View Full Version : A question about Fish

07-25-2007, 06:46 PM
So you catch a fish in a net
lets us call him/her - wasabi
While wasabi is in the boat and you are untangling all the jellyfish, crabs, seaweed other fish etc,
wasabi has been breathing pure oxygen for more than 15 minutes

yet wasabi still lives.

fish filter oxygen through their gills via the water

Why can a fish not survive full time above water?

(the above image does not represent Nemo unless you want it to)

07-25-2007, 06:50 PM
Lung fish can

Good to see you back :)

07-25-2007, 06:53 PM
Never thought about it, but probably something to do with how the oxygen is received when passing over the gill. :huh:

Same reason we can "breathe" the oxygen while under water.

07-25-2007, 06:55 PM
pressure of oxygen maybe?

@wzrd :)

07-25-2007, 06:56 PM
You got me curious now.

/me runs off to Google.


07-25-2007, 07:04 PM
wasabi has been breathing pure oxygen for more than 15 minutes
I normally don't bring a tank of that with me when I go fishing. Are you trying to save any fish that might have gill cancer or something?

07-25-2007, 07:11 PM
Fish gills are remarkable things, but the conditions under which they function are pretty specific. For one thing, they are rather delicate, and their tremendous surface area (the main thing that makes them work so well) is dependent on being immersed in water to support their weight. 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.
If it were possible to keep the gills supported and moist without being submerged, a fish could survive quite a bit longer, but that isn't physically possible even in a humid air-filled chamber at zero gravity, the gill filaments will simply adhere to one another. Water needs to completely fill the gill chamber to keep all of the filaments in operation. 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 50% efficiency, since the water flow needs to go counter to the flow of blood for maximum oxygen uptake.
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. But land-based critters 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, so I don't think liquid breathing systems are going to be easy to design or use.

:source: (http://www.straightdope.com/mailbag/mfishbreath.html)

07-25-2007, 08:56 PM
What does disabled privs mean.

07-25-2007, 08:59 PM
not allowed into the invite secton