Re: NANFA-- Osmoregulation in freshwater sharks

Bruce Stallsmith (
Sun, 20 Jan 2002 19:43:16 -0500

>FYI, Jeremy, unlike marine bony fishes, sharks have a higher blood ion
>concentration 2 percent, as opposed to about .2 percent in the bony fishes.
>This higher concentration is due to urea, which would kill bony fishes in a
>concentration so high.
Urea is present in high concentration, but so is another organic salt, TMAO,
which is usually found in a concentration of 2:1 relative to the urea. This
enables sharks to be isotonic (roughtly same salts concentration) relative
to sea water and eases osmoregulatory pressures.

(10 years ago I could have told you off the top of my head what TMAO stands

--Bruce Stallsmith
Huntsville, AL, US of A

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