Ask A Scientist Zoology Archive

name         Phyllis P.
status       educator
age          40s

Question -   Fish have gills instead of lungs for breathing.  Correct?
Doesn't this mean that fish are able to get oxygen from the water that 
they swim in?  So this would mean that a fish could survive in a fish
bowl 
provided of course that the water is kept fresh.  Correct?  Is this true
for Betta fish?  I read that they have a breathing system called labyrinth 
which functions similar to human lungs.  The article I read said something 
about them "coming up for air."  This sounds strange to me.  Is it true?
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Phyllis,

Many fish can "gulp" air (if you like).  Betta sp. and all goldfish,
carps are known for this behavior.  It is a survival adaptation, and it
is found in many other species.

Water carries very little dissolve oxygen in comparison to the
atmosphere.  Gills are a much better apparatus for taking oxygen out of
water than lungs are for taking oxygen out of air.  Lungs can afford to
be less efficient due to the fact that oxygen is so plentiful in air.  

Gills work on an elaborate system of moving water over its intricate
blood vessel arrangement to draw out as much of the limited oxygen
supply out of the water.  Gills have one drawback, they must be kept
moist for their membranes are thin and susceptible to drying out, thus
destroying the tissues.

Ok, why did I tell you all of this!  Gills will work in taking oxygen
out of air, actually, better than lungs!  If a fish gulps air in
polluted or poor oxygenated water, the gills can do just fine, IF kept
moist.  

Many adaptations have evolved to support fish and gas exchange.  Yes,
the labyrinthiform organ found in some fish behind the gills can indeed
be used to store air for periods of time.  However, there are many other
arrangements in different species that do the same thing in different
ways.  Most fresh water boney fish have air sacs that they fill and
empty that serve as a means to move deeper or shallower in water without
effort, like a submarine. This organ also serves a breathing function in
many fish.

So the answer to your question is YES!

Steve Sample
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