caribbean reef octopus deposit photos

Is There Such A Thing As A Freshwater Octopus?

You can find octopuses just about everywhere in the ocean—from tidepools to the deepest oceanic trenches. So octopuses can survive anywhere there’s water, right? Even freshwater? Not quite. While octopuses have the impressive ability to change and adapt both as individuals and as a species, there’s one thing all octopuses must have to survive, and that’s salty seawater. Let’s find out if there really is a type of freshwater octopus out there!

red coconut octopus depositphotos
Octopus Cyanea (Day Octopus)

Blame osmosis

Despite some fun legends about giant lake octopuses, there’s no such thing as a freshwater octopus. And that’s because octopuses’ bodies are built for saltwater, and no known octopus species in the very long history of octopus species have adapted to live out its life in freshwater.

Put any animal that’s adapted to seawater into freshwater, and the same process will eventually kill it: osmosis

Osmosis is the process by which molecules from a more concentrated solution pass through semipermeable membranes (like those of an animal’s cells) into a less concentrated solution, eventually equalizing the concentration on both sides. 

When you put an animal with salty blood into water that’s not salty, freshwater will flood its cells, causing them to swell and ultimately burst. This is called cytolysis

Osmosis is also the reason freshwater species can’t survive in the ocean, except in this case, the freshwater within an animal’s cells will leave the cells, causing them to shrivel up and stop working. 

🐙 Octopus Fun Fact

Some marine animals, like salmon and green crabs (Carcinus maenas), can survive in both freshwater and seawater. These animals have the inner mechanisms to adapt their bodies to varying levels of salinity (saltiness) in their surroundings. 

Octopuses can do many cool things, but this is NOT one of them.

Not Safe For Work Octopus GIF by SnappyTV - Find & Share on GIPHY

But I saw a video on the internet!

Every once in a while, someone spots (even records!) an octopus in a body of freshwater or brackish water (a mixture of seawater and freshwater).

While an octopus can tolerate these hostile conditions for a while, its swelling cells will eventually stop working, and the octopus will not survive. 

How do these octopuses end up in fresh or brackish water?

In some cases, an octopus may have migrated there from the ocean because the water is tolerably salty. In other cases, it may have been a former pet released by a human into the wrong sort of water. 

Weird things happen, but the bottom line is that if an octopus is in freshwater, it’s not supposed to be there. 

Common Octopus

🐙 Octopus Fun Fact

Octopuses’ inability to survive in freshwater runs in the family. All cephalopods—including squids, nautiluses, and cuttlefishes—are strictly ocean dwellers. 

Keep it salty

TLDR: There’s no such thing as a freshwater octopus!

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