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Drinking has long been established as an essential component in the homeostatic control of body fluid and ionic balance. In
 

Summary: Drinking has long been established as an essential component
in the homeostatic control of body fluid and ionic balance. In
terrestrial mammals, a 12% deficit in cellular fluid volume is
sufficient to induce a powerful drinking response, whereas
810% of extracellular fluid loss is required to induce
dipsogenesis (Fitzsimons, 1998). As a consequence, an increase
in plasma osmolality, or hyperosmoraemia, acts as a more acute
trigger for drinking in mammals than a reduction in extracellular
fluid volume or hypovolaemia (Fitzsimons, 1979). However, in
aquatic vertebrates such as teleost fish, hypovolaemia appears to
be the main drinking stimulus (Takei, 2000).
In the hypo-osmotic environment of fresh water, osmotic
gradients favour the passive entry of water across semi-
permeable membranes such as those of the gills in teleost fish,
negating a requirement to drink (Maetz, 1970). However, in
the hyperosmotic environment of sea water, water is constantly
lost and teleost fish drink to maintain ionic and water balance
(Oide and Utida, 1968), with excess ions being excreted at the
gills and/or kidney (Evans, 1993).
In contrast to marine teleosts, marine elasmobranchs

  

Source: Anderson, W. Gary - Department of Biological Sciences, University of Manitoba

 

Collections: Biology and Medicine