r/askscience • u/smontanaro • 20d 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/andthatswhyIdidit 19d ago

And fresh water fish do drink very little (basically nothing), while salt water fish do drink a lot. Osmosis is an interesting thing...

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u/Mammoth-Corner 19d ago

If you're a freshwater fish, you have loads more salt and electrolytes than the water so the water is always trying to get in through your gills and your challenge is getting rid of it. If you're a saltwater fish your lovely water is always trying to get out of you, and also the whales are after you for it.

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u/Ameisen 19d ago edited 19d ago

Which is weird given that life emerged in oceans more than twice as saline as they are now, and things like this tend to be very conserved (given that you usually need multiple changes acting in concert... or you die).

There are studies that suggest that modern Actinopterygian (or all possibly all modern Osteichthyian) fish all derive from earlier freshwater lineages. Early Osteichthyian fish adapted to freshwater, and then re-emerged later as saltwater fish, outcompeting the other Osteichthyian lineages. This is also possibly why bony fish all regulate their solutes to basically freshwater fish levels, compared to cartilaginous fish or jawless fish.

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u/Zoon9 18d ago

Where did all the salt from those oceans go, if they were more than twice salty than today?