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Thread: Gills: Fresh water fish vs Sea water?

  1. #1 Gills: Fresh water fish vs Sea water? 
    Forum Cosmic Wizard icewendigo's Avatar
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    Can fresh water fishes breathe sea water, and ca a typical sea fish breathe in a fresh water lake?


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  3. #2  
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    Well some fish can and do, indeed for some fish it is an essential part of their life cycle to change from one to the other. Eels are generally fresh water during parts of their life then migrate to the open sea to for a good part of their lives then return back to the same fresh water locations they started from. Salmon do the same, hatch in the upper reaches of rivers, then swim to the sea to mature returning to fresh water to spawn. Barramundi live in the inbetween zone, but can survive on both fresh and salt water.

    But of course there are many fish that are well adapted to either a fresh water environment or a salt water one. If a fish lacks the ability to keep fluids inside then if they were to move into salt water the osmotic pressure difference between the fishes body fluids and salt water would force the fluids out of the fish dehydrating it.

    Likewise if a fish has developed mechanisms to prevent that osmotic difference from killing it by having say a zero difference in salt water, then it could be in danger of absorbing too much water in a fresh water environment as the pressure difference is now reversed.

    Osmosis causes the water always to flow from the more dilute to the more concentrated solution through any membrane. For a fish to be able to survive a range of different environments it must have the ability to overcome these problems, it could perhaps tolerate different body fluid concentrations, or it could have processes to actively counteract the natural osmotic tendencies, the way we use our kidneys to keep our body fliud concentrations within a tight range.
    - Osborne


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    Forum Cosmic Wizard icewendigo's Avatar
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    Is it fair to say that in many cases where a fish is not adapted for the correct water salt concentrations, the fish (in the wrong water) will die in a time frame that is more similar to a human being dehydrated because he cant drink (dead in a number of days) rather than being similar to a human deprived of breathing air (dead in a matter of minutes)?
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    Forum Bachelors Degree dmwyant's Avatar
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    You have a hypothesis now create an experiment to test it
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    Forum Radioactive Isotope skeptic's Avatar
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    Ouch!

    Dropping a goldfish into a coastal salt water rock pool would be cruel, and the result predictable. So please do not carry out any experiments.
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  7. #6  
    Forum Professor Zwolver's Avatar
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    A fish's gills are a thin layer of cells with many blood vessles running trough. Ideal for a fast and relatively efficient oxygen transport system. Though the advantage of the system brings some problems. The osmotic value have to be similar. A difference to big, and cells will burst or dehydrate. Some fish can live in eiter salt or fresh, this has something to do with the mucal layer that fish have on their gills. The thicker the layer, the less oxygen efficiency, but the more fluctuation tolerance to the osmotic value of the water.

    An experiment should only have to be a swab across the gills of the fish, a sample of the blood, or a monster of the cells. Still rather you don't experiment on animals at all.
    Growing up, i marveled at star-trek's science, and ignored the perfect society. Now, i try to ignore their science, and marvel at the society.

    Imagine, being able to create matter out of thin air, and not coming up with using drones for boarding hostile ships. Or using drones to defend your own ship. Heck, using drones to block energy attacks, counterattack or for surveillance. Unless, of course, they are nano-machines in your blood, which is a billion times more complex..
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    Forum Cosmic Wizard icewendigo's Avatar
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    THanks Iceaura I got this from the livestrong link

    "
    Body tissues in a saltwater fish contain less salt than the water in which it lives. Because the saltier environment in the outside water draws water from body tissues, a saltwater fish constantly loses water through its skin and gills. To compensate and prevent dehydration, a saltwater fish drinks large quantities of saltwater, produces very little urine and secretes salt from this water through its gills.

    In contrast, body tissues in a freshwater fish contain more salt than the water in which it lives. As a result, water continually flows into the body of a freshwater fish through its skin and gills and the fish has no reason to take in additional water by drinking. Freshwater fish avoid an excess of water in body tissues by producing large amounts of urine.
    "

    I wont do experiments, but will consider "likely" that a fish can survive a couple of hours or more in the wrong water type, and that being immerse in the wrong water type for a few minutes is less dangerous than being out of water for a few minutes.


    ~ Fish drinking water or urinating: I love this science site for that, I often learn something new
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    Last edited by icewendigo; May 14th, 2012 at 11:57 AM.
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