View Full Version : Re: Rat Swimming

07-31-1996, 01:53 AM
Dear Dr. Slater,

You need to look at experimental biology papers, this sort
of thing has been done for almost 50 years for fish and swimming
animals. Try J. Gray papers (a series of 6) in J. Experimental
Biology (around 1910-1920). Generally, it is easier to move the water
past the animal rather than let the animal swim through still water,
unless you have a large tank. As you rightly mention, wall and floor
effects are a problem with small swimmers in confined tanks. Paul
Webb (1975) Bull. Can. Fish. Res. Bd. outlines all the
considerations required before carrying out search
experiments. It is a famous text - ask about it in the
Zoology department, if there are any fish biologists there.
Hydrodynamic texts include the very unique Fluid Dynamic Drag
(1965) by Hoerner, S. (published by himself) - really an engineering
text dealing with rigid bodies, but it has some equations and many
diagrams which you might find useful - try the engineering

I have also answered some of your questions below:

1) Should the containment system be made of plexiglass or glass? Whatever
material selected has to stand up to the stresses of the cage washer but
I also wonder whether one material will introduce a greater amount of
distortion than the other. Are there other considerations in making this

- Glass or perspex does not matter it seems. Perspex is lighter and
tougher (i.e. more resistant to crack propagation), but is less hard,
and more easily scratched. We made a huge 10 m diameter doughnut
respirometer filled with water (8 tonnes!) sitting on the bottom of a
huge concrete tank out of perspex without any problems - J. exp.
Biol. 1993, Lucas et. al. (December issue I think), has a diagram of
this and some methodology. This work formed part of my PhD thesis
(1993). The wall and floor effects are important if you want to
calculate the forces, but if you just want to see if it swims....

2) Can the methodologies used to analyze human swimming be applied directly
or does the more confined nature of a rat in a box relative to a human
in a pool alter the equation? More specifically, how can I best deal
with the distortions I expect due to the confinement system and water?

- Ok, you need a tank which is large enough such that the walls and
floor are sufficiently distant as to be regarded as 'at infinity',
the hydrodynamics texts say. Also, surface splashing effects are
difficult to calculate. They had to the forces and energy required to
move through water (which is why Olympic swimmers can only take a
certain number of strokes underwater before surfacing). Estimates
have been between 5-10 times as much energy to swim at the surface at
a given speed than if completely submerged underwater. Again the
submergence should be such that the surface can be regarded to be a
infinite distance away from the animal. Ideally you need to have the
rat suspended in mid-water in a completely still water tank with
walls several feet away in all directions and this same distance
beneath the surface of the water for the hydrodynamic analysis to be
Again many zoologists around the world send papers on animal
terrestrial and aquatic locomotion to the Journal of Experimental
Biology - which is the most prestigous journal in this field.
Probably the best way is to look back at all the issues (contents on
the back of the back cover) and scan the titles. People send in
models for fish swimming (like I have used), lizards running across
water, cockroach locomotion, flying bats, flying insects etc. You
should be able to find a rat locomotion paper in there somewhere
fairly recently.

3) Can rats with paralyzed hindlimbs swim? Obviously, I could
take some of the pilot animals drop them in an aquarium but I
hate to stress the
animals in that way if some of you already know the answer. Besides,
my past experiences with stressed rats resulted in blood loss (mine) and
a tetanus shot that hurt worse than the bites.

- not sure about this, probably best to try it at see. Try
blindfolding the rats somehow so they cannot see the situation, so
reducing their catecholamine levels. J. Gray (1913 - I think) in his
series on swimming animals in J. Exp. Biol. (mentioned above), found
that dogfish could swim using their spinal reflexes alone after the
spinal cord had been severed at the cervical level. May be rats have
a similar survival reflex - but being land mammals, I doubt it. Still
they are nature's survivors. In a recent Wildlife special (about 3
months ago now. David Attenborough (who btw, loathes rats), narrated
the BBC1 documentary, showing how rats living in sewers tended to
drown if the sewers flooded in a rainstorm. Perhaps they were not
adapted for water.

I am sure someone has already analysed this problem (a biologist
with a mathematical bent), you just need to find the name and
reference. As a last resort, phone Professor R. McNeil Alexander (or
write to him) at the Department of Applied Biology, University of
Leeds, Leeds, England, UK. He is the world authority on terrestrial
locomotion (though not swimming mechanics), and should be able to
give you directions. He is also a really nice guy.

Best wishes,

Julian W. Tang MA PhD MB BS.
University of Sheffield.

Thank you for your time and consideration of these questions. I will happily
post any responses.


William (Bill) Siler, Ph.D.
Saint Louis University