If you have a pet, one of your jobs might be to make sure that your pet has plenty of food and water...unless, of course, your pet is a fish!

You have to feed your fish, but you don’t have to give them water — there’s water all around them! But do fish need to drink that water?

Well, some fish do, but some don’t! It all depends on where they live. You probably already know that your body needs water—for lots of reasons!

It’s so important, in fact, that different parts of your body work together to make sure that there’s about the same amount of water inside of it at all times. If the amount of water gets too low, you get thirsty, and grab a drink. And if the amount of water gets too high, you get rid of the extra when you pee.

Well, fish also need to keep the right amount of water on the inside of their bodies. And the water outside of a fish’s body can affect whether that fish needs to drink water, or not. Most fish live in one of two kinds of water.

Some fish, called freshwater fish, live in places where there’s no salt in the water— like lakes, ponds, and rivers. Other fish, called saltwater fish, live in water that has lots of salt in it, like the ocean. Freshwater fish have an easier time keeping the right amount of water inside of their bodies.

That’s because water enters into a freshwater fish’s body right through its gills. Gills are the body parts that fish use to breathe. Fish breathe by pulling water into their mouths, then pushing the water over their gills and out of their body.

And in freshwater fish, gills also end up taking in some of the water, and the fish ends up with more water in its body. So freshwater fish don’t really have to drink water through their mouths like we do. These fish actually have to make sure they don’t get too much water, and their body has to work very hard to get rid of the extra water as waste.

While freshwater fish get a lot of water in through their gills...saltwater fish lose a lot of water through their gills. As water flows over a saltwater fish’s gills, the salt that’s in the water outside of the fish’s body sucks out some of the water that’s inside of the fish’s body through its gills. Since water is always moving over a fish’s gills, that means water is always leaving a saltwater fish’s body.

And that means that the fish that live in saltwater need to drink—a lot. Most animals can’t drink salt water when they’re thirsty, but these fish can! They gulp and swallow water almost constantly.

Saltwater fish have a special system in their bodies that takes salt and puts it back out into the ocean…and everything stays in balance! So, some fish need to drink water, and some don’t...it just depends on where they live! Thanks for joining us here on SciShow Kids!

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