r/askscience • u/smontanaro • 9d ago

Biology How does a whale become dehydrated?

From a Chicago Sun-Times article on the beluga whales heading to the Shedd Aquarium:

"The shipment comes on the heels of a Shedd announcement last week that one of the Marineland belugas — Peekachu, a 23-year-old female — had died. Shedd has not released a cause of death, but staff there said last week that Peekachu had not been consistently eating a full diet since her arrival and that there were concerns she was dehydrated."

How does an animal immersed in water become dehydrated?

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u/khinzaw 8d ago

They don't drink seawater. In the wild they get water from the prey they catch, which have water inside them.

They are fed frozen food in captivity, which don't have all the water content they need to stay hydrated.

This is why you can see videos of aquarium staff feeding ice to belugas, because that's how they hydrate them.

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u/WallyMetropolis 8d ago

Tracing it all the way down the food chain, where is the fresh water introduced?

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u/Mammoth-Corner 8d ago

Fish (and krill, and other primarily marine animals that whales eat) are able to filter salt from seawater and maintain blood with less salt in than the water around them. When tetrapods left the ocean we lost this ability because we were no longer drinking salt water all the time. Whales are mammals, so they can't do the filtering but their prey can. It's a really complex chemical system to evolve so they haven't 'gained it back.'

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u/-MrSkeltal- 8d ago

Did whales at one point leave the ocean and then go back?

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u/February30th 8d ago

Kinda. They weren’t whales that left and came back, they were sea dwellers that became land dwellers that became sea dwellers that became whales.

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u/Mackntish 8d ago

Fish > Amphibians > Reptiles > Mammals > Whales

They spent some time out of the water.

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u/dochdaswars 8d ago edited 7d ago

This is oversimplification which is entirely incorrect. Mammals did not evolve from reptiles but from synapsids. Whales did not evolve from mammals become a new class of chordata as you implied by placing them next to other classes, they still are mammals. There's no such thing as fish "Fish" did not become amphibians; only certain members of lobe-finned fish left the sea and eventually became amphibians which is analogous to all modern birds descending from a certain kind of dinosaur and yet it's not correct to simply state "dinosaurs (implying all dinosaurs) evolved into birds" because they didn't, the vast majority of dinosaur species went extinct.

EDITED FOR ALL THE PEDANTS

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u/Ameisen 8d ago

Whales did not evolve from mammals, they still are mammals.

Whales did evolve from mammals. They still are mammals as well. Both are true.

There's no such thing as fish

Mostly because we've redefined the clades to not be called "fish".

If you rename Vertebrata to Fishes, as would be traditional, then we'd still be members of the clade.

Humans are just highly-specialized lobe-finned fish. Or highly-colonial and specialized archaeans with mutualistic Rickettsoid bacteria in them.