could hold about 20 times more oxygen than it does, things would be different – there are apparently a few liquids (though not water) that can hold that much dissolved oxygen, and one can breathe a liquid of this sort, as in the movie "The Abyss". But maintaining those high oxygen levels for long in a closed system might be a major practical stumbling block.

Asker's Rating:

Asker's Comment:

Although i know this came from an outside resource it was the answer i was looking for, thanks.

Answer 2

they need oxygen to live and fishes do not have lungs , they have gills

Answer 3

Because they extract oxygen from water that flows through their gills. They can't extract it from the air.

Answer 4

They aren't land animals.

Answer 5

The same reason we can't breath under water.

Answer 6

Some can actually. Walking Catfish can.

Answer 7

the water passes through the gills and it takes the oxygen out of the water... i think lol

Answer 8

Because their gills are designed to remove oxygen from water, not air. The oxygen transfer takes place from the water.

Kind of opposite that your lungs can't absorb oxygen from water. You choke on water. The fish chokes on air.

Answer 9

I think it's got something to do with the water needing to run along their gills, like it activates the oxygen retrieval or something.

I seem to remember something about that in high school biology. Several years ago.

Answer 10

that would make them reptiles and not amphibians

Answer 11

their gills can only take oxygen out of water.

Answer 12

they drown on land like we would drown if we were in water... ? blah. retarded.

Answer 13

Cause fish take water and split it into hydrogen and oxygen. They take most of the oxygen and some of the hydrogen so in all oxygen they got no hydrogen. That's my best guess.

Answer 14

bc they do not like the smell of the air, kind of like how we do not like the taste of water.... duhh...

Answer 15

bc their respiratory system is not adapted to breathing air, just like your respiratory system isnt adapted to breathing in water. shall i go into the details of breathing?

Answer 16

Fish can't breathe on land because they have gills. And gills help them breathe in the water. Fish are delicate. Out of water, the gills collapse like wet tissue paper, and very little surface area is left exposed for gas exchange. Most fish, therefore, can only survive a short time out of water before oxygen deficiency catches up with them and they asphyxiate.

Answer 17

They can for a moment but the problem is, simply, they dry out and die.

Answer 18

unlike lungs that tranfer oxygen from the air gills take it from water .