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Thread: How do fish use water?

  1. #1 How do fish use water? 
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    I've always been told that salty water isn't good to consume. So, how is it possible for fish to drink water, is there any system of filtration or maybe osmosis that allows them to get pure water?


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  3. #2  
    ▼▼ dn ʎɐʍ sıɥʇ ▼▼ RedPanda's Avatar
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    We learn something new everyday...

    From a google search I found:
    "Fresh water fish absorb water through their skin and gills, saltwater fish actually do drink water.
    In saltwater fish, they have to drink because their body's concentration of salt is lower than the surrounding water. Therefore, they have to drink huge amounts of water every day to stay hydrated.
    In freshwater fish, their salt concentration is higher than that of the surrounding water, and, as osmosis dictates, they absorb water through their highly permeable skin. To keep from bursting, freshwater fish actually have to excrete water, up to 10 times their body weight daily, unlike saltwater fish."
    http://wiki.answers.com/Q/Do_fish_drink_water

    Or a longer version:
    http://www.upendedblog.com/2011/10/25/obvious-questions-in-science-how-do-fish-drink

    In summary:
    Freshwater fish don't drink; they absorb.
    Salt water fish don't absorb; they drink.

    p.s.
    There are many reasons for humans to not drink salt water (e.g. it is an emetic and a diuretic).
    But just because humans are unable to consume salt water, doesn't mean other animals are also unable to.


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    Some humans I know absorb alcohol just as fish do water! jocular
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  5. #4  
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    @RedPanda: Thank you for your answer.
    I've also read that some aquatic mammals eat other organisms living in their environment to get the fresh water they need and hydrate themselves.
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    ▼▼ dn ʎɐʍ sıɥʇ ▼▼ RedPanda's Avatar
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    Quote Originally Posted by Newpierre View Post
    @RedPanda: Thank you for your answer.
    I've also read that some aquatic mammals eat other organisms living in their environment to get the fresh water they need and hydrate themselves.
    Yes - the ones that initially spring to mind are dolphins; all their water comes from eating fish.
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    Quote Originally Posted by Newpierre View Post
    @RedPanda: Thank you for your answer.
    I've also read that some aquatic mammals eat other organisms living in their environment to get the fresh water they need and hydrate themselves.
    And, even for humans, in "normal" conditions we get pretty much all the water we need from our food.
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    Quote Originally Posted by RedPanda View Post
    To keep from bursting, freshwater fish actually have to excrete water, up to 10 times their body weight daily, unlike saltwater fish.
    A good reason to swim in the ocean, rather than a lake. (Although there is the minor quibble that some things in the ocean can eat you.)
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  9. #8  
    ▼▼ dn ʎɐʍ sıɥʇ ▼▼ RedPanda's Avatar
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    Quote Originally Posted by Neverfly View Post
    Quote Originally Posted by RedPanda View Post
    To keep from bursting, freshwater fish actually have to excrete water, up to 10 times their body weight daily, unlike saltwater fish.
    (Although there is the minor quibble that some things in the ocean can eat you.)
    That reminds me of when I was planning my trip to New Zealand: "There are no dangers in NZ.......apart from sharks and meningitis."
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  10. #9  
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    Quote Originally Posted by RedPanda View Post
    We learn something new everyday...

    From a google search I found:
    "Fresh water fish absorb water through their skin and gills, saltwater fish actually do drink water.
    In saltwater fish, they have to drink because their body's concentration of salt is lower than the surrounding water. Therefore, they have to drink huge amounts of water every day to stay hydrated.
    In freshwater fish, their salt concentration is higher than that of the surrounding water, and, as osmosis dictates, they absorb water through their highly permeable skin. To keep from bursting, freshwater fish actually have to excrete water, up to 10 times their body weight daily, unlike saltwater fish."
    http://wiki.answers.com/Q/Do_fish_drink_water

    Or a longer version:
    http://www.upendedblog.com/2011/10/25/obvious-questions-in-science-how-do-fish-drink

    In summary:
    Freshwater fish don't drink; they absorb.
    Salt water fish don't absorb; they drink.

    p.s.
    There are many reasons for humans to not drink salt water (e.g. it is an emetic and a diuretic).
    But just because humans are unable to consume salt water, doesn't mean other animals are also unable to.
    It is also why it is not a culinary thing to NOT salt fish....you salt it....like any other food. (always just a little though)
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  11. #10  
    Theatre Whore babe's Avatar
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    Quote Originally Posted by Neverfly View Post
    Quote Originally Posted by RedPanda View Post
    To keep from bursting, freshwater fish actually have to excrete water, up to 10 times their body weight daily, unlike saltwater fish.
    A good reason to swim in the ocean, rather than a lake. (Although there is the minor quibble that some things in the ocean can eat you.)
    Dang sea turtles. Though honestly, before I went off island, we had a S&R and one CG heli searching for a kayak fisher probably dumped it with too big of a fish for a single seater. They found the kayak, but not him, but a few UNUSUALLY large tiger sharks. After two days, they stopped looking.
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