🚀 go-pugleaf

I am on staff at a local science museum, and have been asked to modify an
exhibit there. I have a frustratingly simple question about this piece
that, so far, has not been answered to my satisfaction. (Actually, it's
sparked some rather interesting discussions on animal behavior and
instincutal vs. learned responses.) As there is no icthyologist authority
on staff, and my colleagues tend to disagree with one another, I thought
I'd pose the question here.
 
In this particular exhibit, visitors press a button which starts a current
flowing in a nearby aquarium. In this aquarium, tropical fish (namely,
tinfoil barbs) group up and swim into the current, as close to the source
of the current as possible. (Later, the motor resets and the visitor can
press the other button and get the current flowing in the opposite
direction; the fish swim towards that end.)
 
My question is: Why do they swim against the current?
 
Obviously, if they didn't, they would get swept "downstream" (or knocked
into the opposite end of the aquarium). However, is this behavior merely a
defense mechanism (so they won't get hurt), or does it have greater
significance?
 
Is it difficult for them to breathe when swimming with the current? What
are the physiological reasons for this behavior? Is this merely a reaction
to oncoming water, and a way to conserve energy? (One of my colleagues
offered this analogy: when you're at the ocean and a wave comes, it's
easiest to dive into the wave than to try to block it. Is this a fair
comparison?) Perhaps this behavior is utilized in their natural environment
(i.e., for catching food)?
 
Or is it a combination of all these things and not the wonderful, elegantly
simple explanation (tailored for a science exhibit) that I was hoping for?
 
Any input (though it may add to my confusion) would be much appreciated.

Jim
 

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