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Electric Fish
Jamming Avoidance Response
Purpose:
The purpose of this experiment is to record and analyze the Jamming
Avoidance
Response (JAR) of the weakly electric fish. The JAR occurs when two fish
emmitting
similar frequencies enter the same area and, to avoid subsequent confusion
of signals,
adjust their EOD frequencies, one fish up, the other one down. In
performing this
experiment, you will gain valuable experiance using electrical
equipment. You will also gain a greater understanding of the EOD
and its role in communication between weakly electric fish.
Materials:
Procedure:
- In a tank with only one fish, isolate and immobilize fish in
pantyhose
contraption.
- Measure and record period and amplitude of fish?s EOD. To
find period,
use a compass to determine horizontal distance in centimeters from two
peaks of EOD
on oscilloscope. To measure amplitude, measure vertical distance between
highest
and lowest peak.
- Convert period to frequency using the equation: frequency =
1/
period. This will give you the frequency in waves per millisecond.
- Measure period of stimulating electrode discharge in empty
tank as
described above. Adjust the frequency and amplitude knobs until the
signal on the
oscilloscope is slightly faster (less space between peaks) and sound is
slightly
higher than that of the EOD. Convert period to frequency following same
procedure
as above and record. Measure and record amplitude. Make sure you do this
in a
tank without a fish.
- Place stimulating electrode close to fish without touching
it. One
person starts the stopwatch. One person watches the oscilloscope and
listens and
tells stopwatch person when fish?s frequency changes. As soon as
frequency
changes, stop stopwatch and record the time it took to change.
- Measure and record period (convert to frequency) and amplitude
of
altered EOD.
- When stimulating electrode is removed, start stopwatch. Stop
stopwatch
when EOD shifts back to original frequency and amplitude. Record time.
- Measure and record the period (convert to frequency) and
amplitude of
fish EOD after stimulating electorode has been removed.
- Repeat steps 1-7 with a slightly lower frequency coming from
the
stimulating electrode.
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