Are There Any Freshwater Octopus? (Surprising Facts)

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Brazilian reef octopus
Octopuses are highly intelligent creatures that can be found in practically every type of reef ecosystem. Don Loarie / CC BY 4.0

Known for being some of the most intelligent invertebrates to have graced our seas, octopuses have developed many adaptations for survival in marine environments. They are members of the class Cephalopoda, which also includes soft-bodied mollusks like squid and cuttlefish. Present in practically every type of reef ecosystem, their radial shape and tentacle-covered appendages allow them to expertly swim, squeeze into small caves, and evade potential predators.

Though octopuses are found in both shallow and deep oceanic waters, they are not known occupants of freshwater systems. Their tolerance for a diverse range of habitats does not extend into waters that are wholly devoid of dissolved salts. Some species, such as the pouched octopus (Cistopus platinoidus), have been sighted in estuarine or brackish environments.

It is highly unlikely that any octopuses found in ponds, rivers, or lakes are there by choice. Sightings of inland octopuses may simply be associated with the harsh currents of an increasing tide, attempted escape from a marine predator, and the irresponsible release of a pet octopus or of marine bycatch. Though these unfortunate octopuses may tolerate hostile conditions for some time, they simply cannot survive in freshwater due to their body’s physiology.

What Would Happen to an Octopus in Freshwater?

Blue sea star
Many marine invertebrates, such as starfish and octopuses, function as osmoconformers in saltwater. This means that they match their internal fluid concentration to that of the environment they’re in. Alberto Alcalá / CC BY 4.0

Octopuses have not developed adaptations for coping with the osmotic changes between saltwater and freshwater. In freshwater, where their bodies would undoubtedly have a higher concentration of nutrients, salts, and minerals than their surrounding fluid environment, their cells are likely to swell and eventually stop working.

In saltwater, octopuses and many other marine invertebrates (e.g. starfish, sea urchins, jellyfish) function as osmoconformers. They remain “isotonic” with seawater by matching their internal fluid concentration to that of their environment. There’s virtually no such thing as an obligate freshwater osmoconformer. Diluting one’s body fluids to match the concentration of freshwater would significantly compromise basic organ functions, which is why freshwater animals are usually osmoregulators.

Forcing an octopus to remain in freshwater would be cruel. These conscious animals are able to experience pain and will likely try to escape freshwater bodies or enclosures in the hopes of finding a more suitable habitat. These sophisticated cephalopods, even those that are sold as pets for aquarium hobbyists, should be neither acclimatized nor homed in a freshwater tank.

Myths About Octopus-Like Creatures in Lakes

Illustration of kraken attacking ship
There are many different stories of giant mythical octopuses, such as the Kraken (pictured). Edgar Etherington, Public domain, via Wikimedia Commons

Giant octopuses are often the subject of mythical lore, especially in towns around deep lakes. Even experienced fishermen may claim to have repeatedly caught sight of a mysterious, multi-limbed creature that rises from the depths when it is least expected. They may go so far as to describe their massive tentacles. Oftentimes, unexplained disappearances of lake swimmers and boats are attributed to octopus-like lake monsters.

The ‘Oklahoma octopus’, for example, is one of the most popular mythical lake monsters in the US. Blamed for several drowning incidents in Lake Thunderbird, Lake Oologah, and Lake Tenkiller, it is said to be as massive as a horse, have red-tinged brown skin, and, of course, tentacles. The ‘Kraken’, a legendary, octopus-like sea monster, may also occasionally be blamed for mysterious disappearances in inland waters that are connected by large rivers to the coast.

There has yet to be proof that these lake creatures actually exist, and it is unlikely that there will be scientific findings to prove their existence anytime soon. While there may, indeed, be massive carnivores that are inadvertently associated with the loss of humans in lake systems, they are probably not your typical osmoconforming octopuses.

Unless these so-called lake monsters are truly mutants of the deep that appear once in a blue moon, they are more likely to be freshwater sharks or carnivorous catfish. Regardless, their myths live on and may actually do more good than harm as they encourage lake-goers to be more cautious of their surroundings.

Angeline L
About the author

Angeline L

I'm a passionate researcher and scuba diver with a keen interest in garden plants, marine life, and freshwater ecology. I think there’s nothing better than a day spent writing in nature. I have an academic and professional background in sustainable aquaculture, so I advocate for the responsible production of commercial fish, macroinvertebrates, and aquatic plants.

Read more about Pond Informer.

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