Re: NANFA-- do fish pee?

Bruce Stallsmith (
Tue, 14 May 2002 10:21:25 -0400

>I used to tease my sisters that they did (along with several thousand other
>things). Inquiring minds want to know if they really do!

Yeah, fishes have very active osmoregulatory systems that involve the
formation and excretion of urine. In short, freshwater fishes are constantly
producing a large volume of dilute urine because they are passively taking
up freshwater from the environment. Saltwater fishes produce small amounts
of very rich urine, because they face the opposite environmental stress:
they are constantly losing water to the surrounding environment by passive
osmosis. The various sharks and rays have a different strategy for
osmoregulation that involves trying to conform to the surrounding waters, in
part by suffusing their body tissues with urea (a nitrogenous compound).
Even so, they still have active kidney systems for ionic regulation via
urine formation.

The environmental biology of animals and plants always comes down to poop
and sex, so I guess this is one facet.

--Bruce Stallsmith
Huntsville, AL, US of A
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