Kidney and salt water

From: pita admininstrator (
Date: Thu Sep 14 2000 - 14:08:34 EDT

---------- Forwarded message ----------
Date: Thu, 14 Sep 2000 08:31:39 -0400
From: Phil Clapham <>
To: Ron McGinley <>, Address Ask2 <>,
    Mike Williamson <>
Subject: Salt water environment


In the case of cetaceans (whales, dolphins and porpoises), the major
adaptation relates to the obvious need for fresh water. To deal with
this, cetaceans extract water from their prey, but also have remarkably
specialized kidneys that can deal with the demands of high salt intake.

The situation varies with species, however. In the case of most
dolphins and porpoises which feed on fish (or, as with some killer
whales, on other mammals), their prey does not contain high salt levels,
and it seems very likely that direct ingestion of sea water during
feeding is minimized. This also applies to baleen whales when they feed
on fish. However, when baleen whales eat plankton (including krill),
they are - like sperm whales and pilot whales feeding on squid -
essentially taking in prey which has the same salinity as that of sea
water. as a result, they must pass large quantities of urine to shed
the salt.

One thing cetaceans have going for them is that they don't sweat, so
there is no loss of water through the skin. Furthermore, the high
metabolic rate of cetaceans leads to oxidation of large quantities of
food, a process which produces a great deal of water as a byproduct.

The kidneys are central to all this, however. Cetaceans all have
exceptionally large kidneys relative to body weight (and allometric
considerations) when compared to most terrestrial mammals (although
those living in a desert environment share a number of characteristics
with cetaceans). The number of lobes (renculi) in the cetacean kidney
is also very large, and each of these lobes is essentially a kidney in

Not surprisingly, the kidneys of the river dolphins (which live in fresh
water and eat fresh water prey) are smaller and less complex relative to
those of salt water cetaceans.

Phil Clapham

Ron McGinley wrote:
> What biological adaptations do salt water creatures have that enable
> them to live in the high saline environment of the ocean?


Phillip J. Clapham, Ph.D. Large Whale Biology Program Northeast Fisheries Science Center 166 Water Street Woods Hole, MA 02543

tel (508) 495-2316 fax (508) 495-2258 Internet:

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