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Sensorimotor integration: The Jamming avoidance response of weakly electric fish, Eigenmannia. Glass knifefish. Eigenmannia virescens. What is an electric fish?.

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Sensorimotor integration:

The Jamming avoidance response of weakly electric fish, Eigenmannia

Glass knifefish


Eigenmannia virescens

What is an electric fish?

Electric fishes: have the ability to generate an electric field---Electrogenic.

Knifefish, Torpedo, Elephantnose

Electrogenic are also electroreceptive.

What is not an electric fish?

Apteronotus albifrons

Fishes that are able to detect electric field but are not able to generate an electric field. Electroreceptive : Ability to detect electric field.

Sharks, Skates, Rays and Catfish


Electric fish species can be found both in the sea and in freshwater rivers of South America and Africa.


Electric fishes:

(Based on the voltage of EOD)

Weakly electric fish (several hundred millivolts)

Strongly electric fish (several hundred volts)


Electric fishes:

(Based on the discharge pattern)

Pulse type: Brief electrical pulses followed by variable intervals of silence.

Elephant nose (Gnathonemus petersii)

Wave type: Sinusoidal with duration of electric pulses comparable to duration of interpulse intervals.

Knifefish (Eigenmannia sp)


Electric Organs

Composed of electrocytes

Myogenic: Derived from various types of muscles

Neurogenic: Derived from modified spinal motor axons

(oder Gymnotiformes)

Number of electric organs may be one or more than one.

Electrocytes are arranged in series. Simultaneous firing of electrocytes results in the electric organ discharges (EODs) which are emitted in the surrounding water.


Electric organ is innervated by electromotoneurons

Innervation site has distinct evagination---stalk

The regularity of the electric organ discharge is determined by an endogenous oscillator in medulla oblongata called the pacemaker nucleus (PN).






Specific sensory cell that mediates the perception of electric signal

  • Senses
  • own EOD
  • EOD of other fishes
  • Abiotic sources

Mark Nelson

Electroreceptors are abundant in the head region




T type (Phase)

P type (Amplitude)


Electrolocationis the ability of electric fish to detect and localize objects around them. It allows electric fish to hunt and navigate in the absence of visual cues at night or in turbid water.

Conducting object

Electric Current

An object with higher or lower conduc-

tivity than the surrounding water causes

distortion of the electric field lines. This

causes the area of the skin nearest to

the object to have different voltage than

the rest of the body, which the fish can

monitor by its electroreceptors. Thus, it

locates the object.

Electric organ

Electric organ


Jamming Avoidance Response (JAR)

Eigenmannia virescens

The most intensively studied behavior of electric

fish is the JAR of high frequency wave type species.

What is JAR ?

The fish’s ability to electrolocate is affected in the presence of another fish with similar EOD frequency. The two electric fields interfere with each other resulting in phase and amplitude modulation of each of the two electric signals. This impairs the fish’s ability to electrolocate.

In order to avoid such detrimental interference of the two electric fields the fish shifts its own frequency away from that of its neighbor.

This behavior is called JAR


JAR leads to two distinct behavioral patterns

If the neighbor’s EOD frequency is higher than the the fish’s own frequency

then the fish lowers its EOD frequency.

If the neighbor’s EOD frequency is lower than the the fish’s own frequency

then the fish raises its EOD frequency

DF(frequency difference) = Neighbor(f) – Own(f)

Lowers its frequency if DF=(+)ve

Raises its frequency if DF=(-)ve

BEFORE JARfA=300Hz, fB=304Hz

AFTER JARfA=292Hz, fB=312Hz

Frequency shift evoked when DF < 20Hz


Silencing of electric

organ with curare.

EOD replaced by electric sine wave of similar amplitude and frequency

Mimic of neighbor’s electric field

Result: Correct jamming avoidance behavior

Lowers its pacemaker frequency if DF=(+)ve

Raises its pacemaker frequency if DF=(-)ve

Do not tell much about the behavioral mechanism involved in

determining the sign of DF.


Frequency of the EOD mimic was decreased to a frequency

50 Hz below the frequency of the pacemaker nucleus

When confronted with neighbor’s EOD mimic it responded as if this 50 Hz lower frequency was its own frequency.

Pacemaker (f) =100 Hz

EOD mimic (f)= 50 Hz

Neighbor’s EOD mimic (f)=54 Hz

Uses the electrical field frequency rather than internal frequency

of the pacemaker nucleus----- NO INTERNAL REFERENCE


Fish placed in two compartment chamber

Pectoral region sealed

No EOD could be detected by head region

Jamming stimulus presented to the head



JAR elicited when

EOD leaked into head chamber

Jamming signal entered the tail chamber

Fish needs a mixture of its own signal

and neighbor’s signal to execute JAR


Mimics of two EODs were

added and presented.

Electrical fields had different

Frequency, but identical geometry



Under natural situation

electrical fields vary both in

frequency and geometry



The amplitude and the phase of the mixed electric field signal

is different from the amplitudes and the phases of the individual


Moreover, the amplitude and phase of the mixed signal are

modulated over the body surface of the electric fish.

By sensing this modulation of the amplitude and phase, the fish can

determine if the other signal has a lower or higher frequency.

Important requirements for JAR:

1. Absolute value of the difference in frequency less than 20 Hz

2. Mixing of signals

3. Variation in mixing ratio

4. Modulation of phase and amplitude of the mixed signal