MadSci Network: Zoology |
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.
Try the links in the MadSci Library for more information on Zoology.