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Author Topic: How do fishes breathe?  (Read 3566 times)

Offline yor_on

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How do fishes breathe?
« on: 18/12/2009 00:43:44 »
I've been thinking of how fishes breath and wondering why we can't use it too?
So my question is twofold.

1. How exactly do a fish get it's oxygen from the surrounding water. And I do mean 'exactly' :)
2. And why don't we copy it? Or do we?
« Last Edit: 18/12/2009 11:29:50 by chris »


 

Offline Chemistry4me

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Re: How do fishes breathe?
« Reply #1 on: 18/12/2009 00:45:55 »
1. Diffusion
2. We have a tidal system which isn't really like the fish, they've got unidirectional flow of water across their gills.
 

Offline yor_on

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Re: How do fishes breathe?
« Reply #2 on: 18/12/2009 00:56:52 »
Diffusion? Filtering out the oxygen you mean?
How do they do it and how much area does those filters take versus bodyweight?

How about submarines, couldn't they use it. And divers.
I mean if a fish can?

Heck ain't we supposed to be the crown of creation :)
 

Offline Chemistry4me

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Re: How do fishes breathe?
« Reply #3 on: 18/12/2009 01:02:53 »
Diffusion? Filtering out the oxygen you mean?
How do they do it and how much area does those filters take versus bodyweight?

How about submarines, couldn't they use it. And divers.
I mean if a fish can?
They've got tiny membranes on the gill filaments called lamellae in which there are capillaries. The blood flows one way and the water flows the other way (counter current flow) so there is a constant concentration gradient allowing oxygen from the way to diffuse into the blood.
 

Offline yor_on

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Re: How do fishes breathe?
« Reply #4 on: 18/12/2009 01:40:49 »
So?

Couldn't we too use it in some way instead of electrolysis?
Like osmosis through some permeable skin.

It would be a cool way to dive :)
 

Offline Madidus_Scientia

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Re: How do fishes breathe?
« Reply #5 on: 18/12/2009 03:07:16 »
The difference between lungs and gills is mostly that gills have alot more surface area to compensate for the decreased amount of oxygen in water compared to air, and they can only achieve this amount of surface area because they are effectively weightless underwater, all the fine capilleries etc. can float and do not collapse onto each other due to gravity. Out of water, their gills collapse and they cannot breathe.
 

Offline yor_on

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Re: How do fishes breathe?
« Reply #6 on: 18/12/2009 05:41:24 »
Okay, nice explanations, but I still feel we should be able to use it somehow. It seems such an elegant solution.
 

Offline chris

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How do fishes breathe?
« Reply #7 on: 18/12/2009 11:39:47 »
The comprehensive answer is that gills and lungs provide an extensive but thin surface area across which gas exchange can occur with blood.

Blood contains the pigment haemoglobin, which has a higher affinity for oxygen than the surrounding water (or air in the case of a lung). Consequently, oxygen is absorbed from the water, associates with the haemoglobin, is removed from the exchange surface by blood flow and then distributed via this route to the dependent tissues.

This removal of oxygen from the exchange surface maintains a steep concentration gradient between the oxygen concentration in the water and the blood; the gas moves down this concentration gradient by diffusion. Since the rate of diffusion is proportional to 1/distance squared (as shown by Einstein) the exchange surfaces (i.e. membranes) must be very thin to work effectively.

I believe gills also make use of a counter-current exchange effect to maximise efficiency. That is, water flows across the gill surface in the opposite direction to the flow of blood. Consequently water containing the most oxygen sees blood containing the highest level of oxygen first, thereby maintaining the concentration gradient and maximising oxygen pick-up.

Chris


 

Offline Don_1

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How do fishes breathe?
« Reply #8 on: 19/12/2009 14:48:01 »
I seem to recall a membrane being produced, many years ago, which did allow gaseous exchange. I'm sure it was reported on the BBC's 'Tomorrows World' programme, which shows how far back I'm going. But I have no idea what happened to this membrane. Probably one of those bright ideas which proved to be a non-atarter.

But there has been work on an artificial gill.
 

Offline yor_on

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How do fishes breathe?
« Reply #9 on: 23/12/2009 13:37:13 »
It should be a membrane wrinkled like the lungs I guess to get the best effects, and there have to be a water flow. Fishes produces it naturally as they swim and so should a diver be able to do but when hovering there need to be some other way. and it would be osmosis working too, wouldn't it?

-------

Nice link btw :)
 

Offline Geezer

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How do fishes breathe?
« Reply #10 on: 23/12/2009 16:41:45 »
Q: If fish don't have a nose to breath through, how do they smell?
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A: Terrible!

(Oi! - No need to shove. I was just about to leave anyway.)
 

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How do fishes breathe?
« Reply #10 on: 23/12/2009 16:41:45 »

 

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