MadSci Network: Zoology
Query:

Re: Do salmon die after spawning because of osmosis?

Date: Tue Oct 28 08:18:27 2003
Posted By: Sue Kelly, Faculty, Environmental Science & Biology, Piedmont College
Area of science: Zoology
ID: 1065398636.Zo
Message:

Well, this is a good question.  I've never heard or read that salmon die 
because of problems with osmosis.  

It is a great hypothesis, though, since the adults come from saltwater & 
spawn in freshwater.  But, the adults of some species of salmon actually 
spend a year or more in the freshwater before they spawn, so they must 
have the ability to alter their physiology to cope with the change from 
saltwater to freshwater.  This isn't exactly a surprise since the smolts 
(juveniles) make the physiological changes necessary to move from 
freshwater to saltwater and we know the adults must survive long enough in 
freshwater to make the often long trek up the river.

Pacific salmon are the salmon best known for swimming upstream, spawning, 
and dying.  They don't eat on their journey upstream, they expend a lot of 
energy getting to their spawning grounds & making the nest, and they 
simply die from exhaustion based on what we understand.

It sounds as if you have probably spent a significant amount of time 
searching the Web already, but here are some websites that may be new to 
you:
 http://biology.usgs.gov/wf
rc/salmoq&a.htm
 http://www.mbstp.org/salmon.html
 http://www.cf.adfg.state.ak.us/geninfo/research/genetics/kids/salsto
ry.htm
 http://it.stlawu.edu/~fwbio/
salmon.html

Hope this helps!

Sue
MADScientist

**************

Moderator's addendum:

The physiological changes that occur when Pacific salmon enter freshwater streams to spawn can 
be attributed to both starvation and overproduction of steroid hormones.  The high levels of 
steroids result in degeneration of internal organs (heart, liver, kidney, spleen, thymus) and reduced 
immune function, rendering the animals vulnerable to bacterial, viral, and fungal infections.

Reference:  Helfman, G.S.; Collette, B.B.; and Facey, D.E.  2000.  The Diversity of Fishes.  Blackwell 
Science, Inc.




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