Friday, November 30, 2012

Fish Stories

In my book, I describe fish that make choices like we do, learn to follow gestures, enjoy roller coaster-like sensations, and handle delays to rewards (and more)., aquarium fish can learn to do things like swim through a hoop, and you can view cute videos on both of the animal training/enrichment websites in my "Links" page:  Karen Pryor's (also check out the blogs) and Mary Hunter's On youtube, you might want to take a look at "Phish’s Target Training" and "Limbo Perch clicker training."  Yup, perch can do the limbo.

What about fish in the wild?  One way that wild fish got to show off provided a great example of signal learning in a lab many years ago.  What actually happens in their natural habitat may involve much of the whole nature-nurture system. 
For generations, people knew that salmon fry hatched in freshwater, swam to the sea, grew large, and then returned to freshwater streams to spawn.  But which streams?  Early experiments in which the young salmon were distinctively marked or tagged showed that they returned to the same streams where they started.  Yet there they were in adulthood, hundreds or even thousands of miles from their homes.  How could they find their way back?  Many suggestions were offered, but I don’t believe anyone guessed part of the answer:  When they get close, they smell their way to their birth stream.

Step back in time.  One 1950s research project rewarded salmon for learning to tell the difference between 14 kinds of aquatic plants by smell.  They did just fine.  Given this clue, follow-ups confirmed that salmon could smell the difference between water from different streams (and had preferences).  Why do they wait for years to return?  As always, "it's a system," and there clearly are unlearned, "instinctive"-type components in this case--the sort of interaction described in my book.

Now that so many salmon runs have been driven to extinction or near-extinction, it’s especially important to try to understand how salmon homing works.  In a recent research article in Transactions of the American Fisheries Society, Andrew Dittman and his colleagues noted that chinook salmon reared in hatcheries sometimes homed as expected when the time came, but all too frequently returned to spawn miles away from where they had carefully been released--and that's a problem for restoration efforts.  Does this modifiability reflect any learning from consequences?  We don’t know for sure, but as Dittman mentioned, the full story probably includes many elements of the nature-nurture system.  That's just what we’ve come to expect.  

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