Sensorimotor integration: The Jamming avoidance response of weakly electric fish, Eigenmannia. www.jyi.org/articleimages/905/originals/img0.jpg. Glass knifefish. Eigenmannia virescens. What is an electric fish?.
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The Jamming avoidance response of weakly electric fish, Eigenmannia
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?
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.
(Based on the voltage of EOD)
Weakly electric fish (several hundred millivolts)
Strongly electric fish (several hundred volts)
(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)
Composed of electrocytes
Myogenic: Derived from various types of muscles
Neurogenic: Derived from modified spinal motor axons
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.
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
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.
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.
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
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
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.
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
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
added and presented.
Electrical fields had different
Frequency, but identical geometry
NO VARIATION IN MIXINGRATIO OVER BODY SURFACE----NO JAR
Under natural situation
electrical fields vary both in
frequency and geometry
VARIATION IN MIXING RATIO-----JAR
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