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  • All living things on Earth need water, because the chemical reactions that make life possible

  • happen in an aqueous solution.

  • Which means us land animals have to drink it to keep it inside of us all the time.

  • Butwhat about fish?

  • It seems like since theyre always in the aqueous solution of whatever body of water

  • theyre swimming around in, they wouldn’t need to actually drink the stuff.

  • But it turns out that some fish actually do need to drink. And others do not.

  • It depends on the fish, and what kind of neighborhood it lives in.

  • Water, you should know first of all, is really into finding a balance.

  • If you have a membrane that water can pass through, and there are different concentrations

  • of salt on each side, then the water will always flow toward the saltier side of the

  • membrane, until the concentrations on both sides are the same.

  • That means that freshwater fish have it easy.

  • Since the concentration of salt in their bodies is higher than the concentration in the water,

  • that fresh water just flows right in, mainly through their gills, and into their bloodstream.

  • They also swallow some water when they eat -- I mean, it’s kind of unavoidable -- but

  • they don’t need to actively gulp down water.

  • But, in order to retain that balance of concentrations, the fish’s tissues still need to have some

  • salt in them.

  • And that’s where chloride cells come in.

  • These are special cells in the gills that produce large amounts of an enzyme that controls

  • the flow of dissolved salts -- like sodium and potassium -- across cell membranes.

  • So, in freshwater fish, these chloride cells work hard to bring just the right amount of

  • salt into the fish’s bloodstream.

  • Now, saltwater fish have the opposite problem.

  • For most of them, the concentration of salt in the water is higher than the concentration

  • in their blood.

  • That means that as they pass water over their gills to breathe, the higher concentration

  • of salt outside of their body is constantly sucking water out of them.

  • So these fish have to drink a lot, which they just gulp down by the mouthful.

  • But since the only water around is salty, they have to filter out the salt to make it

  • safe for them to absorb.

  • A lot of that salt is filtered out in the fish’s kidneys.

  • But these fish have chloride cells in their gills, too. It’s just that, in their case,

  • those cells are constantly pumping salts out of the bloodstream and into the saltier water.

  • So they may be surrounded by water, but no matter where they live, fish are always looking

  • to find that balance.

  • Thanks for asking. If you have a quick question you'd like to ask us, we're down in the comments

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All living things on Earth need water, because the chemical reactions that make life possible


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B1 中級

魚會喝水嗎? (Do Fish Drink Water?)

  • 330 10
    Jeff Hsiao 發佈於 2021 年 01 月 14 日