swim bladders

James Mahaffy mahaffy at dordt.edu
Thu Oct 12 02:37:41 EST 1995

BAKERG at par18.aph.gov.au wrote:
: Can someone tell me exactly how fish swim bladders work?
: Do they alter the volume of the fish?
: Or do they change the weight?

: Any help appreciated. References would be useful.

: Greg Baker

John V. gave you a reference (almost any good book on fish [icthology])
should explain it or even a basic Zoo text.  I am not an fish person,
but let me try and give a simple explanation. Fish are made of soft
tissue which becomes compressed and hence denser as they descend.  That
means of course that they occupy less volume and will no longer be
neutrally bouyant.  By pumping gas into the swim bladder (using a very
fascinating system of blood vessels) they increase their volume with a
gas that weighs less than muscle tissue.  The weight of the bone and
muscle had never changed it had just been compressed into less volume, but
now the added volume of the swim bladder (with gas that is lighter than
tissue) results in neutrally bouyant fish.  However if you pull the fish
up quickly form the bottom the gas (which was under pressure) will expand
faster than the fish can remove the gas (which it must do as it rises).

	Hope that helps. It is too late at night and I should get back to a

James F. Mahaffy                   e-mail: mahaffy at dordt.edu
Biology Department                 phone: 712 722-6279
Dordt College                      FAX 712 722-1198
Sioux Center, Iowa 51250

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