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:
One stopwatch
Electrode

Oscilliscope
Additional electrode for electrical stimulation

preamplifier
Amplifier

55 gallon tank
Live weakly electric fish

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.